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 , , | 3 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 , , , , , | Leave a comment

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 , , , , , , | 8 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

Which Solder Should I Use?

There are several kinds of solder available for stained glass work. Are you always using the right kind?

There’s a lot of good advice and information on the Internet. There’s also a lot that isn’t. That’s the trouble with the Internet. So, for this posting, I decided it was time to do some reach useful conclusions about why there are different grades of tin-lead solder, how they perform and reach conclusions about how they are best used.

So, let me guide you by explaining and contrasting what I have learned and experienced with the tin-lead solders we routinely use. But I will not talk about lead-free solders because I never use them.

It’s time to learn and make use of some materials science…

Solder Properties and Behaviours

There are several grades of tin-lead solder available to us, with tin concentrations between 5% and 70% by weight in their alloy mixture. In reality we only tend to use a few of the various grades – the ones that are useful for our craft.

Incidentally, I’ve seen solder described as a compound. This is wrong because an alloy is a mixture, not a compound. Mixtures are when two or more things are brought together but are not chemically bonded together. Compounds are when two substances chemically react to form a third substance. But, as usual I digress.

The important thing to understand is that different grades of solder will behave differently because they are different mixtures and this in turn means they will have different physical characteristics (such as melting point or electrical conductivity). We need to understand how some of the differences might affect our craft work and in turn guide us towards rationally choosing the grade of solder we use for a particular task.

One property of the tin-lead alloys is that the greater the tin proportion, the greater the solder’s tensile and shear strengths. What this means in practical terms is that higher tin proportions result in a “harder and stronger” solder. But tensile strength and shear strengths are not the most important issue for the stained glass worker, though they do have a subtle effect on the structural strength of what is constructed.

Of greater importance to the stained glass worker is how solders perform during the act of soldering. This where our focus is most usefully directed.

From experience you will have noticed that when you remove your soldering iron from melted solder it takes a few moments before it starts to change into a pasty state and then a few more moments until it properly solidifies. Also, if you have experience of different grades of solder you may have noticed that some stay in the liquid and pasty states for different amounts of time than for other grades of solder. You may also have noticed that if you move your work as soon as the solder appears to have changed from a liquid to a solid then you can be surprised to see the solder distorts and seems to turn into a lumpy grey mess (they call this a “bad joint” in electronic soldering). This all hints at there being a two-stage cooling process.

This two-stage cooling behaviour is characteristic of alloys – except for when they are in a eutectic mixture which is a special case.

Unlike pure metals, which have a single clear melting point, alloys have a range of temperatures over which they are changing from a solid to a liquid, or back again. The temperature at which an alloy changes between an entirely liquid state and a pasty state is known as the liquidus temperature. The temperature at which an alloy changes between an entirely solid state and a pasty state is known as the solidus temperature. Exactly what’s happening as the alloy cools down (or heats up) is rather complicated to explain but later I’ll give you a couple of references on the Internet you can study to find out more.

So, when we remove our soldering iron from some solder, it is in the liquid state. It soon cools down and reaches the liquidus temperature at which point it turns into a pasty state and then finally changes into a solid state when it has cooled down at the solidus temperature.

To get even closer to understanding what’s happening when we take our soldering iron away from some solder, let’s assume you have a temperature-controlled soldering iron, such as the Weller 100W, which normally operates at around 370 ºC (unless you use a different kind of tip). Let’s also assume we have a variety of grades of solder to work with – the four we are most likely to encounter.

The reason we want to know the soldering iron’s temperature is because it’s the temperature that the solders will become when heated. Obvious really!

We’re now ready to do some serious thinking. Study at the table below:

Tin:Lead Alloy Tin% Lead% Solidus Temp Liquidus Temp Pasty Range Liquid Range
40:60 40 60 183ºC 247ºC 54°C 123°C
50:50 50 50 183ºC 216ºC 33°C 154°C
60:40 60 40 183ºC 191ºC 8°C 179°C
63:37 63 37 183ºC 183ºC 0°C 187°C


If you don’t do tables and are stuck, here are some hints:

  • It has rows, one for each of the different grades of solder that we might encounter.
  • It has solidus and liquidus temperatures from which we calculate two temperature ranges.
  • It lists the pasty temperature ranges for different solders, where the solder is neither liquid nor solid. This is sometimes called the working range (a rather confusing term I think).
  • It lists liquid temperate ranges for different solders, based on an assumption that our soldering iron operates at around 370ºC.

