Traditional Leaded Light Construction

It’s not often that I construct a leaded light but having done so recently I thought I should share some notes with you. They may help you as a newcomer or give you some new ideas if it’s an activity you’re already familiar with.

I really cannot claim to be an expert so you might have different opinions and ideas and might even think I’m doing it all wrong. Use your own judgement and decide for yourself. Sharing the information is what’s important from my perspective.

Rather that write this blog as a tutorial, for which there are several to be found online and in books, I will break down my notes into short sections that broadly follow the construction steps but I will not concern myself with step-by-step instructions. Sorry if you find this results in a blog that is a little incoherent at times.

Two Schools

There are two schools of thought about what to do once a cartoon has been produced. The difference lies in the method by which a cartoon is translated into a set of glass pieces ready to assemble.

Incidentally, I use the word “cartoon” for a drawing of an intended design. You might be more familiar with “pattern”. I think there’s a subtle difference that makes “cartoon” more appropriate but we can beg to differ on this little matter.

The first school of thought is that you must make a copy of your cartoon and use scissors on the copy to make little templates that represent each of the pieces of glass. I find this time consuming and fiddly so only use this method when I am using opalescent glass or dark colours that I cannot see though.

The second school of thought is to use the cartoon to directly score the glass directly over the original cartoon. This is a quicker method, lazy some might say, because it requires no copy to be made and there is no scissor work. This is what I tend to do if I am using glass that I can see through. I also prefer this method because and there are no fiddly bits of paper getting in the way of glass cutter wheel and no little pieces of paper to lose. One might suppose that parallax error might make this method slightly less accurate because of the distance between the cutting wheel and the cartoon lines but for leaded light work this does not tend to be a problem.

As already mentioned in passing, I still sometimes have to use the first method when working with a dark cathedral or opalescent glass. In this situation I mark-out a copy of the pattern for individual glass pieces using tracing paper, cut-out the tracing paper and use this as the template. I then use a waterproof marker pen, or a white wax pencil, around the edge of the template to mark-out the perimeter onto the glass. I don’t stick the paper onto the glass and attempt to score around it as I find the outcome is worse score lines.

Whichever method you use, it can be a good idea to number the pieces of glass to match the number you’ve added to the cartoon (and maybe template pieces) so that you don’t forget where they go and indeed which way up the pieces of glass should be used. This is particularly important when the design is complicated and has many pieces of glass that are similar but not exactly the same.

DSCF3325 CartoonSomething extra that I do with leaded light cartoons is to pencil-in lines that represent the boundaries between the glass and leads. Whilst doing this I also consider how the pieces of leading will affect visual appeal, construction strength, how it will be assembled and so forth. So, in addition to marking-out where there will be leads I also mark how those leads should be cut and jointed as a reminder for later. Look at the picture for a better understanding of what I mean.

The thick black lines on the cartoon will be explained in the next section.

Can you see I stopped bothering to mark out the cames and joints in the lower part of the panel because it was the “easy and obvious” part? I find that marking-out the cames and joints is more important for the complicated or intricate areas than elsewhere so I sometimes allow myself to be lazy in the less critical parts of the design.

If you leave these assembly and jointing considerations until the assembly phase of the construction and try to do it “on the fly”, your mind and your eyes will tend focus on the immediate task at hand – which is to say the current piece of glass and lead came. This means you will tend to neglect the “bigger picture” and often forget any thoughts you had about what to cut, where to joint and so forth.

Another dividend is then repaid when assembling the panel because you instantly see whether or not each piece of the lead work is being placed exactly in the correct position and is the expected shape. This in turn means construction problems are caught early and can be addressed immediately. You don’t have to wait until the panel has been fully assembled to realise that lots of subtle little errors have produced a wonky distorted panel that’s not quite the size it was meant to be.

Cutting the pieces of glass to the “right size” is important and the “right size” depends on the construction method and materials being used.

If you simply score along the cartoon pattern lines your will end up with glass pieces that are too large because no allowance has been made for the thickness of the lead between pieces of glass in a leaded light. A different allowance must also be made for the a double-thickness of copper foil (and a little solder) when using the copper-foiled method. So, the “right size” is a little smaller than the size on your nicely drawn cartoon drawing.

Commercially available pattern shears are available that will automatically cut on each side of the cartoon’s lines to help you with this task but I do not use them. One kind of shears is for copper-foiled work and the other is for leaded lights. The only difference between them is the amount of size-trimming that they perform. But there is a simpler method that is not only cheaper but is, at least in my opinion, more effective…

Look back at the previous picture and notice the thick black lines. Then read on…

Mark out all the glass boundary lines in your cartoon design with a felt tipped marker pen that produces lines about 2mm thick if it is going to be a leaded light. If you intend to use the copper-foiling method then a finer marker pen that produces lines no more than 1mm wide is appropriate.

You will then score along the edges of these marker pen lines, not the middles of them.

Thus, the thick marker-pen lines represent the channels inside your lead cames. Because 2mm is slightly more than the thickness of lead in the channel we can be sure the pieces of glass will not only fit but should rattle slightly.

The reason we should aim for slightly under-sizing the glass pieces is to ensure that the panel as a whole can be constructed exactly as the cartoon design intended, which is to say the final product will not contain distortions and can be made to exactly the correct dimensions. Although there will be some rattling of glass pieces around the constructed panel it will be entirely resolved by the waterproofing and strengthening stage of construction. But, there is a difference between being “a little too small” and “too small” and it depends on the width of the lead cames you are using. Wide leaves (flanges) of chunky cames means you’re allowed more latitude. Narrower cames demand more careful cutting!

And by the way, if you have the habit of using waterproof marker pens to mark-out the glass cutting lines then a smear of something like petroleum jelly (eg Vaseline) will help to stop the lines washing off when subsequently grinding. An alternative is wax pencils. A lazy third alternative is to place a sheet of clear acetate over the cartoon to protect it from water, then repetitively grind and check the piece of glass against the cartoon.

Obtaining and Storing Lead Cames

Lead cames are produced in straight lengths and that’s how you should try to obtain them. Avoid buying lead cames that have been coiled-up because it requires more effort to straighten them and increases the chances of physical damage. If this means you need to visit a stained glass supplies shop one per year rather than have it posted to you in coils then do so.

Once bought, give some thought to transporting and storing your lead cames straight and flat. Some possibilities are a long sturdy cardboard postal tube, a piece of plastic drainpipe or even a piece of plastic guttering. You glass supplier receives the lead cames in crates – maybe they are kindly folk and have one spare that you can have.

If you live in a damp environment, or your work area gets damp, try not to buy more lead came than you need as it will deteriorate through oxidation and become harder to solder. If you live and work in a nice dry environment then this is less of a problem so buying in greater bulk is more viable.

I have in the past been “donated” really old lead cames that had lain unused for many years. They had almost turned to black and were an absolute swine to solder and it was (in practical terms) impossible to “brighten” the leads where I intended to solder. So, if someone approaches you with a fist full of twisty mangled ancient lead cames, politely decline the offer even if they are free!

I should perhaps briefly describe some common forms of lead came, particularly for novice readers. What you choose comes down to artistic necessity, suitability and experience.

H-section cames are what you will mostly use so I will talk mostly about them. You will notice they have 5mm wide channels into which the glass pieces fit. The overhanging leaves (flanges) will keep the glass in place even before you’re waterproofed and strengthened your masterpiece.

But why not a 3mm channel for the glass we tend to use? The answer is easy. Think about the effect of surface patterns and the thickness variation of hand-blow glass. The extra 2mm is needed to accommodate such situations!

Another aspect of H-section cames is that the leaves “overhang” the glass by differing amounts. In this regard it is like choosing between thin or fat copper foil – part of the choice relates to the visual effect but there are also underlying practical consequences. A consequence of choosing H-section cames with wide leaves is that there is more latitude for error in the glass cutting and a stronger layout at the expense of a “chunky” appearance to the finished piece. Finer cames demand more accurate glass cutting just as using skinny copper foil only looks good if you cut the glass accurately.

H-section cames are available with “leaves” that are may have flat or curved outer surfaces, or both. In practise it doesn’t matter whether the leaves are flat or curved, and you will not really notice the difference except in one situation – accidentally mix them up in the same piece and it looks shabby with both flat and curved surfaces on the same side. I’ve accidentally done this in the past so trust me!

There is no reason why you cannot mix-and-match different types of H-section came in the same piece. For example, if your design contains a nice traditional stylised flower (not unusual!) you might choose a “fatter” came below to represent a stem for that flower.

U-section came and C-section came need special attention because their names are often confused. U-section came isn’t just C-section came turned on its side! They have different cross-sections but more to the point, they have very different purposes.

C-section came might have curved or squared-off outer profiles when viewed in cross-section and tend to be used to form a framing edge for a panel or inside a wooden frame (eg a cabinet door). Consequently they are often used for a standalone piece such as a suncatcher and sometimes have a narrow channel that is around 3mm rather than 5mm so be careful before your buy such cames. Incidentally, I hate the term “suncatcher” because they don’t catch the sun and they’re not necessarily hung in a window and it explains why I tend to use the word “panel” instead. But again we can agree to differ!

C Section Came UseU-section came is interesting. When you find some to look at, notice the heavy-duty curved outer profile in cross-section. The reason for such a sturdy curved profile is because U-section intended to be used as the upper edge of a large panel section that will have another panel section resting on top. To understand what I mean, think of a massive stained glass window in a church which has, by necessity been constructed in sections. Now look at my rubbish little diagram to understand how the H-came (in red) and C-came below (in blue) are being used. Over time the H-section presses down under the weight of the upper panel and the H-section’s leaves will splay and form a nice neat seal over the C-section curve below. Rainwater will remain outside and not be drawn into the panel. A simple solution to making a massive glass window panels waterproof wherever they meet. Our ancestors were not so primitive as we sometimes assume!

And finally, remember there are other forms of lead came for special situations. Some cames are for forming a right-angle joint. There are others designed to be the perimeter of a piece that makes it easier to mount into a frame. Visit your stained glass shop or look at a web site and ask what they are intended for. Nice people like to share their knowledge and experience.

Stretching Lead Came

Lead came needs to be stretched a little before use, not only to remove kinks but also to make the structural properties of the lead change. Somehow a stretched came seems to be a little stronger.

Stretching ought to be done only once per came, so to avoid confusion don’t stretch a came until you need it and store leftovers in a different place from un-stretched cames.

Two people holding each end of a length of lead came with pliers (or a similar tool) can perform the stretching. If there is nobody to help you then a lead vice will be needed and the vice must be screwed to a table top or clamped into a sturdy vice. Don’t attach the lead vice to your best table and don’t trap one end of the lead came into a door frame – these are both effective ways to damage woodwork!

How far to stretch the cames is a matter of judgement. What you are aiming for is the removal of kinks plus just a little more. Do not pull too hard or stretch too far as the lead will start to lose its strength and become softer. Worse still is if you pull too hard and the lead breaks (usually at the pliers) because you will find yourself flying backwards uncontrollably!

Although kinks can be removed from a lead came by stretching, nicks and most crush-damage can not. A problem with lead is that it is very soft and therefore very prone to damage especially on the leaves. At best you might be able to use a lead knife blade or an All Nova tool to “flatten out” some of the damaged areas but, of course, you will be cutting up the cames in various lengths so you can plan to cut pieces between the points of damage, or if you’re sneaky you can ensure damaged areas are soldered over at joints. Constructing a panel from damaged leads, visible for all to see, reflects badly on your commitment to excellence so don’t do it. Hiding little areas of damage under soldered joints is another matter entirely!

From all this you’ll understand why it’s not a good idea to buy coiled-up lead cames and why it’s sensible to transport and store them tidy and flat. I’ve previously suggested cardboard tubes, drainpipes and gutters as suitable storage containers.

If you don’t have space to store your cames in full-lengths then you might try cutting them in half but this will limit the maximum size of panel that you can make. Another reason to cut cames into half lengths is when you’re not a strong athletic person or you’re on your own – it’s easier to pull a shorter length of lead came single-handedly.

Use an All Nova Tool

The All Nova tool is inexpensive and replicates the functions of traditional tools such as the lathekin, fid, oyster tool and others besides for burnishing, flattening and spreading came. Unusually for “multi-function” tools, which tend to do many things badly, this one is well-designed and does all the tasks asked of it properly. I think it’s an essential tool for anyone who does copper-foiling or leaded light work. Not really useful for fused glass work though.

I’ve never seen any “formal” instructions on what the various parts of an AllNova tool are designed for so here’s my take on what I’ve read and discovered for myself and I also attach a picture that also includes a few horseshoe nails and a few scraps of lead came (the purpose for which will become apparent later).

DSCF3326 AllNova ToolThe outside curve of the flat face at the flat end of the AllNova tool can be used for burnishing copper foiled work or to completely close the lead came channel gap around the peripheral edge of a leaded light.

The very end of the flat end of the All Nova tool can pushed into the channel of a lead came and gentle “pulled along” the channel to open-out a kink in the leaves of a lead came, or the flat face can be used on the outside of the lead came to close-up a kink in the leaves of a lead came. Although this flat end of the tool is useful for dealing with kinks and opening-up the channels, see below for how the heel at the “pointy end” can also be used to widen the channel down a full-length of a lead came in one simple action.

Another use for the end of the flat side of the tool, when inserted into the heart of a lead came channel, is to help push and shape the lead came around the profile of an adjacent piece of glass. This avoids the kinds of damage that your hands or some other tool might do when pushing against the structurally weak leaves of the cames.

And yet another use for the flat end is to gently open up the “crushing damage” that can and often does occur when cutting a lead came. Insert the flat end into the channel just behind the damage and pull through to the end of the came. The little crushed area at the end will be pushed back into shape. I sometimes also use of the flat-side of a lead knife to “finish off” the damage repair.

An All Nova tool can be used to widen the channel of a lead came if glass is too thick to be inserted into the channel easily, or if the channel is slightly closed. The heel area at the “pointy end” is a splaying tool. Hold the came end that’s nearest to you and put the ‘heel’ of the AllNova tool into the lead came channel nearest to you. Then gently push down the heel into the channel and push away from you. The amount of pressure downwards into the channel will affect how much you splay the leaves of the came so take care. Ideally, practise first on a pieces of scrap came to get the technique right. You will see the channel widen by an amount determined by the downward pressure being applied. If the channel is still not wide enough for your glass then you can try to pull back with the ‘toe’ of the All Nova Tool (remembering to now hold the came at the far end!). To be honest, I’ve never needed to use the toe-end of the tool as the heel seems to do enough of a widening job for my purposes.

A traditional oyster tool (long thin U-shaped blade with a handle) is another possibility for widening the channel of a lead came. There’s not much point in owning one if you already have an AllNova tool.

If you’ve used the heel to widen a came and it’s now too wide then the flat end of the AllNova tool can be used to reverse the over-enthusiasm. Press the flat side down and slide gently along the came to close-up the gap. A sort of gentle burnishing action you might say.

The pointed end can be used as a “picking tool”, for which the most obvious task is to remove excess cement after waterproofing a leaded light. Despite this suggestion, I tend to use matchsticks because they can be then thrown away. The pointed end could also be used for back-scratching and nose-picking. Well, that’s what I tell kids. Some believe me.

And finally, what’s the little hole for? To be honest I have no idea.

Preparing for Construction

Place your paper cartoon design onto a wooden base and firmly fix a batten along of the main (longest) edge of the design so that the design cannot move and you have an accurate straight edge to work from. Of course, this assumes you have at least one straight edge in the cartoon design.

Ideally I would add another batten at 90 degrees (or whatever angle is required) to form the second edge of the panel to ensure at least two side can be constructed with absolute accuracy. This also gives you a firm and well-defined corner out of which you assemble the panel. Get the angle wrong and the resulting panel will also be wrong!

I tend to leave a little gap between these two battens so that a lead came can “poke out” of the corner if necessary.

Masking tape is not very reliable to hold a cartoon design firmly, nor will it ensure that two sides of the design are accurately placed, but it is better than nothing.

Cutting Lead Came

There are different kinds of commercially available lead knife that are commonly used. The traditional ‘Don Carlos’ lead knife seems to be more expensive and in my experience works no better than a more modern lead knife.

Modern lead knives have a curved blade on one end (with a pointed end on one side) and metal cap at the other end of the handle. The metal cap is intended to be used as a hammer and is useful for driving horseshoe/glazing nails into the base board. It is a boon for lazy people because it means you don’t have to repeatedly swap between a lead knife and a hammer. Take care not to cut or stab yourself with the lead knife blade when hammering the horseshoe/glazing nails – enthusiastic hammering is a bad idea with a blade not far from your face!

An inexpensive alternative to the “proper” lead knives are putty knife or a cut-down wallpaper scraper which has been sharpened on a grinding stone (of the kind you would sharpen a chisel for example). Be sure the blade is strong and does not flex.

Later I have included a picture containing an improvised and a modern lead knife.

Just as the secret of a good steak is a sharp knife, so it is true for cutting leads. A blunt lead knife is harder to use than a sharp blade so sharpen the blade regularly. I use my kitchen knife sharpener for this purpose and it seems to work well enough.

There is something of an art to the act of cutting a lead. To begin with, place your H-section lead with leaves top and bottom and the channels to the side. Then, with the lead knife correctly placed above, use a gentle side-to-side rocking motion whilst pressing downwards. The wiggly rocking motion helps to work through the considerable amount of lead in the top leaves of the came. When you’re about to get through the top leaves, reduce your downward pressure because relatively little is then needed to push down through the channel part. And finally, increase the downward pressure to push through the lower leave of the came. If you can keep your knife vertical (except for the initial “wobbling” action) throughout this process you will get a nice exact 90 degree vertical cut. A nice vertical cut ensures the lead work is equally precise on both sides.

Practise makes perfect but sometimes some trimming may be needed to get the piece of lead to fit exactly in the panel. Hold the lead came in the same way and pare away at the end of the came until the exact length and angle is achieved. If necessary, flip it over and repeat from the other side. Wipe away the little pieces of scrap because they can damage a came if you subsequently try to “work” on top of one of them.

Once cut and trimmed to size there may be some crushing damage to the ends of the leaves. In addition to using the flat end of an AllNova tool to “pull though” the end of the channel I also use the pointed end of the lead knife to deal with any residual damage to the corners of the came. Crushing damage becomes an unavoidable problem when cutting the cames at shallow joint angles.

Remember that it is easier to cut the stretched came into smaller pieces to work with than a full length but it will mean a little more waste. Shorter lengths of came are also less likely to get twisted or damaged when they accidentally knock into other things nearby.

Use of a mitred or butted joint corners are equally acceptable. The choice depends on circumstances and generally butted joints are quicker and easier. Remember that the joint will be soldered so how you form the joint will not be visible. All that remains visible is the quality of your soldering!


Glass cutting errors are not so critical for leaded lights when compared with copper foiling.  Actually we should be aiming for just a hint of “rattle” in an assembled leaded light because it tells you there are no “pressure points” that might cause stress fractures later.

Ideally you should strive for a situation in which you rarely need to use a glass grinder to finish off pieces of glass for leaded lights. Pause for a moment to think about the glass workers of times past when electric glass grinders were not available. Getting it right first time was important because all you had was grozing tool with which to “nibble” the glass and a scythe stone. So, let the “leaves” (flanges) of the lead came be your friend as they hide a multitude of sins, such as slightly mis-shaped pieces.

Assemble from the longest side of your piece first. It is usual to start the assembly in a corner that will at the base, working piece by piece away from the corner and up the side and across. Pieces of came will need to be cut enclose each successive piece of glass that is to be added.

Although it’s a rather vacuous statement, remember to pause from time to time as you assemble the piece to review progress and plan what needs to be done next. For example, sometimes you may find that you need to build a whole “sub-assembly” and add it as a whole rather than add pieces one part at a time. Remember that you are aiming to make the pieces fit accurately over the cartoon design as well as constructing a strong panel that will look good when soldered. This is not a trivial matter so that’s why I try to plan and record my cutting and jointing intentions directly onto the cartoon in the design stage.

To a significant degree your cartoon design ought to address many of the visual appeal and strength issues but there remains the matter of how you cut and connect those pieces of lead came. For example, running single continuous lengths along the outside of each edge of the whole piece is good for the strength of the panel. But what about a circle within the design – are you going to have a single piece of lead coiled all the way around? Where will you “make the join”? Try to think before cutting and fitting the leads. Better still, do it in the design stage!

To stop the assembly from slipping and falling apart you will find it useful to strategically hammer horseshoe/glazing nails around the edge of the part-constructed panel wherever they are needed to stabilise the panel. A dozen of these horseshoe nails is adequate for a modest sized panel.

Before you start hammering those nails into your baseboard and against the leads I remind you that horseshoe nails are made from harder metal than lead and can therefore damage the leads. I therefore recommend you place a piece of scrap came between the cames of your panel and the horseshoe nails as a softer protective spacer.

DSCF3281 LeadedAt this point I think I need to relieve your boredom with a picture. So, to illustrate what I have been talking about, look at the picture of the assembled panel. Notice how the circular area containing the rosebud has been pre-assembled before insertion. Notice also the little mistake on the right-hand leaf where I’ve inserted a little fillet of lead to “fill the gap”. I’ll talk more about this “bodging” when I chatter about soldering. Notice also the use of horseshoe nails with little scraps of lead to hold the assembly firmly in place. And finally, you might want to compare how I cut the leads with how I planned to do it against the cartooned design.

The outer perimeter of the panel does not need to be cut to exactly the right size to begin with but will need trimming when you have finished. This is why I mentioned that I often leave a little “gap” between the battens earlier on in my chatter.

But you may be wondering, especially as a novice, how to remove at least some of the guesswork from cutting the pieces of lead came accurately. Am I right?

Well, it depends on the situation as to how to proceed, but one extra useful hint is that a scrap of came can be used to “represent” what has not yet been fitted. It’s easier to show you than write it down but I’ll try…

Imagine you have a single piece of glass in your hand and that it’s a quarter of a circle. You want to cut the curved piece of lead but realise that the two straight sides of the quarter circle will also have leading. So, either the curved piece of lead needs to be slightly shorter than the length of the curved edge or the straight pieces need to be slightly shorter than the straight sides. Aaargh! This is partly why I think about the cutting plan at the design stage.

Let us assume the straight sides of the quarter circle will have full-length pieces of lead came and that the curve must fit in the remaining space. We therefore want the curved piece to be slightly shorter than the length of the curve of the glass piece. But how much shorter?

To remove guess work from cutting this curved came piece accurately,  first apply your piece of came to the curve and push it into shape along the curve. You could use the flat end of an AllNova tool to help you do this without damaging the lead came. Allow this length of came to overlap the ends of the curve at each end. We know we need to cut “something” off each end so need to figure out where exactly to cut the ends in order for them to both butt-up accurately onto cames running along the adjacent straight edges.

With the overlapping curved came still in place, lay short lengths of scrap came just next to the overlapping ends of the curves on each of the adjacent straight sides. These two scraps shows you where the real straight cames will fit. So, lightly mark the curved piece of came at each end with your lead knife with lines that extend the inside edges of the two scraps.

With the curved came marked, remove it, put it on a nice clean work surface, then cut through the came at the required angles at each end. The quarter circle of glass and the curved came are now ready to be added to the panel. If necessary hold them in place with a horseshoe nail and protective lead scrap.

DSCF3329 CuttingThe picture you now see is an illustration of what I’ve just been talking about and also includes of a lead knife made from a cheap wall scraper and a “proper” modern lead knife. If you click on the picture it will display in greater detail in another window.

Incidentally, I’ve deliberately used old lead cames for this picture so that you can see what happens after several years of storage in a relatively dry environment. Notice they are looking distinctly grey.

The upper-right area of the glass piece illustrates how a scrap piece of lead can be used (across the top) to gauge and mark where to cut the long curved piece of lead (on the right). The lower-left area of the glass piece shows the next step, where the lead has been cut and you should immediately notice that the curved lead does not reach the end of the curve. Notice also that when you follow the straight piece of lead on the left, downwards along the inner edge, it leads you neatly past the end of the curved piece. This illustrates what you’re trying to achieve with each pieces of lead came in the assembly.

But what happens when you later find that you have an assembled panel ready for soldering and discover that one of the leads was 1mm or maybe 2mm too short? Such accidents do happen but don’t despair. By all means investigate to understand how the problem happened, and learn from the mistake, but don’t dismantle the panel to re-make that piece of lead came because there’s a sneaky trick you can use and it’s another use for little pieces of scrap H-section came…

Although this trick may seem to relate to soldering, I’ve put it here because really it’s more about dealing with an assembly problem caused by mis-cut leads.

To fill in a rather-too-big gap easily and invisibly, first cut a suitable short length of the H-came that will nicely fit into the gap above and below. Then, use your lead knife to chop out one side of the H so that you end up with a T and an I piece (or two stubby T pieces if you prefer). These two pieces can now fill the gaps on each side of the panel.

When you are ready for soldering, insert the T-shaped portion to bridge the gap and solder as normal. The solder flows over the insertion and your trickery then is hidden behind the solder joint.

Later, when soldering the back of the panel, use the remaining I shaped piece but be careful you don’t lose it in the meantime. No, actually it doesn’t matter if you lose it as you can easily make another!

Defects larger than 2mm can also be dealt with in the same way, provided they are shorter than the size of the soldered joint to be produced. But, if you’ve got a gap larger than about 3mm you should start to wonder how you’ve managed to cut a piece of lead so badly wrong and not notice it before!

This trick is not needed for tiny sub-millimetre joint defects because solder will happily bridge small gaps.

If you refer back to the picture-before-last, you’ll remember I filled a little gap with a fillet of lead at the end of a rose bud leaf. On this occasion the fault was only on one side of the panel so I could simply bridge the gap on one side. Again, this becomes an invisible mend because it will soon be covered with solder.

Soldering Lead Came

If you are a novice with leaded light construction you will discover that soldering a leaded light is not the same as soldering copper-foiled work. For this reason I recommend you do lots of practise joints until you can confidently and reliably solder lead cames.

What I describe works for me but to be brutally honest I ought to practise my leaded light soldering more often because is “a bit dodgy” sometimes. Ask around and watch other people soldering and they will reveal subtly different techniques. With time you will find a technique that works reliably for you.

The key to successful soldering is preparation. With copper-foiled work your “safety flux” removes oxidised copper and this helps the solder flow and bond nicely. The situation with lead cames is subtly different because a different flux is used and oxidation must be removed before the flux and solder are applied.

Some people may tell you to use a fine-grade wire wool to remove lead oxides (ie “make it shiny”) in preparation for soldering. I have tried this method and although it works I have two objections to it. One is that it produces a lot of dust from the wire wool breaking down into fine iron particles. The second is that the rubbing process produces a lot of lead dust, some of which will become airborne whilst rubbing and also when cleaning-up afterwards. Lead is nasty when it gets into your body so, for your own health, don’t make lead dust when there is an equally effective alternative method that doesn’t!

The alternative to using wire wool is to lightly roughen the area around an intended solder joint with the point of a lead knife or a horseshoe or glazing nail or, in truth, anything else that’s sharp, pointy and can be used to scrape the surface of a lead came. You only need to get the surface shiny around the exact area where you will be soldering. This is simple, it’s effective and it’s not going to harm your health.

Now that you have some lead prepared and ready to solder, there’s an extra step I suggest, if you have the patience…

Take a moment to pack a small piece of cardboard or folded paper between the glass and lead came in the area where the joint is to be soldered. This preserves the gap, protects the glass and perhaps more importantly, it eliminates solder bead drops which may ultimately cause a stress fracture in the distant future.

Next is the application of the soldering flux. For leaded lights the flux is tallow and the form commonly used looks like a candle minus a wick. The tallow should be rubbed around the surface of the area to be soldered.

The method of soldering is also different from copper-foiled work. First feed a little solder onto your soldering iron so that it holds a molten bead.

If you’ve read my chatter about choosing the right solder then you know you ought to be using a 40:60 solder rather than a 60:40 solder and should understand why. But I digress…

The aim is now to transfer the solder bead from the soldering iron to the joint without melting the lead around the joint. Much practise is needed to achieve consistently good results and the most important thing to understand is that a confident and quick technique is the key to success.

Slowly bring down the soldering iron tip (with the solder bead), but try to stop when the iron’s tip is a millimetre or so above the lead came. At this point the solder will “find” the lead and begin to spread out by itself. Oh for the joy of surface tension!

You can then deftly move the soldering iron around (still trying to hover) to help the solder flow around to where you want it do go. The aim is not to touch the underlying lead with the soldering iron because you don’t want to directly transfer heat from the soldering iron into the leads and cause them to heat up and melt more quickly. I suppose this technique could be likened to rolling a blob of sticky glue around – the objective is rolling, not squashing.

The reason you need to act quickly and deftly is that the lead cames and the solder melt at similar temperatures and it does not take long for the heat in the solder to conduct into the lead, heating it up to melting point. This also explains why we don’t want the leads being heated up more quickly by being in direct contact with the soldering iron. So, speed and accuracy is important. Starting the process with cold lead is also important.