And here are the important observations we can make from that table’s information:

  • All the alloys change from the pasty state to a solid at the same solidus temperature when cooled. This temperature is the same regardless of the proportion of tin and lead. This means that all tin-lead solders become solid at the same temperature when cooling.
  • The alloys change from a liquid state to a pasty state at different liquidus temperatures when cooled so there is link between the proportion of tin and lead and the liquidus temperature.
  • We now look at the liquid range temperatures. More tin in the alloy means a lower liquidus temperature and therefore results in a bigger liquid temperature range. This means solders with larger amounts of tin will remain in a liquid state for longer because it takes longer to cool down from 370ºC to their lower liquidus temperatures than for solders with smaller amounts of tin. This is very important!
  • The 63:37 alloy is special because the liquidus and solidus temperatures are the same. This means it does not pass through a pasty state when cooling. This property is special so it has a special name – the eutectic. If you see a solder that is called eutectic then it must be this kind of solder!

So, despite what you might read elsewhere, solders don’t melt at different temperatures. We know this can not be true because they all melt at the same solidus temperature.

Maybe those people meant to say that different solders cool at different rates. Let’s consider that as an alternative possibility. First of all we need to recognise that similar metal alloys will have roughly the same thermal conductivities. We also need to remember they are a similar colour and are similarly shiny. Our scientific thoughts therefore lead us to conclude that if they conduct their heat into the surrounding glass at a similar rate when they are cooling and emit energy as heat elsewhere at roughly the same rate by black body radiation then it must be nonsense to claim that one kind of solder cools faster than another kind of solder. If the concept of black body radiation means nothing to you then read this article.

I think it’s now time to summarise the important facts about different solders:

  • We expect 60:40 solder to remain liquid for longer than 50:50 solder which in turn should remain liquid for longer than 40:60 solder. It is differences in their liquidus temperatures that cause this difference.
  • We also expect the eutectic 62:37 solder to change from liquid to solid without passing through a pasty state. This is because the solidus and liquidus temperatures are the same.

Before you move on to compare the two main kinds of solder we use, don’t let me stop you finding our even more about tin-lead alloys. I suggest trips to and for more information.

Comparing 60:40 with 40:60 Solder

To understand which kind of solder is best for which task we first need to summarise their differences. I will only address 60:40 and 40:60 solder because 50:50 solder is nothing more than “somewhere between”.

Here are the key facts we know about 60:40 solder

  • comprises 60% tin and 40% lead
  • liquid temperature range of 179°C
  • shiny and bright
  • stronger because there is more tin

And here are the key facts we know about 40:60 solder

  • comprises 40% tin and 60% lead
  • liquid temperature range of 123°C
  • less shiny and not as bright
  • not as strong because there is more lead

The large liquid temperature range of 60:40 solder means it stays liquid for much longer whilst cooling down compared to 40:60 solder. This means a longer working time for 60:40 solder than 40:60 solder. By “working time” I mean what we as stained glass crafters have more time to “work” with the solder when in a liquid state. It stays runny for longer when we remove the soldering iron.

The longer liquid time for 60:40 solder therefore means it is best for forming long runs of liquid solder which in turn means it is good for creating long smooth solder beads and getting nice smooth joints. No excuses for lumpy areas with 60:40 solder! For the same reason 60:40 solder is also good for “re-touching” messy areas of soldering, where new and old solder need to nicely melt together into a seamless mass and hide any evidence that a problem once existed. If you like nice smooth beautiful solder beads then 60:40 is the way to go because it’s easily available and does the best job. In theory you might get a slightly better job done with 63:37 eutectic solder – and you should now be able to say why without ever having used it!

The smaller liquid temperature range means a shorter time for 40:60 solder to remain liquid when cooling. This means it is less useful for forming nice shiny deep solder beads in copper-foiled work. It does however have an important advantage over 60:40 solder in circumstances where quickly leaving the liquid phase during cooling is desirable. The most obvious example is when you are working with lead cames. We should expect 40:60 solder to be best for soldering lead cames because we want to “get in, solder the joint and get out” quickly enough to ensure that the lead cames do not start to melt.

Another example of where 40:60 solder is particularly useful is where there is a risk of solder melting through from the front to the back of a copper-foiled panel. In my experience this tends to occur more often with 60:40 solder when large volumes of solder needs to be used to fill big holes. I will expand on this in the next paragraph to illustrate how different solders look and behave differently so should be used where they are most suited.

There are rare occasions where I use both 40:60 solder and 60:40 solder for the same joint – typically where I want to fill big gaping holes between glass globs. I start with 40:60 solder to fill the larger holes because there is a smaller liquid temperature range for 40:60 solder so it solidifies very quickly (so less chance of fall-through). I leave the joint to cool. I then quickly apply a surface layer of 60:40 solder on each side for a smoother, shinier finish. It is certainly possible to do the whole process with 60:40 with deft movements of a soldering iron but I find this hybrid method convenient and less liable to fall-through. It is also possible to only use 40:60 solder for the problems joints but I find that 40:60 solder is not as shiny.