In my experience “fiddling around” trying to “fix” a bad joint rarely achieved more than melting the underlying lead and make a crisis out of a disaster. If you really must “fix” the joint, leave it alone and do not attempt to fix the problem until the joint has become stone-cold. I repeat this warning in different words to stress this point: do not be tempted to “fiddle around” when the lead is still hot because it’s nearly ready to melt!

Let us assume you’ve dropped your blob of solder, hovered with the soldering iron and have and wiggled and rolled the solder around to the point where it has satisfactorily covered the whole area of the joint. You must immediately  pull away the soldering iron because you don’t want the leads to melt.

And finally, an opportunity to clean-up as you go. As soon as the soldering iron has been removed, count a “slow 5” to give the solder enough time to become solid but not long enough to allow the tallow flux to solidify. It is now safe to wipe the soldered joint with a paper towel or a clean rag. This will remove excess tallow and save you a lot of difficult cleaning work later.

If you forget to wipe away after your “slow 5” then don’t worry. Bring your soldering iron reasonably close to the joint for just long enough to re-melt the tallow then remove the soldering iron and wipe away. Your objective is to gently melt the tallow and not to re-melt the solder!

Remember to remove your little piece of cardboard (or paper).

Waterproofing and Strengthening

In this section please notice that I do not use the word “putty” because it is the wrong word and the wrong product to be using when we concern ourselves with the waterproofing and strengthening our freshly soldered leaded panels.

Leaded light cement smells a little like ordinary glazing putty but looks different. Leaded light cement is usually dark coloured and always has a sloppier consistency. Both smell of linseed oil but leaded light cement smells more of turpentine (or substitutes). Another difference is that putty stays soft for many months, if not years, whereas the cement dries and sets within days. So, dear reader, there really is a difference between putty and leaded light cement.

If you’re not doing much leaded light work then remember that the leaded light cement will slowly “settle out” in the tin over the course of a year or two into a hard lump of solids underneath an oily top layer. Despite this, I have found that even after a few years of settling it can be “revived” and made usable again, but it is time-consuming process poking, mixing and squidging the solid and liquid portions back into something usable. This may be useful to remember if you’re short of funds but have plenty of spare time.

It is also a hint that you should not buy more than you need. Or, as an alternative, perhaps we should make our own, storing the dry and wet portions separately, then mixing only what’s needed when it’s needed. Oh dear. The formulation of leaded light cement. It’s another area I’ve yet to chatter about.

For the moment, I just warn you not to blindly follow the recipes that some people are publishing on the Internet. As you might expect, some are sensible but some of them are well-intentioned but reveal themselves to be ill-conceived on closer inspection. If some lengthy chatter about formulations for leaded light cement is important to you, please prompt me to do this sooner rather than later.

Right, back to topic of waterproofing and strengthening…

The general plan of attack in this stage of construction is to force the leaded light cement into gaps between the lead cames and the glass pieces. With the gaps filled we achieve a single solid structure. Over the course of a few days the leaded light cement hardens and therefore stabilises the panel and increases its strength. Once hardened the cement also forms a waterproof barrier.

The best warning I can give you is to not get too enthusiastic, trying to force too much into the gaps, because it’s only going to start oozing out of the other side of the panel. All you’re aiming to start with is to fill the gaps on the “upper” side of the panel. Once the whole process of waterproofing and strengthening is complete on one side, you can then flip the panel over and repeat on the “other” side. The elapsed time is days, not hours!

DSCF3286 WaterproofingHere is a picture to illustrate what I’m now talking about.

Waterproofing is a messy process so use plenty of newspaper under your work. Cheap throwaway toothbrushes and nail brushes are recommended for forcing the cement into the gaps. It is better to use throwaway items than buying and cleaning expensive brushes because the hardened cement renders the brushes useless. Can you see how messy the little nail brush is in the picture?

Another tip is that you can also use a piece of glass to ‘push’ the compound into gaps but I don’t tend to do this.

I should also mention that leaded light cement is fantastic at finding its way into the smallest cracks, crazes, and deep recesses of textured glass surfaces. Never forget that the cement can destroy the visual appeal of the most gorgeous piece of “unsmooth” glass with a patchwork of mucky marks that are impossible to remove. Protect the surface of any glass that has such surface imperfections by whatever means are available to you so that the leaded light cement can not find its way into these defects in the glass. An adhesive plastic film should work nicely, maybe even self-adhesive labels.

If you’re careful and don’t randomly slosh the cement everywhere then it’s going to be easier to “clean up” later. To this end, try to keep the cement close to the filled-gaps and do your best to not get the cement on the tops of the lead cames. Look at the picture to see how I try not to make too much of a mess but wasn’t entirely successful.

When you have cemented one side of the leaded panel it’s time to add whiting (see below).

Be aware that the volatile ‘drying agents’ in the cement are smelly so ventilation is suggested. It’s not that these vapours are toxic, it’s that their smell can be quite intense and last for days.

Once the whiting has been added, leave the panel overnight, clean-up that side of the panel then attend to the other side of the panel.


Whiting is nothing more exciting than chalk powder and it needs to be sprinkled over areas where leaded light cement has been applied. An alternative to whiting is to use fine sawdust or fine wood shavings. Whatever you use, just remember that the aim is to “draw out” the oily part of leaded light cement.

Plaster of Paris and patching plaster have also been suggested as an alternative to whiting but I’d be wary of them because any hint of dampness may cause them to solidify on the surface of your glass, making the cleanup process harder. Let me know if you’ve tried these alternatives as I haven’t.

DSCF3288 WhitingHere’s a picture of a panel that has just had whiting added. It still looks nice and white but in a few hours it will start to look rather mucky. Notice that I’ve tried to put more whiting where there’s more leaded light cement and less where there’s (hopefully) only glass. Notice also that there’s whiting on top of the leads because there’s cementing “mess” to be dealt with on top of the lead work.

So, don’t be mean-minded with the whiting. Use as much as is needed. As a minimum at least try to get most of the whiting where there’s cement. In addition to drawing out the oily part of the cement, whiting also helps to clump together particles of excess cement and as such is really helpful in the “cleaning up” activities.

After a few hours the whiting starts to clump and look mucky. Now you may clear excess whiting off the glass surface carefully with a soft brush or a cloth but stay away from the leaded areas as they have not hardened sufficiently. Try and leave decent border (at least 2mm) around the leaded areas completely untouched. Carefully removing cementing compound from the tops of the lead cames is another task that can be started. Adding more whiting or shuffling “unused” whiting to where it’s still needed can also be done. So, at this stage our aim is to remove the worst of the mess without compromising the quality of the waterproofing or strengthening.

On the next day, no sooner, remove the 2mm borders carefully with a wooden stick, matchsticks, an All Nova tool or similar. This is where I mostly use used matchsticks. If you used enough whiting then the cement will have set sufficiently and this becomes quite an easy job. The clean-up process is all done when all the gaps between glass and lead are filled with cement and there are no stray lumps of cement on the lead cames or on the glass. Try not to under-cut the cames when cleaning away the excess cement because all it achieves is little water collection areas which are ideal micro-habitats that encourage algal growth especially in damper climates.

Once cleaned up, it will still take a few days for the remaining “drying agents” to evaporate out of the cement. As time passes the stink slowly subsides.


Some people suggest that soldered joints should be darkened to match the lead work. Zebrite is a commercial product that can be used to blacken the lead and solder and is normally used to blacken stoves. Zebo is an equivalent product that is no longer made.

My experience is that these products don’t really work very well, except on stoves. They hardly take to solder and aren’t much better with fresh lead. So an alternative suggestion is to patinate (ie use patina) these areas first.

Better still, in my view, is to not bother with this step. Allow the lead and solder to do their darkening naturally.


Here are a few miscellaneous things that I couldn’t sensibly put anywhere else:

An alternative to using a grinding stone or grinder to remove a burr from glass is to run a piece of scrap glass down the edge of the cut edge. Quick and good enough for leaded light work. Another handy trick from the days before electric grinders.

Smooth side outside and textured inside is the old general rule for glazing leaded lights. This is simply because single-glazed windows get dirtier outside than inside. However, this becomes questionable when the panel is part of a double-glazed window pane or embedded into a triple-glazed window pane. For indoor decorative pieces it’s a matter of design because you might deliberately want people to touch and experience the different surface textures.


I do not tend to get involved with the installation of leaded lights so only have a couple of thoughts to pass on.

Using glazing putty to mount a leaded light panel into a window frame has been a standard practise for many years. It works and there are no nasty side-effects. Our ancestors knew what they were doing.

By contrast modern squirty plastic “caulk” type fixatives should be treated with caution as I have learned from personal experience. By “caulk” I am thinking of the kinds of product that you would use to seal the gaps around door frames or around a bath or sink. Take care with these products and check the labelling to see what happens when they “cure”. If the product produces a vinegar smell as it “cures” a consequence is that it will be prone to provoke a white powdery surface patina of lead acetate on nearby cames. Lead acetate is a far greater risk to your health than the lead of the cames.

Sometimes a leaded light panel is added as an indoor secondary panel against an existing window. I have seen double-sided sticky black butyl tape being used to attach the perimeter of a leaded panel to the perimeter of the pre-existing glazing. A typical location might be the window pane adjacent to a door.

Health & Safety

Last but not least is the dreaded Health and Safety section. It’s a must because we’re working with lead.

Working with lead cames to produce leaded lights raises a number of heath and safety issues and some of them I’ve already alluded to. I will now elaborate.

A guiding principle in health and safety is that the elimination of a hazard is always preferred to doing something that reduces the effects of a hazard which in turn is preferred to the use of protective equipment to “hide” from the hazard.

Lead cames and particles of lead are not, in themselves, toxic. It is the compounds of lead that are what we should be most worried about. It is biological and chemical actions that turn lead into compounds of lead that you need to be most wary of.

Already mentioned is lead acetate from “caulk” that may arise when mounting and installing a panel. Lead acetate is a compound of lead. It is a white powderly “bloom” and easily inhaled or injested if you don’t take care.

Another source of lead compounds is through the action of sweat on our fingers reacting with lead when we handle lead came or solder. So, although touching lead is not very much of a hazard to your health, the ingestion of lead compounds produced by the sweat on our fingers is bad news. The transfer route that leads to ingestion tends to be lead came to fingers to mouth. So, before you try eating, drinking and smoking, stop working with the lead and wash your hands first.

Ingestion of particulate lead and lead compounds can be caused by airborne particles and I’ve already explained why I do not use wire wool on lead cames. So, rather than waste time and money using cheap ineffective face masks, eliminate the creation of particular lead by not using wire wood to clean up lead cames.

Although not directly lead-related, remember horseshoe nails and modern lead cutters that double-up as a hammer. Here you need to be careful not to cause puncture wounds and cuts. Puncture wounds and cuts must be covered with sticking plasters when working with lead or other toxic chemicals. Cuts and wounds are a fast and efficient entry point into your body.

If you’re a bit paranoid, you might consider using some rubber or nitrile gloves to minimise your contact with lead. But don’t let these gloves lull yourself into a false sense of security – remember to wash your hands after you take them off.

Lead poisoning is one of the oldest occupational hazards due to lead mining over many centuries so a word about exposure limits is perhaps needed. The first point to make is that different nations have different legislation so I can only generalise.

Lead exposure limits are unlikely to be exceeded if you’re an occasional hobbyist. The trouble is that workers only occasional exposed to lead, and hobbyists, are not really in a position to measure lead exposure without outside help. If you are in the least worried, try talking to your medical doctor, or your employer’s occupational health service (if you have one).

The group at risk is full-time workers who spend a lot of their time working with lead and traditional lead-based solders.  If you are an employee in a company where working with lead is a significant part of your job then your employer ought to be monitoring your lead exposure routinely through periodic medical assessments. I say “ought” rather than “will” or “should” because theory and reality are rarely the same.

The world is full of experts in Health and Safety and unfortunately a lot of health and safety is about subjective opinion rather than reasoned facts. Unfortunately this leads to experts that are, to varying degrees, ill-informed, paranoid, obsessive, irrational, deliberately biased or downright dim-witted. Somewhere amongst the cacophony of mixed messages is a reasonable and rational basis on which to live our lives!

If you think I should do a blog on Health and Safety that identifies some of the hazards and risks of our activities and translates them into advice that is hopefully more balanced, rational and helpfully practical then please tell me that it’s something you want sooner rather than later.

A Topical Postscript

And finally, on the subject of Health and Safety, you may already be aware of what’s happing in Oregon in the USA.

I note with concern that “the authorities” in Oregon are behaving irrationally and badly towards glass producers Bullseye and Uroboros. You will find more information in the news releases section at the Bullseye web site. It makes interesting reading because it relates to to toxic metal emissions from furnaces.

The recent announcement by Spectrum that they are shutting down makes this even more worrisome for our chosen career or hobby.

This health and safety madness in Oregon reminds me of a quote attributed to Voltaire:

It is dangerous to be right when those in power are wrong.

Or perhaps this one from the painter John Constable:

We see nothing until we understand it.

Bye for now, dear reader. Thank you for visiting my blog.




Posted in Cartoon design, Flux, Glass Cutter, Lead cutter, leaded light, Leaded light cement, Putty, Solder, Soldering, tallow, Whiting | Tagged , , , , , , , , , , , , , , , | 4 Comments

Repairing a Broken Mould

Today’s chatter describes an attempt to repair a broken ceramic mould so that it can be brought back into useful service. The repair process takes time and patience but it might help you salvage a expensive broken clay mould.

If you’re from the USA then today’s extra learning is that when I write the English word “mould” you should pretend you saw “mold” and not confuse it with the Welsh town called Mold.

Some Background

Many years ago, when I had more teeth and my hair was pigmented, I was still naïve in all matters relating to fused glass. I bought a little teardrop mould that would fit into a recently purchased microwave kiln thinking that it would be fun to make some fused glass teardrops.

What I didn’t appreciate in those days was that a microwave kiln is a harsh beast with rapid heating and cooling that was going to be a problem for the mould. All I can say in my defence (or defense in you’re in the USA) is that there was no information sheet with the mould giving me a recommended kiln schedule which might have served as an implicit warning that trouble was ahead.

As I now know disaster was entirely predictable. The mould cracked into three pieces on my very first attempt to use it. So, for several years, the broken mould languished unloved but not forgotten in its box until I could figure out what to do with it.

Hindsight is a good teacher and lucky for me it was not an expensive mould.

The Underlying Idea

I know from previous experiments that a glass kiln may not be able to reach the high temperatures required to fire clay to completion, to the satisfaction of a potter, but can be processed in a glass kiln sufficiently to make a usable mould. The resulting moulds were not as strong as a “proper” ceramic mould but have shown themselves to be perfectly adequate for use with glass.

I therefore reasoned that it might be possible to use some clay slip (of thick double cream consistency) to “glue” the broken parts of the mould back to together then strengthen the joints by firing the repaired mould in my glass kiln. I was right.

The Outcome

DSCF3312 Mould RepairHere’s a picture of my repaired mould. It is a small Slumpy mould and has been repaired by the method I shall now describe for your. You can still just about see where there used to be cracks and you can see I still need to give it a final clean-up.

You’ll have to take my word that it’s now good enough to be brought back into use!

I hope you have equal success but if you have any extra good ideas to contribute then please let me know and I’ll update this blog with your new information.

The Repair Process in Outline

If you’re in a hurry or can’t cope with my copious chatter, here’s a summarised description of the repair process.

  • Clean mould, removing kiln wash and other contaminants
  • Wet mould then use thick clay slip as a glue
  • Clean away excess clay carefully
  • Allow mould to dry, using elastic bands (etc) to hold pieces in place
  • First firing to strengthen the repair joints
  • Second round of repairs with clay slip to address remaining defects
  • Second firing to make mould as-good-as-new

Read on if you’re still interested!

The Repair Process in Detail

The first step in the repair process is to thoroughly clean the mould, attempting to remove all traces of kiln wash, dust and grime. For this I used a single-sided razor, a kitchen scouring pad and copious amounts of water. In effect, this task is much like cleaning a kiln shelf before re-applying kiln wash. If you’ve unfortunately succeeded in dropping your mould before it was ever used then this step will not be needed.

If you’re previously prepared the mould with a boron nitride spray then you will not be able to completely remove the boron nitride. Do not despair. Try your best and stay hopeful as the coating should only be at the outside surface and not at the edges that will be “glued” with clay.

You will need some thick clay slip. I used exactly the same cheap clay for the repairs as I used for my previous mould-making experiments even though the clay was supposedly not suitable for use in a kiln! I mixed just enough water and some clay scraps to form a smooth gloop with a consistency of thick cream.

When you have a nice clean mould, pop it into a bowl of water for a few minutes. It is going to be easier (and the results will probably be a little stronger) if you “glue” the pieces of mould together when they are wet because dry pieces of mould will rapidly such the water out of the clay slip making it too stiff to accurately and neatly “glue” the pieces of together.

Next comes the gluing step. As you would with ordinary glue, apply a thin layer of your clay slip around all the edges that need joining. Gently push together all the broken pieces, trying your best to accurately place all the pieces together. Now is a convenient time to wipe away the worst of the excess clay slip that squeezes out. This step is made easier by having previously wetted the mould pieces!

Do not worry too much if a few little shards of mould have been lost, or the some of the pieces refuse to sit exactly where they ought to. This can all be resolved later!

With all your pieces of mould “glued” together it’s time to ensure that nothing moves until the mould has dried off. I used elastic bands but any other method that keeps everything stable can be used. Tight joints are what we are aiming for.

At this point a little gentle washing with a damp sponge (or fingers) can be used to remove some more of the excess clay. But be careful you don’t cause the clay mould pieces to fall apart or move. Do not worry if you can’t clear away all the excess. This can be done later.

Now leave the mould until it is completely dry. I think natural drying is the best choice because it allows clay minerals to “migrate” into all the tiny gaps which we are hoping will result in a stronger repair. Another reason is that using damp sponges and cloths in the next step are a little less prone to cause the repair to fall apart!

When the mould is dry, remove the elastic bands (or whatever you used) and inspect the mould. If any little holes need filling then now’s a convenient time to fill the holes. Leave the mould to dry-out again if you just did more repairs.

If there are any areas where there is an excess of clay then try to remove the mess with a damp sponge, dampened paper, or whatever else you think will work. You may find that dental picks, lollipop sticks and single-sided razors are also useful. Fingers are an amazingly useful tool as well! I remind you to be careful to not cause the ceramic mould pieces to move or fall apart. Unfired clay is not a strong glue and when you add water the clay “glue” suddenly gets even weaker. A strong hint for this step is not to use too much water!

Whenever you “re-work” the mould repair and cause it to become dampened, add those elastic bands and again leave the mould to dry out completely.

Do whatever is needed, again and again, until you are happy that your repairs are about as good as you can get. But do not obsess about joints that are not quite right or that there may be a little hole that needs filling because this can also be addressed after your first firing.

You’ve now got the point where you’ve done your best with the repair. Well done. It’s a messy and fiddly job and you probably had to do it several times to get it right. Patience is a virtue! Now is the time to convert the weak clay glued joints into a stronger mineralised clay joints.

For my first firing I happened to be slumping some bottles and there was an unoccupied space on the kiln shelf to fill, so that’s what I did first. Slumping at around 700 degrees Celsius is hardly a full fuse but I found that even this low temperature was enough to fire the clay enough to begin to mineralised and form an acceptably strong repair. Another advantage of this firing schedule was that it was conveniently slow and gentle.

After this first firing I found that some of the original mould pieces were not aligned exactly. I could feel the joints with my finger nail and decided that they would result in unsightly lines on anything made in this repaired mould. I also spotted a tiny little depression where three piece or mould met. So, the obvious answer was to attempt a “improvements” repair.

The improvement repair was nothing more than to apply a little more clay slip to areas that needed them. Again I wet the mould before applying more clay slip but this time there was no need to worry about the mould falling apart because the joins were already quite strong. Again, you may need to do this several times until you’re happy with your final repair attempts.

With the final repairs done, leave the mould to dry out (yet again) and then put it back into the kiln to produce what we hope will be a good-as-new repair.

Job done. An expensive but broken mould can be brought back into service!

Some Extra Notes

You may be concerned about the strength of the joints and that a ceramic mould is being repaired using clay at a temperature that is much lower than a potter would have been used to produce the original mould. Let me explain my understanding and the consequences…

Although I am not a potter, I am aware that clay undergoes various predictable chemical changes at different characteristic temperatures and that each of these chemical changes happen only slowly. Each of these chemical changes we can think of as progressing the clay from a weak substance stepwise towards a very strong ceramic substance. This also explains why potters use long and slow schedules compared to our “in and out quickly” schedules. Forming a strong crystalline structure is good for pottery but is bad for glass work! Yes, I’m thinking of devitrification!

So, by firing our repairs in a glass kiln at a relatively low temperature and for a relatively short time we only cause the clay repair to incompletely take the first few steps of the pottery firing process. From this I think there are three practical consequences:

  1. We have not fired the repair to a high enough temperature. This means the resulting repair is not as strong as the original ceramic mould because the clay has not been converted to the same “final” chemical substance that the original ceramic mould is made of. This means we have to handle the repaired mould with just a little extra care.
  2. We have not fired the repair for long enough. This means the resulting repair is not as strong as the original ceramic mould because the clay was probably not in the kiln long enough to allow achievable chemical changes to be happen completely. This leads to an interesting speculation that the repaired mould may get a little stronger after being used a few times. But again, it means we have to handle the repaired mould with just a little extra care.
  3. By under-firing the clay minerals of the slip have not become as hard and durable as the original mould which, conveniently for us, means that our repair is still soft enough be sanded or scraped to address remaining defects.

When All Else Fails

If you’ve done your best but the repair fails or is not to your satisfaction then I offer a final thought…

If you can repair the mould sufficiently to achieve a close approximation to the original mould then you have something that could be used to make another mould. As they say, there’s more than one way to skin a cat.

Go for it. At the very worst you start with a broken mould and end up with a broken mould!

Posted in Experiment, Microwave kiln, Money-saving ideas, Mould, Recycling, Repair | Tagged , , , , , , | 2 Comments

Glass Devitrification – Look Closer

I want to chatter about glass devitrification but there’s far too much to say in a single posting. Therefore I’ll start the topic by talking about correctly identifying devitrification. I will leave further related topics for future postings.

As is usual, I’ll be walking you down a meandering path that others do not take.

In the Mood

I’ll start with a quote from my previous posting, Lubricate Your Cutter Wheel because it’s the motivation for this blog posting and several more to come:

A clean cutting oil is a simple hydrocarbon mixture which will cleanly evaporate or “burn off” within a kiln – but we are told this can cause devitrification. However the use of other “contaminants” such as Glastac or White Glue (PVA) are routinely used and also “burn off” – but we are told these are not a risk for devitrification. This all looks rather self-inconsistent to me. We want facts not superstition and hearsay!

I am also motivated by encountering internet forum postings that leave me with a suspicion that there are many people working with glass who don’t always identify devitrification correctly.

Looking and Touching

To use more than one of our senses, when it’s to our advantage, may seem obvious but try reading what people say in the internet forums and decide for yourself. Do we use more than one sense when describing what we think might be devitrification? I suspect not.

I therefore want to suggest that we must consider how the glass looks and feels before we decide whether a problem is devitrification or not. I say this because there are things you’ll see in glass that look like devitrification but do not feel like devitrification.

Descriptive Terms

We often see words like “glossy” or “shiny” in contrast to words like “scummy”, “white”, “cloudy”, “grey”, “hazy” or “misty” to describe whether glass has devitrified or not. I’m sure you could suggest other words as well, but now consider how often we use words like  “smooth”, “rough” or “gritty” or find them in descriptions within the Internet forums. I think that words that describe how glass feels to the touch are rarely mentioned.

Pass the Sugar

Perhaps the best way to understand what devitrification is, and is not, would be to use a more familiar material and relate that to the micro-structure of glass that is “good” and has “gone wonky”. And sometimes it’s the simplest of analogies that teach us the most and I hope what follow makes sense in your mind.

I’d like you to consider how individual grains of sugar look and feel and then consider how they look and feel when they are “bunched together” in the form of a sugar cube. Notice that I ask you to look and feel the sugar. Put your hand into your sugar bowl. Fiddle with a sugar lump when you next visit your local coffee shop. Study them closely.

Do you feel the roughness of individual grains of sugar as well as the rough surface of a whole sugar cube? The roughness of both comes from the “pointy ends” of the sugar crystals. It is the same kind of rough “pointy ends” of regular crystals (as opposed to amorphous crystals) that you are feeling when you run your fingers over a devitrified glass surface.

Did you see that individual grains of sugar are quite transparent and are quite shiny when you look at them individually (blow off the sugar dust if necessary!), but notice also that the sugar grains in a sugar cube tend to be opalescent, white, dull and cloudy? The clarity of a single sugar crystal is expected because light is not being scattered around and we can liken this single crystal of sugar to the single amorphous crystal of a nice “good” piece of glass. The loss of clarity that results in the white, dull and cloudy effect in the sugar cube is a consequence of light passing through many sugar crystals, scattered in many directions. This scattering of light in the sugar cube is exactly what you also see with devitrified glass because regular crystals have begun to form in devitrified glass.

So with our sugar analogy representing the way devitrification causes light scattering in mind, I now want you to explore another analogy for something that is sometimes mistaken for devitrification.

Extending the Analogy

I now want you to think about what’s between the crystals in a heap of sugar to extend the analogy we’ve been talking about. I think you’ll agree it will be lots of interconnected tiny pockets of air. If you’re not following me then think about the same situation at a larger scale – a pile of bricks or pebbles. Yes. Between the crystals of sugar are little pockets of air. It doesn’t matter how big or small those sugar crystals are, they always seem to have little pockets of air between them.

Now I want you to imagine the cooking process by which you might convert some granulated sugar into a boiled sweet. You’ll need to add a little water. But not too much food colouring or flavouring. After boiling, the sugar solution gets thicker and eventually the resulting sweets will be shiny and smooth on the outside and completely transparent inside. For the purposes of our analogy we used water to fill the gaps where air bubbles used to be. So you end up with boiled sweets that do not contain air bubbles and they’re crystal clear. By keeping bubbles of air out of our glass we keep it nice and clear.

I want you to now contrast the outcome of the boiled sweet cooking process with something you may have encountered before –  a bowl of sugar left for a long time in a damp environment. The same can happen with common salt as well. You should be able to imagine millions of little sugar crystals that have become damp and that the dampness allowed the crystals to stick together. Here we had enough water to connect the crystals together at some of their edges but not enough to “fuse” them together into a single solid block. We still have little pockets of air between the crystals yet it is a single block of sugar. In our fused-together heap of sugar we notice lots of light scattering that results in a white, dull and cloudy effect.

If you’re “on the ball” you’ll realise that the damp sugar analogy is exactly the same as the sugar lump analogy. What I want you to notice is that in the sugar lump analogy I was focusing your attention on sugar crystals in close proximity, but for the damp “caked” sugar analogy I was focusing your attention on the little air pockets between those same crystals.

There are two things we’ve learned that I want you to ponder over for a moment

  • A heap of glass crystals in close proximity will scatter light
  • A mass of tiny bubbles in close proximity inside glass will also scatter light

And, as we’ve learned the visual characteristics of devitrification seems to be the consequence of scattered light. So, why have I also be talking about little bubbles?

It is now time to apply the concepts of “crystals” and “bubbles” to real examples.

Wonderful Micro-bubbles

If you have never fused a heap of clear powder frit then now’s the time to try. At the same time you should also try fusing a heap of course clear frit. Even if you’ve never done this you’d not be surprised to find that the coarse frits fuse together to produce a clear lump of glass. What may be a surprise is that the clear powder frit fuses together to form a lump of glass that is white, dull and cloudy.

What’s happening with the clear powdered frit? It has been fused together and now resembles our analogy for a heap of caked sugar.

It may look like devitrification but what does it feel like? It feels smooth. The smooth surface tells us we’re touching a smooth amorphous glass surface which means it is not devitrification. The bubbles beneath are the causing of the white, dull and cloudy effect by light scattering.

If you have never used your glass grinder on the edge of a piece of glass and then fired the glass then now’s the time to try. If you have, you’ll have probably noticed a white, dull and cloudy effect that looks like devitrification. Indeed, I’ve seen many people describe this effect as devitrification on Internet forums, Facebook and even in conversations with me.

It  may look like devitrification but what does it feel like? It feels smooth. The smooth surface tells us we’re touching a smooth amorphous glass surface which means it is not devitrification. There are bubbles beneath that are the causing of the white, dull and cloudy effect by light scattering. The ground edge created a very roughened surface that would resemble a vast mountain range if you were a tiny microbe. When you fire the glass the mountains collapse, flop over and distort. As they do so, they trap millions of little bubbles of air.

DSCF3037 Grinder and FritLet me show you a picture of a “test piece” in evidence of what I’m saying.

On the top of the clear glass was a heap of clear powder frit that now looks white. You can’t tell, but I know it feels very smooth. The opacity is the consequence of micro-bubbles and is most definitely not devitrification. Imagine how a shallow heap of clear powder frit might behave. Would it be white or perhaps merely cloudy? Better still, do your own experiments!

On the side of the glass, nearest to you in the picture I used my (coarse) glass grinder. After firing you can see a cloudiness along the edge. You can’t tell, but I know it feels very smooth. Again the opacity is the consequence of micro-bubbles and is most definitely not devitrification. Imagine how a finer grit might behave (eg after using a diamond pad). Better still, do your own experiments!

DSCF3060 Xs OverglazeMy next example is a green opal blob made from scrap non-fusing glass. I made it especially for this blog.

This green opal blob suffered from a bad dose of devitrification along the line at the left and thin patchy devitrification here and there on the top on first firing. I knew it was devitrification because it looked and felt like devitrification. What I did next was quite deliberate, so that I could give you another example to consider.

I deliberately over-dosed the surface with an large excess of devit spray. What you need to know is that the devit spray I used contains very finely powdered clear glass and you’re likely to be using something similar. I know it contains very fine clear glass powder because the manufacturer’s MSDS safety data sheet tell me it does. The glass powder in devit spray is much finer than you encounter with powder frits.

Notice that the over-application of devit spray has produced an effect that looks like devitrification. It is similar to what we just saw with a heap of powder frit. The line down the left edge that really was devitrified now looks even worse. The top surface also looks worse. Although it might look like devitrification, I know from my sense of touch that the glass surface is now very smooth and glossy. It is not devitrification – it’s micro-bubbles again!

Nasty Roughness

DSCF3019 DevitI should now give you an example of real devitrification to complete the picture. You will see the dreary looking blob of dark opal glass in the picture.

You will immediately see the speckled effect on top. You will also notice that those patches are white, dull and cloudy. What you can’t tell is that the surface feels very rough. This is nasty dose of surface devitrification.

Something else to notice is that the devitrification is patchy with some of the patches being very small. This is a characteristic of devitrification. It starts very small and grows and grows.

DSCF3010 Spiky DevitAnd here’s another example of devitrification. It was made from a small stack of white scrap non-fusing glass. If nothing else, it will show you that devitrification is not always just a scummy surface defect.

Can you see the dull white surface? Can you also see some “spikes” sticking out from the surface? To the touch it is really rough and gritty. Those spikes are also rather sharp!

What’s happened here is that the non-fusing glass has quickly devitrified in the kiln, so quickly and to such an extent that the crystalline structure of the devitrification has stopped the glass changing completely into the more usual rounded shape. This is an amazing accidental one-off that I’ve never seen before or since. I doubt I’ll ever see it happen again so I will keep this little blob as a piece of “special treasure”.

Why and how devitrification happens will be the subject of another blog posting but in the meantime you might like to read up about nucleation.

Look Closer

There are two tools I found useful when I began exploring devitrification. One is a cheap microscope and the other is a dental tool. The remaining tools were, of course, my eyes and fingers.

DSCF3058 Dental ToolThe dental tool, shown in the picture, is useful because the sharp point can be used to hunt down little defects on a glass surface. In this sense it is nothing more than a miniature version of a finger. You can also use it to hear the roughness of a surface when scraping.

DSCF3054 Microscope2.pngThe microscope I used was very useful, even though it is sold as a child’s toy. It has enough magnification to easily distinguish “scaly” crystalline devitrification from “bubbly” effects that are not devitrification. There are many other designs that are as cheap and equally good but you’ll see what I used in the picture.

Raiding a child’s toy box is perhaps the quickest and cheapest way to find a “toy” microscope. Giving your child a similar “toy” microscope for their next birthday would also be a good idea because then you can “borrow it” after they’ve lost interest in it.

This particular microscope is small, lightweight and fits into a pocket. It has a “zoom” that offers magnifications from 20x to 40x which is perfectly adequate for our purposes. The focus can be varied and it has an optional white LED light to illuminate what you’re looking at.

The black plastic attachment converts this microscope from being a “dissecting microscope” into a “slide microscope”. For our purposes we want a “dissecting microscope” so this slide attachment was not useful for my glass investigation work.

I did try to use a 10x magnifying glass of the type field biologists commonly use but the magnification wasn’t sufficient in my opinion. But do try one if you happen to have access to one – 10x is better than nothing more than 1x magnification!

Further Study

For a very nice summary of what devitrification all about, have a look at the Encyclopædia Brittanica site here .

You can read more about what an “amorphous solid” is here  and you might like to read up about the nucleation  process that triggers devitrification.

Why and how glass devitrifies, and what you can do about it, will be the subjects of future blog posting.

Do it Yourself

This posting has been rather practical in its outlook so it must be time for me to prompt you into action. Here’s your homework:

  • First, find a nice little oblong scrap of clear glass that’s suitable for use in a kiln, making sure that it is clean and has has no ground edges or signs of devitrification.
  • Next, grind three of the sides of the scrap of glass. Use a coarse grinder along one edge, then use two other grades of diamond grit pads (if you have them) on the next two edges and leave the final edge un-ground.
  • To one side on the top, add a small heap of clear powder frit.
  • To the other side on the top, add a big glob of undiluted PVA and allow it to dry.
  • Fire on a full fuse schedule (or a profile fuse) when you’re next using your kiln.
  • Inspect the top and sides of the fused glass, remembering to look and feel.
  • Confirm in your own mind whether or not I have not been talking rubbish.
  • Think about how your discoveries might change your glass working practises.

As a budding scientist you should be able to predict what will happen even before you even try the experiment:

  • The excess of PVA will burn off but will cause pitting on top of the scrap glass. It will be rough to the touch and will look “cloudy” or worse.
  • The heap of clear powder frit will fuse together but trap micro-bubbles of air. It will be smooth to the touch and will look “cloudy” or worse.
  • The three ground sides will show differing degrees of micro-bubbles that relate to how coarsely the edges were ground. They will be smooth to the touch and to varying degrees they will look “cloudy”.
  • The underside of the scrap of glass as well as the fourth side will be shiny and smooth to the touch and you will see no problems. These are your “controls” and should not devitrify on their first firing, nor should there be any micro-bubbles.

Remember to investigate how the glass looks and feels to understand the difference between devitrification and micro-bubbles. If have an opportunity to look at the top and edges with a microscope you will instantly recognise the difference.

You may reach a conclusion that the pitting caused by the PVA is merely “damage” but not devitrification. The answer to this conclusion is to subject the piece of glass to further firings and observe what happens to the pitted surface. If it continues to be rough to the touch then it was devitrified and will therefore remain devitrified. If it becomes smooth to the touch then it gets “repaired” which suggests the PVA did not cause devitrification.

Next Time

I’m not finished with devitrification so I promise I’ll address another devitrification topics in future postings. Exactly what that topic is I’m not sure. All I hope is that you’ll find them all useful.

I wish you a prosperous and happy 2016 and thank you for following my blob.

Posted in Devitrification, Experiment, Frit | Tagged , , | 5 Comments

Choosing and Using an Oil-Filled Glass Cutter

This article is the consequence of a rather surprising feedback comment in March relating to the purchase of a Toyo oil-filled glass cutter left at the Tempsford Stained Glass web site.

Tempsford Stained Glass were given 4 out of 5 stars and the following feedback:

Impressed by the quick delivery of this product but there was no information about how much oil to use.

To begin with I guffawed with laughter but later I began to understand that sometimes it is the little things in life that cause us trouble and confusion. My experience of Tempsford Stained Glass is 5 out of 5 so I dedicate this article to the author of that feedback comment.

A companion posting to this one is Lubricate Your Cutter Wheel where I chatter about the different lubricants people are using with their glass cutters.

The Olden Days

I will deliberately restrict what I write about the “bad old days” because it’s not so relevant to what we’re doing nowadays. Nevertheless there are some aspects that are still applicable.

Roll the clock back a century and your glass cutter would be a small diamond (or sapphire) glued to the end of a stick. Losing that little diamond could be a problem! You will find out more about such glass cutters if you pay a visit to the Gutenberg Project and look for a book called Stained Glass Work: A text-book for students and workers in glass by Whall. It is free, available in a variety of electronic formats and is a fascinating insight into the profession almost exactly a century ago.

As we move forward in time we get to the still-commonplace cutters which all have a small wheel at one end, often some “teeth” just above, then a handle and finally a ball at the top. A quick explanation for the teeth and ball is needed because their purpose is not obvious to a novice…

The ball at the top is used to “help”, “chase” or at least “start” a score line cracking by means of tapping underneath the score line. It’s hard to describe and demonstrate the process in text, and it takes some practice to achieve reasonable results reliably, but at the end of this article I give you a web link to understand the tapping method by watching a video (or three).

Incidentally, not all glass cutters have the ball at the top. Have a look in eBay, searching for “Shaw glass cutter” for examples of these traditional cutters. The “blue Shaw cutter” is, I think, a popular first choice. You’ll also see from the picture in this posting that I have a couple of modern glass cutters that do not have this ball. You will find a link at the bottom of this posting where you can see others and even watch a short video about glass cutters.

The teeth of a glass cutter were particularly useful in the days before glass grinders and grozing pliers of the kind we use nowadays. The teeth allowed the glass worker to “nibble away” the edges of the glass piece. The rough edge produced by this method is not a problem for traditional leaded lights but often will be for the copper-foiled method.

The differently sized gaps between the teeth allow for different thicknesses of glass or different techniques. The only time I have ever seen anyone use these teeth was on television where an “authentic” restoration of a stained glass panel was being undertaken.

And finally, when the glass worker got their glass to about the right size they could then make use of a scythe sharpening stone – something you can still buy from good stained glass suppliers. You should realise that nibbling the edges of a piece of glass with those teeth and using a scythe stone are time consuming and “risky” compared to the use of modern tools. They needed to be good at their craft in those days!

I should perhaps mention that glass cutters with a stainless steel wheel wear out quickly and tungsten carbide wheels last longer, for reasons explained in my previous Lubricate Your Cutter Wheel posting. Some have replaceable wheels and some do not.

And it may also be useful for me to mention also that you also need an oily rag (I have one in a little tin) or a little pot of cutting oil to lubricate these cutters before each use.

You can still get these “traditional” cutters and in the country where I live the “Shaw”  brand is still quite popular. The traditional cutters still get used in some specialised tools such as circle cutters.

But, if you’re new to stained glass I recommend you jump straight to using a “modern” tool – an oil-filled cutter. This is not to say that a traditional glass cutter will not be useful but you’ll find it easier and more convenient to start with an oil-filled cutter.

Oil-Filled Glass Cutters

DSCF2900 Glass CutterOn the right you will see a picture of most of the common styles of oil-filled glass cutter available today. I will make some comments about each one in turn.

At the left is the cheapest of my glass cutters. It is from China and you can see it has no ball at the top and is slowly leaking cutting oil where the wheel is. I have used several of these cutters (and have given a few away too) but not all of them leaked like this one. This glass cutter is half full of oil and to fill it you have to unscrew the wheel-end of the cutter. The only problem I have ever found is that the lack of a metal ball at the top means that I can not use it to break glass using the “tapping” method – something that I recommend you only use when absolutely necessary because it tends to cause “wobbly” breaks, sharp “flares” and other problems when done badly. If you are strapped for cash then this is a perfectly good modern glass cutter to begin with.

Perhaps the most popular oil-filled cutter is the “standard” pencil-grip Toyo cutter (second from the left). I have found this cutter to be very reliable and long-lasting, it doesn’t leak, it holds a decent amount of oil (and is almost full) and the metal cap can be used for the “tapping” method of breaking glass and it is this cap you must remove to add more oil. This is the cutter I use most of the time. But, some people, particularly those with limited strength or painful ailments like arthritis, may find the next two cutters more usable.

The third from the left is a K-Star pistol grip cutter and is of a similar style to a Toyo pistol grip cutter. This cutter has a massive capacity for cutting oil and the one in the picture is about half full. Notice that there is a ball at the end of the handle for breaking glass using the tapping method and it’s this ball that you remove to re-fill the reservoir. I must confess that I don’t use this cutter very often because it “feels wrong” when I hold it and use it. By contrast, a friend with arthritis prefers this style of cutter because it does not hurt her wrist.

On the right of the picture is a tiny little cutter which nestles between your thumb and pointing finger. It is the Toyo Thomas Grip cutter. Notice that this cutter has a very small capacity oil reservoir and no tapping ball. Unscrewing the top of this cutter allows you to re-fill the oil reservoir. I don’t often use this glass cutter but I do find it particularly useful for curvy shapes.

Cutting Head Sizes

Did you notice that the Chinese cutter had a “wider” cutting head and that the other three were much shorter in profile?

A reason to choose a wider cutting head is if you mostly cut straight lines, simply because there’s a long surface along which the cutting head can more accurately slide along a ruler edge. For curves and free-hand work the shorter cutting heads are more convenient, not only because they can follow a curved ruler edge more accurately but also because they just seem to “feel right” -surely a completely irrational subjective reason!

Cutting Head Replacement

If you find your glass scoring is getting unreliable and the glass cutter has been used for a long time then it may be time to use a replacement cutting head. They cost almost as much as the whole glass cutter but your savings will come from producing fewer bad breaks and in turn less scrap glass!

At the bottom left of the picture you will see a replacement cutting head. It has a screw on the side. To replace the cutting head you unscrew and remove the old cutting head and then fit and re-screw the replacement with the screw pointing “forwards”. Nothing could be simpler.

Oh, and save the little screw before disposing of the old cutting head – you never know when you might need it!

And finally, a word of caution – the oil’s wicked to the cutting wheel by a little thread-like wick. Don’t remove the wick or the cutting wheel will either not get lubricated or the oil will simply flood back out.

An example replacement cutting head is shown that the bottom of the picture. Be sure to buy a replacement head that’s suitable for your cutter!

Filling an Oil-Filled Cutter

How you put oil into an oil-filled cutter depends on the model. The Chinese example (on the left) can be re-filled by unscrewing the cutting head and filling the reservoir with cutting oil. The two examples (in the middle) can be re-filled by unscrewing their ball-shaped caps. The little cutter on the right can be refilled by unscrewing the “handle” part at the top.

To avoid spillage and waste, use a cheap disposable pipette or syringe, for which you’ll see an example at the bottom right of the picture. Fill the cutter almost to the brim or just add a little. It’s your choice.

If you find the cutter has started to leak, dismantle and reassemble the parts. Some cutters have little rubber ring seals – check they are not broken.

Choosing a Cutting Oil

You have a choice of whether or not to use a cutting oil, as well as a choice as to what to use as your cutting oil. Here’s a quick summary:

  • Petroleum-based oils – often kerosene or paraffin or a mixture
  • Vegetable oils – beware of oxidation causing gumming-up
  • Water-based – supposedly “environmentally friendly”
  • Dry cut – some people don’t use any lubricant

You can either buy an expensive “glass cutting oil” thinking (or being told) it is somehow special or better, or you can use a “generic” cheaper alternative that is probably the same thing. Have a look at my Lubricate Your Cutter Wheel posting for a detailed discussion about who’s using what, why they use it and much more!

Other Resources

Don’t trust me to tell you everything and don’t trust my opinions as being the best. Do some more research. For example, here are a couple of nice places to visit. Other people’s opinions also matter, and the videos are worth watching.

And here is the first of a series of videos about tapping score lines. I could be argumentative about the terminology used sometimes but I will not be so because they’re nice helpful videos. I would only comment that I find it’s accuracy of the tapping rather than the softness of touch that makes for decent score line breaking by the tapping method.

Until Next Time 

Thank you for reading this posting. I hope you found it useful or at least interesting.

My next posting will probably explore devitrification because I see plenty of people on the Internet seem to be confused about what devitrification actually is (and is not).

I don’t have all the answers, but here’s a teaser from my previous posting to get you thinking:

A clean cutting oil is a simple hydrocarbon mixture which will cleanly evaporate or “burn off” within a kiln – but we are told this can cause devitrification. However the use of other “contaminants” such as Glastac or White Glue (PVA) are routinely used and also “burn off” – but we are told these are not a risk for devitrification. This all looks rather self-inconsistent to me. We want facts not superstition and hearsay!

Posted in Cutter Oil, Cutting Oil, Glass Cutter, Lubricant | Tagged , , , , , | 2 Comments

Lubricate Your Cutter Wheel

I did plan to write about glass cutters but got side-tracked by comments relating to”cutting oil” and suggested alternative whilst browsing around on the Internet. I promise to come back to glass cutters at some future date.

Sorry, but there are no exciting pictures of cutting oil in today’s blog posting!

Who’s Using What and Why

After meandering around the Internet I found a wide variety of liquids being used with glass cutters. Some of the places I visited include the Stained glass Town Square forum where you will find a discussion that caused me to make this blog, a comment in the Dendroboard forum, some good, bad and ugly advice all in one place at Stained Glass Town Square (again) and the typically dodgy advice and guidance at Yahoo Answers. I encourage you to search for more.

As one commentator points out, “Professional glaziers have been dipping their cutters into oil for over a century” so we can assume that there must be some rational reason for using a lubricant when cutting glass. A completely plausible explanation for kerosene being the traditional “cutting oil” is that “back before electric soldering irons, a glazier would use a kerosene lamp to heat the soldering irons, so there was always a supply of kerosene handy in the studio.

Although kerosene evaporates cleanly and doesn’t gum up a glass cutter it does have the problem of producing a persistent odour that can cause nausea and headaches for some people.

Commercially-made “cutting oil” is very popular and seems to come in two distinct forms – either a mineral oil or a water-soluble formulation. I’ll talk about them both, in turn.

The “usual” cutting oil that you may have purchased from a stained glass suppler is probably nothing more than white mineral oil according to the MSDS information I’ve looked at. The term “white mineral oil” is deliberately vague and is synonymous with both “light petroleum distillates” and “heavy petroleum distillates”. This means you’ve been buying something that is paraffin at the heavier end of the scale, tending towards kerosene at the lighter end of the scale. If you remember your High School chemistry then you may recall fractional distillation as being the method by which these mineral oils are produced from crude oil. If you’re really “on the ball” you may also remember catalytic cracking as well!

Therefore, any petroleum-based oil with a viscosity that is “about the same” as “white mineral oil” is a rational and reasonable substitute for commercial “cutting oil”. At the heavier end of the scale is the likes of 3-in-1 oil, which does appear to be used by some people, though this strikes me as being rather viscous. This observation seems to be supported by someone else using 3-in-1 oil who says they add some “Varsol” (what ever that might be) to thin the oil. Heading down the scale of viscosity are people using mixtures containing paraffin (not so viscous) and kerosene (least viscous) in products such as tiki-torch fuel. Other “light oil” products being used that are very similar include sewing machine oil, bicycle chain oil, lamp oil and baby oil.

All this might explain why people who prefer kerosene will also suggest that “cutting oil” is too viscous and does not wick properly in oil-filled cutters. However, other people complain about their cutters leaking which suggests the exact opposite. My guess is that the problem is not only the cutting oil but the condition and “brand” of the cutting head – I have never had a problem with leaking Toyo cutters but do with a cheap Chinese equivalent.

There is also a synthetic lubricant being sold. It is supposed to be water soluble and “environmentally friendly”. Apparently it washes away easily with water so that your copper foil will stick better. So far as I noticed on the Internet, nobody said that used this kind of lubricant. The manufacturers safety data sheet (MSDS) reveals a formulation based on ethylene glycol, diethylene glycol and water. This explains why it is water soluble.

There are also a few “unusual” choices. WD40 is mentioned by one person and water is mentioned by another. Although water might seem strange, it is implicitly involved in the “rubbing” of spit into score lines by some people (more about this later) and is contained in the newer “environmentally friendly” cutting liquid. Vegetable oils (such soya or corn/maize) have also been used though there are warnings about “gumming up” being a potential problem.

Last, but not least is the use of nothing at all as a lubrication. A fair number of glass workers seem to use glass cutters without any form of lubricant, sometimes giving a rational reason for doing so (such as keeping the glass clean) but often the justification is absent or irrational.

Are you Dipping or Wicking?

Oil-filled cutters are a relatively recent invention and are very popular. They have a little wick inside to slowly “feed” the cutting wheel with lubricant.

Oil-filled cutters can be contrasted with their predecessors which were not oil-filled. Many of these “more primitive” cutters are still bought and used because they tend to be cheaper than oil-filled cutters. With these older glass cutters the method of lubricating the cutting wheel is called “dipping” and it means you dip your glass cutter’s cutting head into a jar containing your chosen lubricant, perhaps with some rag or wadding at the bottom of the jar. Many people who are “dippers” seem to be “traditionalists” and use kerosene.

Generally speaking I tend to use an oil-filled glass cutter containing “cutting oil” but there are occasions when I find myself with a more traditional glass cutter closer to hand. Rather than dipping a traditional cutter into a jar I use a shallow tin (with a hinged lid) that contains a few layers of old denim rags heavily soaked in cutting oil. I replace the rags from time to time as glass particles accumulate. Having a shallow tin with a hinged lid is handy because it does not leak when transported “off site”.

Although it may not yet be apparent, there are justifiable reasons to use one kind of lubricant in an oil-filled cutter but a different kind when dipping. For example, some people suggest that “cutter oil” is much too viscous to wick properly in an oil-filled glass cutter and suggest that it  is therefore only suitable for dipping.

Good Cutter Lubricant Characteristics

Here is my candidate list of characteristics that may be important when comparing one “cutter oil” or other lubricant with another. The relative priority of these characteristics will depend on personal preferences as well as technical considerations – for which words like “appropriate” are deliberately vague. You might choose to make your own list and ignore mine.

  • Remains liquid at room temperatures (and relates to appropriate viscosity);
  • Will not thicken or chemically degrade over time (eg “oxidative stability”);
  • Ability to biodegrade and “save the planet”;
  • Will not corrode the metal parts of a glass cutter;
  • Appropriate evaporation rate (which can also relate to noxious vapours);
  • Residues evaporate or burn away cleanly (for fused glass work); and
  • Residues are easily washed or wiped away (for copper foiled work).

You will find some alternative perspectives within the online discussion here.

An appropriate viscosity depends on how you are using your “cutter oil” and at least to some extent is a matter of personal preference. It also depends on the “leakiness” of the cutter head. And there are several commentators thay say that we must ensure our oil-filled cutter can effectively “wick” the oil and that it must be less viscous that we might use when dipping a glass cutter. This distinction here would be paraffin vs. kerosene, or a mixture of them both.

Lubricants that chemically degrade will have a limited shelf-life so stability is important. One mechanism by which some oils degrade is by slowly oxidising and in the case of vegetable oils this can be spotted both in terms of the increased viscosity and also the rancid smell. So, if a lubricant is susceptible to oxidation then the process causes the lubricant to progressively thicken and it will ultimately reach a point where it will “gum up”. This will be a problem for oil-filled glass cutters and remediation of the “mess” is going to be more difficult.

The ability to bio-degrade and other environmental concerns should be balanced against a recognition that we will do not use large quantities of which ever lubricant we choose. In the broader context of “environmental concern” we should also recognise the far larger environmental damage caused by putting whatever lubricant we might choose to use (even the “environmentally friendly” ones) into a plastic bottle, packing and shipping it around the world and let’s not forget the final step of the environmental damage caused by us just “popping out” in our car to buy the darned stuff!

Some choices for “cutting oil” are smelly and can evaporate quite quickly. Working in a confined space can be a problem with any volatile substance. Bear in mind that vapours causing headaches are not always the most serious concern with a volatile liquid product so do remember to ask your supplier for the Manufacturer’s Safety Data Sheet (MSDS) or hunt them down on the Internet. If you are an employer then asking for MSDS information for all your chemical products should be part of your Health & Safety management routine.

Some people eschew the use of cutting oil and all other lubricants, choosing to score glass with a dry cutting wheel. Sometimes there may be a rational basis for the decision though many point out that the life of a cutting wheel and the quality of a score can affected detrimentally – something that I will consider and question later.

With a list of desirable lubricant properties and examples of what people are using it’s time to give some rational thought to asking why the scoring process might need some kind of lubricant. We will first look at the scoring and healing processes within glass for one perspective and then look at the relative hardness of cutter wheels and glass as another perspective.

Scoring and Healing

Many people, like myself, subjectively believe that “old scores” seem to be harder to break than a fresh score and the commonly held belief is that there is a “healing” process that takes place very slowly within the glass. But, as is usual within stained glass crafts, it is always possible to find someone with an unevidenced and unjustifiable polar opposite opinion such as this one: “Glass doesn’t heal. That’s a myth.

Is it perhaps the conflicting and sometimes irrational hearsay, magic and mysticism that I encounter in stained glass crafts that causes me to do these blog postings? Hmm. Probably.

To complicate matters further, I see that many people believe that using a lubricating oil when scoring results in a better break – yet some believe a dry score is better. More mysticism, magic and hearsay to deal with.

Let’s see if some science and rational thought can help us find meaningful answers. We need a plausible explanation for why glass scored with a lubricant might be improved. It should also explain why “old scores” might be harder to break. With such information we are in a better position to choose the best “cutter oil” for our glass cutters and dismiss some more of the myths, magic and hearsay you’ll encounter on the Internet.

My curiosity was aroused by a visit to this strange article about glass cutting where a claim is made that alkaline substances that contain hydroxyl ions, such as spit, will help with glass scoring. An interesting idea but suspicious because I know that spit can be acidic (after eating) as well as alkaline (after tooth brushing). Also, the oft-mentioned assertion that “Glass is a super cooled liquid” in this source causes me to be extra suspicious because although the atomic structure of glass resembled what can be observed in any supercooled liquid phase, glass displays all the mechanical properties of a solid. OK, I see you yawning… Put simply, glass is an amorphous crystalline solid, not a liquid. More about this at Wikipedia in case you’re interested.

But I then found a more reliable source via this page which contains a link to a YouTube video which in turn cites a Spectrum Glass article that cites the Scientific American journal as a source. I was unable to find the original Scientific American source but did at least find the Spectrum Glass source.

The Spectrum Glass article tells us that “water causes glass to crack more easily because when a water molecule enters the crack, a reaction occurs in which a silicon-oxygen bond at the crack and an oxygen-hydrogen bond in the water are cleaved, creating two hydroxyl groups attached to silicon. As a result, the length of the crack grows by the size of one bond rupture. The water reaction reduces the energy necessary to break the silicon-oxygen bonds, thus the crack grows faster.

So, it is the ability to produce hydroxyl ions, rather than being an alkaline substance, that explains how bonds are “helped” to cleave by the use of water. And I note that spit contains water. This all seems to be plausible but I can’t find any explicit information relating to the “healing” process or the use of oil so I’ll have to some inferring and this means I might be wrong. You can decide for yourself…

My first thought is that mineral oils might also assist with the same crack-forming process but with a subtle difference because mineral oils contain no water and therefore can not produce hydroxyl groups. This leads me to suggest that what’s most important is that oil gets into a glass rupture in exactly the same way that water does. But, unlike the water situation, the physical presence of the oil rather than a chemical change is the barrier to the re-establishment of silicon-oxygen bonds that have just been ruptured. We therefore have a plausible mechanism that I hope correctly explains why oils will also assist with the crack-forming and maintenance process. This is alluded to by at least one commentator on the Internet so may indeed be correct.

My next thought is that is reasonable to assume that any water within the score line fracture will eventually escape and evaporate away, leaving a “dried out” crack. It is also reasonable to assume that the same thing will happen with mineral oils and other liquids, though not necessarily at the same rate as might happen with water. My suggestion is that the silicon-oxygen bonds in a dried-out crack will be able to re-form and “heal” the crack at least to some degree, albeit slowly. We therefore have a plausible mechanism that I hope correctly explains the long-term “healing” effect.

In conclusion, we now have rational explanations for why a fluid can help the crack-forming process and for the “healing” effect. We therefore have a rational justification to use a water-based or oil-based cutting fluid rather than to use dry scoring as a normal practise.

Thinking About Hardness

Many people, like myself, subjectively believe that cutting oils (or whatever) will lengthen the life of a glass cutter’s wheel. Glass is hard and metals are soft.  It all seems so obvious.

But once again, heresay, magic and mysticism rules, rather than rational thought and science. We need to look closer and think harder.

To understand whether or not a glass cutter’s wheel gets “ground down” by fragments of glass requires some understanding of how “hard” the materials are, for which there are many “scales” of measurement. Perhaps the best-known and popular measure is the Mohs scale of hardness. You can visit here and here for more information about the Mohs scale and hardness.

The Mohs scale has smaller numbers for softer materials and larger numbers for harder materials. This means a harder material can “scratch” something of equal or lower hardness.

Here are some hardness measures on the Mohs scale:

  • 4.0 to 4.5       steel (cheap wheel cutters)
  • 5.5 to 6.5       glass (soda glass tends to be quite soft)
  • 9                      tungsten carbide (posh wheel cutters)
  • 9                      sapphire (cheaper very old-fashioned cutters)
  • 10                    diamond  (posh very old-fashioned cutters)

So, for example, a diamond will easily scratch any kind of glass. This much is common knowledge.

More important to us is a confirmation that glass will scratch and abrade a steel cutting wheel. But I hope you can also see that glass will not scratch or abrade a tungsten carbide cutting wheel.

So, these discoveries mean that the life-lengthening effect of using a cutting oil definitely holds true for steel cutting wheels but does not appear to be true for tungsten carbide cutting wheels. If there is any rational reason to use a cutting oil with a tungsten carbide cutting wheel then it’s not related to the hardness of glass. This brings into question the commonly-held view that cutting oil lengthens the life of our (tungsten carbide) cutting wheels.

To end this section I leave you with a tricky question, or perhaps I should say a trick question… If steel is softer than glass then how does a steel cutting wheel manage to produce a usable score line in glass?

Reasons to Lubricate, Or Not

If you’re still reading and haven’t yet fallen asleep with boredom, you’ll begin to understand that comments such as “oil helps you see where you have scored” and also “with light pressure, no oil is needed” are of limited value and need clarifying and justifying before acceptance.

So, I think we are now in a position to make two lists with which decide whether or not to use a lubricant with our glass cutters. Here are my suggestions but you might make different lists:

Reasons to lubricate:

  1. Lubricating the cutting wheel keeps it spinning freely and smoothly.
  2. Free up any shards of glass that could get stuck in the cutting head assembly.
  3. May help to preserves the cutting wheel edge (if stainless steel) by washing away glass particles.
  4. Prevents shards of glass from flying around.
  5. Keeps the scored line open and slows down the “healing” process.
  6. Heat generated by the scoring process is dissipated.
  7. A trail of lubricant helps to make feint score lines more visible

Reasons not to lubricate

  1. Tungsten carbide cutting wheels are harder than glass
  2. Lubricants make a mess that needs to be cleaned away before copper foiling or kiln firing.

I can’t make the choice for you but my inclination is to use a lubricant, especially when using a steel wheel,  but not worry so much if I’m using a tungsten carbide wheel.

Choosing What and Why

Now that we’ve done some “hard thinking” and decided whether or not to lubricate we’re in a position to make sense of the choices available to us.

Dry Cutting has an advantage when copper foiling because the copper foil’s adhesive will better adhere to glass if there is no oily deposit. The alternative is to wash or scrupulously wipe the glass pieces.

Whether or not dry cutting is an advantage for kiln firing glass is questionable. I say this there’s lots of opinion, and I suspect a lot of irrational paranoia, but little basis in testable facts on issues relating to contaminants (even fingerprints) causing devitrification. Here are a couple of comments to consider and contrast… A clean cutting oil is a simple hydrocarbon mixture which will cleanly evaporate or”burn off” within a kiln – but we are told this can cause devitrification. However the use of other “contaminants” such as Glastac or White Glue (PVA) are routinely used and also “burn off” – but we are told these are not a risk for devitrification. This all looks rather self-inconsistent to me. We want facts not superstition and hearsay!

Dry cutting with steel wheeled glass cutters is a bad idea because glass particles are harder than steel. However, tungsten carbide wheels are harder than glass so dry cutting ought to be OK with these cutters.

Vegetable oils are very cheap and abundant, they have a low odour, evaporate slowly and are biodegradable so they have good environmental credentials. However, they have a rather high viscosity that increases as the oil slowly oxidises and turns rancid, causing a cutter to get “gummed up”. A conclusion for vegetable oils is that they should only be used in an emergency, but if you really are in this situation then would be perhaps be better to siphon-off a little petrol or diesel from a car instead if you can cope with the odour?

Mineral oils based on kerosene, paraffin and mixtures of them are our current favourites. They are also the basis for commercial products. Kerosene is lighter but more volatile and more likely to cause a lingering odour and cause headaches but some believe paraffin is a little to viscous. Either way they are being used in small quantities so perhaps the environmental problem of them not being biodegradable is not such a major consideration.

More to the point, if you want to “save the planet” you should also be concerned when buying an “environmentally friendly” alternative. Do we not do more environmental damage by putting it into a plastic bottle, shipping it and then going to SGC supplier in the car to buy it?

The prospect for using water or a modern water-based “environmentally friendly” formulation is worth considering because they can be wiped away or washed off and leave no residue. It is certainly a reason to consider them for copper-foiled work and for kiln work but the reservations I have for dry cutting should also apply here as well. Another concern is whether water and water-based formulations might slowly corrode or oxidise the wheel and spindle of a glass cutter. I can not tell you if this happens because I’ve not use these formulations.

Make Your Own Formulation

Formulating your own “cutting oil” based on mineral oils is easy but to produce your own “environmentally friendly” is another matter.

From what you’ve read you’ll realise that “mineral oils” come in many disguises, such as sewing machine oil, baby oil, kerosene and paraffin. They’re all the same but slightly different. This means you easily formulate your own cutting oils by mixing them to get the right odour, viscosity and so forth.

I have inherited enough “cutting oil” to last a lifetime so I’m unlikely to experiment in this area. Sorry. This time you can lead and I’ll follow!

Over and Out

I hope you found this useful even though I got truly distracted from my original intention to write about glass cutters!

Posted in Cutter Oil, Cutting Oil, Glass Cutter, Lubricant | Tagged , , , , , , | 10 Comments

Stretch, Bend and Squiggle

If you only ever use stringers for straight lines and think that the advent of 0.5 mm diameter stringers is exciting then this blog probably isn’t for you.

Ditch those straight line stringers. Get stretching, bending and squiggling. Read on!

Stretch and Bend

Perhaps the quickest and easiest was to break out of the confines of straight line stringers is to use a perfectly ordinary wax candle flame to perform some very simple tricks that can sometimes be remarkably effective. Some experiments you might like try are to:

  • Soften the middle of a stringer then pull the two halves apart. You will either get a very thin length of stringer or two pieces with tapering ends;
  • Soften the middle of a stringer and then either manually bend or allow gravity to bend the stringer. You can repeat this to make complicated shapes;
  • Melt the ends of the stringers so that they are fat and blobby. Not so exciting but can also be done.
  • Try a combination of effects for added fun and excitement!

DSCF1868 Squiggle TileOn the right you can see a very simple example of a square glass base onto which a few bent stringers have been laid. As you can plainly see, this particular example was done to a full fuse and the result is rather abstract. The joy and excitement comes from waiting to see exactly how they sag and then fuse into the base layer.

There is however a problem with using a wax candle in that the flame produces a sooty deposit on the stringers. A lesser problem is that a candle flame is not very hot.

A damp cloth, a dry paper hankie and a piece of toilet tissue are all able to clean off the carbon deposit from bent stringers.

The soot problem can be significantly reduced and the flame temperature can be increased by investing in spirit burner. Spirit burners use alcohol, or more specifically methylated spirits, to produce a hotter and cleaner flame. An additional advantage is that they are not so brutally hot as a Bunsen burner or a bead-maker’s torch.

DSCF1964 Spirit Burner

If you are not familiar with spirit burners then a picture or two might help you understand what’s involved. The sharp-eyed amongst you with an elephantine memory may recall the old Victorian spirit burner I was using in this blog. If you didn’t, here’s a picture of it…

As you will see it performs exactly the same job as the modern version you will see here or this fancy stainless steel version.

Spirit burners are not so commonplace as they were in the “olden days” but new ones can still be purchased from a good scientific equipment suppliers (as I’ve just shown you). You can also find them in old chemistry sets and, if you’re really lucky, you may find a lovely glass spirit burner like mine in an antique dealer’s shop. Sometimes you will find spirit burners being used in primary schools where there’s a teacher who isn’t afraid of science. Wimpy teachers use tea lights.

I believe there are also camping stoves that are spirit burners but I have never seen or tried one. I suspect they will not be suitable.

Over at YouTube you will find a video where someone has made their own spirit burner. There is also an Instructable here which is very similar. Curiously, neither thought to make use of a piece of string (or even a proper wick) rather than a paper towel. I have also seen examples where jam-jars are used with string as a wick. Make your own if you’re adventurous!

So, that’s the stretching and bending and spirit burners dealt with.

Next we head off into the realms of clay, plaster of Paris and squiggles.

Let’s Squiggle

I’m not exactly sure what made me think of using a mould to make squiggly stringers but suspect it must have been the Rod Pod moulds, such as this one, that stuck in my mind.

DSCF2792 Initial SquigglesMy first experiments were to make small stringer squiggles using moulds made from plaster of Paris and clay. To begin with I had no idea about how far apart the teeth of the moulds should be, nor the depth of the channels, their shape profile, nor whether plaster of Paris or clay would be the better material to use. On the right you can see my first moulds and the some of the results of my first firing.

I found the plaster of Paris moulds were easy to create but fragile. What I liked the most about the plaster of Paris is that they could be re-shaped and re-used to explore different shapes and profile with nothing more than abrasive files and sandpaper. The plaster of Paris I was using was sold as “economy casting plaster”. I did, of course, wait until these moulds were properly dry before using them.

The little clay mould you can see at the right of the picture was made with the cheapest clay I could find – sold as being modelling clay that is apparently unsuitable for being kiln fired. To be perfectly frank, had I known how cheap and nasty this clay was going to be I would have dug up some better clay from my own garden!

For my first foray into working with clay since primary school I also bought the cheapest and nastiest set of clay loops on handles that I could find on eBay. Although these tools were very useful for getting the approximate shape of the teeth and grooves, I found wet fingers, pencils and other random household implements to also be very useful. Fingers are such fantastic and adaptable tools, don’t you think?

I did wait until the clay had dried-out before using the clay mould but I did not pre-fire it before using it in my glass kiln. Knowing that at least some chemical changes would occur in the clay during firing I removed the bung from the kiln so that water vapours and whatever else might be released could escape.

Despite only being fired to a moderate slumping temperature the clay became much harder and stronger but more brittle. No longer would water make it soften and “melt away”. It may not be as tough and waterproof as a fully-fired piece of clay (at temperatures a glass kiln can not reach) but it has proved itself to be perfectly adequate for the purpose for which it was intended – to make stringer squiggles.

In case you’re want to know what kiln schedule I used for this (and subsequent) experiments then all I need to say is that you should choose a familiar kiln schedule of the kind that you would use to slump a bowl or a bottle. So, that’s more than a tack fuse but not very hot and with relatively slow temperature ramps. You will know if you’ve got it right because too hot causes the squiggles to break up into small pieces. Too cool and nothing will happen. Too quick and the moulds may crack from thermal shock. Too slow and you’re wasting electricity.

On the subject of thermal shock, I should note that I would not recommend trying to make squiggles in a microwave kiln. My experience is that moulds crack under the fierce heat and rapidly changing temperatures within a microwave kiln. This fierce heat is also more likely to convert your stringers into little blobs of glass in the gaps between the teeth of the moulds.

Oh, and I didn’t use any release agents on the moulds. No thin fire paper, no kiln wash, nothing. These are experiments for some other day.

Squiggle Some More

The first experiments led me towards an understanding of suitable kiln schedules, dimensions of moulds that worked and an appreciation of problems that tend to occur. From this I made a bigger and improved “version 2” mould from clay.

Although my initial experiments suggested a particular distance between successive teeth for the “version 2” mould, it should be borne in mind that there’s no reason why you can not lay your stringers diagonally to achieve a longer distance between the teeth.  Ah, the wonders of geometry.

DSCF2798 Second SquigglesThe picture on the right shows you only a portion of a bigger “version 2” clay mould. This mould is half the length of a stringer. Well, it was until I accidentally trod on it and snapped a lump off one end!

Notice that I have used the edge of a ruler to make little notches on the mould’s teeth. I’ll come back to why in a minute.

What you can’t see from this picture is that this mould is double-sided. The side you can see has a slightly larger distance between the teeth. Secondary advantages for making this mould double-sided is that the thermal mass is smaller and that air can move beneath the mould. Therefore, in theory at least, this mould should warm up and cool down more quickly and therefore cope with a slightly quicker kiln schedule.

Not revealed by the picture is that stringers have a nasty habit of rolling, even if you have a nicely levelled kiln. Not only does this rolling happen while you are trying to load the kiln, causing much frustration, but it also happens when the lid of the kiln is down, you can’t see what’s happening and everything’s too hot to handle anyway. This is why I used the ruler to make those little notches – they try to stop stringers from rolling!

So, in practical terms, what this all means is that you can expect pairs of stringers to roll against each other whilst remaining on top of the mould, giving you two-tone squiggles. At worst one or two will roll off the mould and attach themselves to other work inside the kiln or even the kiln itself.

If you look carefully at the last picture (click and it will open-up bigger in another window) you can see the 2mm stringers are more squiggly than the thinner 1mm stringers. It is the weight of the thinner 1mm stringers that is the problem – not heavy enough to sag as much as the 2mm stringers. The distance between the teeth of the mould does not resolve this difference in behaviour but ought to have some effect. If you can remember your High School physics relating to forces and moments then you should have a clue about why a fatter stringer will sag more.

Notice also that the shape of the squiggles is asymmetric – but this problem disappears when you use them.

Although not show here, the version 2 clay mould was subsequently attacked with sandpaper to make the teeth more rounded to achieve a “softer” profile in an attempt to reduce two problems that were encountered:

  • If the firing temperature is too high then the glass sags into the troughs and as it does so the curves of glass “grasp” the corners of the teeth of the mould. The consequence is that little pieces of clay debris attach to the glass. This is a predictable behaviour of glass but can you think why it is worse at higher temperatures? Hint: the answer relates to viscosity and the degree of “shape conformation” that results from the hotter kiln schedule.
  • If the firing temperature is relatively high then the stringers sag more deeply into the troughs. This becomes a problem when cooling down because the stringers (especially the 1mm stringers) tend to break into shorter lengths. Again, a predictable behaviour. But what is the cause? Hint: the answer relates to expansion coefficients and lack of a “slippy” release agent on the mould.

I have not solved the breakage problem by changing the profile of the teeth but working at a lower temperature does have positive benefits in this regard.

Nor have I solved the problem of little pieces of clay attaching to the glass when processed at a higher temperature. As the processing temperature is raised, so the problem increases. Again the problem can be resolved, at least to some degree, by processing at a lower temperature. Like other glass workers I find that kiln-related “attachments” (including clay from these moulds) can be removed as follows…

When clay, kiln materials or any “rocky gunge” gets attached to glass during firing then the problem can be dealt with by acid treatment. Here we are relying on an acid to react with the “gunge” in such a way that it either all dissolves away or enough of at least one component part of it is dissolved away sufficiently to make the remainder easier to remove by other methods.

You can liken this acid treatment to leaving an egg in vinegar for a long time. As time passes it gets increasingly easy to crack the egg shell because the shell is being dissolved away. Remember that egg shells are made of calcium carbonate, just like limestone – this analogy isn’t so daft!

Unsurprisingly, the acid of popular choice to deal with this “rocky gunge” problem is ordinary vinegar.  The vinegar (ethanoic acid) we eat with our fish and chips is a rather weak and dilute acid so it takes several hours to work its magic on “rocky gunge”. You can also use stronger acids such as hydrochloric acid, sulphuric acid or nitric acid but do take precautions to ensure you’re not using them at an excessively strong concentration. I tend to use hydrochloric acid at a concentration between 1M to 2M. Do you remember your High School chemistry relating to “molarity”? And the subtle difference in meaning between a concentrated acid and strong acid?

So, after a few hours “soaking” in acid some of the “attachments” will be dissolved by the acid. What remains will either be larger pieces that have yet to be completely dissolved or are a different kind of “rocky gunge” that will not dissolve. Nevertheless, the structure of whatever remains will be weakened enough such that it can be removed much more easily with a fine needle-pointed picking tool (like dentists use) or even a finger nail.

Squiggles In Use

As usual I don’t give you some fantastic piece of artwork to demonstrate what can be done with whatever it is I’m chattering about. This time you get a heart and two fishes as trivial demonstrations of what the squiggles look like when used.

DSCF2809 Fish and Heart UnstrungIf you look closely at the detailed shape of the freshly-made (in the previous picture) you will notice that the curves are not even and it is most noticeable where the stringers were sat on top of the clay teeth. You will now see from this picture (on the right) that a subsequent firing onto a glass base deals with these minor “defects” and the result is a much softer curving. Click the image and it will open in a different window so that you can look in more detail.

Is one of the fish an electric eel and the other a rainbow trout? Perhaps not.

Some Conclusions

These are, I think, the important conclusions from my experiments so far.

  • A candle or spirit burner can be used to stretch and deform stringers very easily.
  • Making your own mould is a lot cheaper and a lot more fun than buying one.
  • Plaster of Paris is great for initial experiments but clay is better for your “production” moulds.
  • Do not be concerned by the quality of the clay you are using, nor the quality of tools available to you, nor indeed the finer points of construction of the mould. You are not making a decorative item to sell – you are making a tool.
  • Fine notches on top of the teeth of the mould will help to stop stringers rolling around.
  • Put your least valuable other kiln work adjacent to the squiggle moulds so that stringers rolling off the mould will only cause minor inconvenience and much less annoyance.
  • 2mm stringers work the best because they have enough weight to sag nicely into the voids between the teeth of the mould. The problem with 1mm stringers is that they are too light to sag significantly, even when the spacing between the teeth is quite long.
  • If the processing temperature (or duration of processing) is insufficient then the degree of sagging will be small.
  • There is a limited range of processing temperatures (or durations for processing) within which the stringers squiggle nicely without causing breakage or clay-attachment problems when they cool down.
  • If stringer squiggles break or are heavily contaminated by clay “attachments” then the processing temperature (or processing duration) is too high.
  • If the temperature (or processing duration) is massively too high then the stringers will flow downwards into the voids and may become fat blobs with little or nothing connecting them.
  • Treatment in vinegar or other dilute acids for a few hours will “soften” or remove clay attachments from stringer squiggles. Pointed tools (as used by dentists) can be used to remove stubborn attachments, as can finger nails.
  • And finally, I wouldn’t recommend putting these moulds and stringers into a microwave kiln. My experience is that microwave kilns heat up far too dramatically causing moulds to crack and the amount of “processing” for the glass is far too difficult to control.

That’s all. I now leave you to have a fun time with clay then make your stringers twist and squiggle.

April 2017 Update

Here are a few extra thoughts and comments relating to the creation of a larger squiggle mould.

My latest squiggle mould is longer. It is exactly half the length of a stringer which means I no longer accumulate short lengths of stringer – less waste is good!

Getting a large flat lump of clay to dry out without curling at the edges was a nightmare until I learned to slow the process down. Half of the nightmare was because I did not know much about how clay behaves as it dries. The other half of the nightmare was having to guess what to do when things were not progressing well.

To begin with I used a cool damp garage in winter and covered the mould with a layer of wood with a modest weight on top to provide a gently “flattening pressure”.  I used some newspaper between the wood and the clay to help “wick” the water out of the clay. Occasionally I would flip the mould over. This worked well for awhile, but not well enough…

Towards the end of the clay drying process the edges get drier than the interior. This differential drying causes the edges to contract more than the interior which in turn forces the middle of the mould to bow upwards or downwards. The wood and weight did not stop this happening. I think the reason behind this can be explained by science: evaporation of water from the edges will eventually be faster than water can be drawn from the interior, causing a “dampness gradient” which in turn causes a “shrinkage gradient”. If you’re a keen gardener (or a soil scientist) you will know that clay is notable for its ability to hold onto water, particularly in drought conditions. In severe droughts clay soils shrink until they “break” into what looks like crazy paving.

There are two ways to resolve the shrinkage problem, each having its own time and place in the drying process.

The way to increase the drying rate in the interior of the mould is to remove the wood and the weight. The aim is to get the interior to dry (and shrink) as fast as is happening at the edges. This trick helps but does not always stop the curling from happening.

When curling happens, the effect can be reversed by judicious use of a fine water spray around the bowing edges to help soften (and therefore expand) the clay around the edges.

Repeating those last two activities until the clay dries out evenly will leave you with a large “flattish” area of clay ready for firing.  The last thing you want is a wobbly mould that allows stringers to roll about so you will then need to use some fine sandpaper to  “improve” the flatness of the base and get the ridges all at the same level. Remember to “fix” the profile of the ridges and add those anti-roll cuts.

I have found that the depth of the channels is not as important as the profile of the ridges. A good strong curvature of the ridges will eliminate clay capture by the squiggled stringers when fired. I have also been using kiln wash on my moulds and this also seems to help.

I have not found any advantage from using Bullseye Thinfire paper between the stringers and the mould.

I have learned to wipe the squiggled stringers with a damp cloth rather than clean them in a bowl of water. I break fewer of them by wiping them than washing them.

To get consistent amounts of squiggle I have learned not to mix 1mm with 2mm stringers. This is because 1mm stringers need much more heat to bend as much as 2mm stringer (as was noted in the original blog).

And best of all is that I now have a variety of squiggle moulds, each with different distances between the ridges and troughs. To be scientific (or maybe mathematical) this means I can now choose the frequency of squiggling to suit a particular design.

Posted in Experiment, Microwave kiln, Money-saving ideas, Mould, Stringer | Tagged , , , , , , | 4 Comments

Buzz Those Frits

For some time I’ve been using my fingers to sprinkle or place frits. I have also been tapping them out of a simple home-made frit dispenser. All very simple and low-tech but not very precise and rather laborious. So I have been looking into alternative methods and you’ll maybe recall how I have described the use of CMC to squirt your fits elsewhere in my blog.

A Simple Frit Dispenser

A long time ago I stopped using folded-up pieces of paper to dispense frits. Instead I now make simple little home-made frit dispensers. They work remarkably well considering they are nothing more than pieces of cardboard stuck together with pieces of sticky tape. If you want to make your own, look at the example cutting plan.

Frit TroughAll you need to do is cut around the outline, fold the sides upwards and glue (or otherwise attach) the tabs marked T to the back. You should end up with an open-ended trough with a relatively narrow opening slot. They take just a few minutes to make and you can vary the size of the opening slot to suit the task at hand.

As much as these little tools have been remarkably useful, endlessly tapping their sides to dispense frits can get rather repetitive and boring. So, I decided to look at alternatives that are commercially available.

Enamel and Glass Sifters

There are a number of tools where vibrations caused by a spring being pushed back and forth against a screw thread cause frits to be dispensed by vibration. Some tools dispense frits through a sieve mesh whereas other dispense through a small hole. A quick trip to in the USA illustrates a few examples of what I’m talking about. I like their design simplicity, particularly the use of a spring juddering over a screw thread to cause vibrations. But they are manually operated and each one costs significant money but does only one task.

Some Household Alternatives

You may also be familiar with hand-held tools that are used in the kitchen. You have probably used some of them for your glass work.

The sifting alternative to my little cardboard gadget would be a plain ordinary open-topped tea strainer. But have you considered the enclosed tea strainers (also used to infuse spices and herbs) with a refillable ball-shaped mesh at the end of a handle? A simple as these are, they are useful for spreading frits over a wide area in a reasonably controlled manner. Their main disadvantage is a fixed mesh size.

Icing sugar shakers are another alternative (also used to dust chocolate or cocoa powder). They are nothing more than a small cylindrical container with a meshed lid. These can also be useful sometimes but are only useful for distributing frits over a wide area. They too have a fixed mesh size but it is possible to remove the mesh from some, allowing a differently sized mesh to be used instead.

What other household tools do you use when working with frits? Do please tell us all!

The Powder Vibe

The Powder Vibe from Bearfoot Art is an interesting tool. It originally used a Hummingbird flosser from Oral-B to dispense frits. Apparently the flosser is no longer available but a newer design has been produced. You will find more information in videos here and here, both of which which suggest this might be a rather useful tool but the power unit costs around $42 and the tips cost around $8 to $10.

I am particularly impressed by the creative use of nested metal tubes in the new version (and indeed the use of a flosser in the previous versino). I am also impressed that nested tubes are also used to allow either one or two AAA batteries to be used (thereby catering for low and high power setting).

What caught my attention was the use of electrically-powered mechanical vibration. I have a couple of tiny inexpensive toys that use vibration motors. I also happen to have some tiny little vibration motors. Time to start experimenting. Time to make a prototype frit buzzer!

The Frit Buzzer

What I will now describe for your delight is a simple electrically-powered tool that uses my simple cardboard frit dispenser as a starting point. It will not take you much time to construct something similar, it will not cost a lot of money, and you will find it works rather well.

Photo-0003 Frit Squiggles 2In case you need some convincing, here are some squiggles, lines and heaps of black powder frit to show you what can be done without any skill or experience with nothing more than my first rudimentary prototype.

And when I say without skill or experience, I really mean it! What you see was my first attempt with my first prototype. I am sure that with a more suitably shaped frit dispensing trough and a little practise I might be able to so much better. Don’t be deterred – read on!


Here you see two views of what I made. You will need to construct something similar. Click on the pictures to study larger versions in a new window.

DSCF2577 Top

DSCF2575 Underside

On the top of the tool you can see the simple cardboard frit dispensing trough that I described early in this posting. It has a rather wide opening so produces rather large heaps and rather fat lines. I will be removing this trough and replacing it with a trough that has a narrower exit.

You will also see that the cardboard dispensing trough is glued onto a wide flat lollipop stick. Underneath the lollipop stick are a vibration motor, a pushbutton switch and some batteries connected together with wires into a circuit. I used some Uhu/Bostik glue because it is weak and easy to remove – adequate for a first prototype!

One point of note relating to the vibrating motor I used is that the eccentric weight protrudes beyond the end of the lollipop stick – for this particular motor the eccentric weight is wider than the diameter of the motor so could not be mounted entirely underneath the lollipop stick.

Another point of note is that I am right-handed so the pushbutton faces towards the right. You may not be right-handed!

VibratorCircuitWhen the component parts are glued together you will be ready to connect them electrically so a circuit diagram for what you are trying to achieve is on the right.


The Electrical Components

The vibration motor is not something you’re likely have readily available. If you have a broken child’s toy that used to vibrate then you’re likely to find a vibration motor inside it – re-use it! I bought my vibration motors in a 5-pack through eBay, intending to make silly things with my nephew. They cost a few tens of pence each.

DSCF2574 MotorWithin sensible limits, it does not matter how big or small the vibration motor is. The main thing you are looking for is a motor which has an eccentric weight on the end of the shaft. It is this offset weight that causes the vibrations in childrens’ toys, adult “toys”, the Powder Vibe and my own prototype.

The size and weight of the motor has more of an effect on how comfortable your frit dispensing tool will be when used. What my prototype tells me that even a tiny vibration motor is sufficient– the motor itself is just 10mm by 5mm. On the right is a close-up picture of the vibration motor I used. Notice the eccentric “lump” of metal on the end of the motor shaft.

The number and size of batteries you will need depends entirely on the motor rating. The motor I used has the ratings 0.11A at 1.5V and 0.23A at 3.0V. When used with rechargeable batteries I found the motor consumed 0.18A at 2.8V. What is important is that the specification says it will work at 1.5V and 3.0V, which means I could use either one or two AAA batteries. I could have chosen larger AA batteries but I decided that they would make the prototype tool rather heavy and bulky, even though their larger capacity would make them last longer before needing replacement.

In order to fit and replace batteries it is sensible to put them into a battery holder. Here is where you will need to decide on a one-cell or a two-cell battery box. I chose a two-celled AAA battery box because I happened to have one in my spares box. Two batteries (3V) are OK for my motor so means more powerful vibrations than using just one battery (1.5V).

The switch I used is known as a single-pole momentary switch because it has one set of connections and is only “on” for as long as the button is pressed. A double-pole pushbutton switch is equally good but will cost a few pennies more. Do not get a “latching” switch because you will have to press to turn it on and press again to turn it off. Using a toggle or slider switch is also possible but will not be as convenient as a pushbutton switch.

From the circuit diagram (above) you will realise that there are three components to be connected into a simple circuit. If you can’t solder wires together, find a friend who can.

And  a word or warning: It is all too easy to melt the plastic battery holder even with my 15W soldering iron so don’t try soldering the circuit with your 100W stained glass crafts soldering iron.

Obvious Improvements

I have already realised that I should try a new cardboard frit dispensing trough with a narrower exit. Another possibility is to make one from corrugated cardboard so that parallel dots and lines can be made quickly and easily. This idea could be refined and made more flexible with front-end attachments to a standard open-ended trough.

For precise control it is important to dispense the frits close to the place where they are required so the prototype will need altering so that the dispenser exit does not have lots of “lumpy things” underneath that get in the way. Moving the switch and the motor backwards are obvious starting points, as is choosing a smaller pushbutton switch. And I wonder how it will work with the motor attached to the back of the battery box.


I am sure my first prototype will not last long before it falls apart. This is not a problem because it has been built with an expectation that it will be messed about with and modified to explore possibilities. If nothing else, the prototype tells me that a tiny little vibration motor, a pushbutton switch and two AAA batteries in a holder are all that’s needed. It also confirms in my mind that the Powder Vibe might indeed be a really useful tool.

I now invite you to make and explore your own prototype. Use it to decide whether you want to continue developing your own design. Or will it cause you buy a Powder Vibe?

And if you have any good ideas, please let me know!

Posted in Experiment, Frit, Frit Sifting, Money-saving ideas | Tagged , , , , , , | 4 Comments