Something else I have noticed (as have other people) is that 60:40 solder seems to form deeper and more rounded beads (that are shiny) compared with shallower (and duller) 40:60 solder beads. We like shiny copper-foiled work and habitually try to dull our lead cames so again we find that 60:40 solder is more suited to copper-foiled work and 40:60 better suited to leaded light work.

One might also speculate that 40:60 solder is more likely to corrode and darken at a rate that is closer to that of lead cames than one might expect from 60:40 solder. Another reason to use 40:60 solder on your lead cames.

The higher percentage of tin in 60:40 solder makes it stronger than 40:60 solder, in terms of tensile strength and shear strength. We also know that leaded lights have lead cames strengthened by cementing. Together one might suppose that 60:40 solder is better for strength with copper-foiled work but the truth is it is of little consequence compared to carefully designing a panel for strength. It is the cementing and not the soldering that is giving a leaded light panel its strength. For comparative purposes, consider how a weak thin panel of hardboard at the back of a self-assembly wardrobe can be so effective at maintaining the shape of a wardrobe full of clothes. It’s not strong joints, it’s the rigidity of the structure.

Incidentally, another diversion is to comment that puttying and cementing do not mean the same thing. Putty is used to fit window glass into window frames. We use a cement to cement glass to the lead in our panels. Now back to the story…

So far as I can tell, 40:60 solder is not generally available for stained glass work in the USA and 50:50 seems to have become the substitute. For that reason, and by reference to the table we looked at, I would suggest the use of 50:50 as a substitute for 40:60 solder if you cannot buy 40:60 solder simply because it is the best available alternative. Do you understand why I make this suggestion?

And, of course, I’ve yet to mention eutectic solder. Can you now predict why we would want to use it?

Recall that eutectic 63:37 solder is 63% tin and 37% lead and has the special property of going straight from liquid to solid on cooling, and back again on heating, but there is no intervening pasty temperature range. The answer to why it might be useful therefore turns out to be rather simple. The lack of a pasty phase means the solder can be changed almost instantly from solid to liquid and back again simply by applying or removing a soldering iron. With deft movements of a soldering iron it becomes possible to draw and manipulate the solder to produce textured dimensional effects. The reason I say deft is because the trick is to keep the solder temperature close to the solidus temperature so that a “blobby” lump of solder will solidify almost instantaneously. Isn’t it great that a little scientific thinking can explain how to do “decorative soldering” without having to pay someone to show you?

Another reported advantage for 63:37 solder is to bead the outside edges of copper-foiled pieces. Again, the trick would seem to be not letting the solder get too hot and runny. In truth I’ve never ever tried 63:37 solder so I’d be interested to hear of your experiences. Theory isn’t everything. Every hypothesis needs testing!

Different Solder Forms

You will find solder widely available in a solid core wire form on a spool or reel, and the amount of solder on a spool may vary. So far as I can tell, this is the only form in which solder is available in North America. Historically, this is the form used by plumbers and for electronics. In electronics they tend to use rosin-cored solder and it is nasty stuff that is not suited to stained glass work because the flux is acidic and leaves a horrible mess.

In other countries solder is also available as “blowpipe” stick. You will also find “tinman” sticks (which are more like bars) but they are rather too bulky and crude to use for stained glass crafts.

I prefer to buy my solder in the blowpipe stick form rather than on a reel. I find it more convenient to use blowpipe sticks because they are easy to handle and lighter than a reel of solder. If you can’t get blowpipe solder try cutting lengths from your reels and see why I prefer blowpipe sticks.

British Standard Classification

There is a British Standard (BS219) classification system for tin-lead alloy solders that nicely eliminates the confusion about 40:60 vs. 60:40 that I describe later.

In this particular classification system blowpipe sticks are given a letter code. It’s much easier to ask for “K stick” than “60:40 solder”, “F stick” rather than “50:50 solder” and ask for “C-stick” rather than “40:60 solder”. No scope for confusion and you are sure you’re getting what you really wanted.

Visit this UK manufacturer for more information about this classification system.

Solder Grade Availability

We know there are different grades of solder and I have already alluded to a suspicion that you can’t easily get 40:60 solder in the USA.

If you are in North America the commonly used solders in stained glass seem to be 50/50, 60/40 and 63/37. If you are elsewhere you are may to find the 40:60 alloy as well. Curiously, I could not find any reference to 40:60 solder in North American web sites (but did once spot 30:70 being mentioned in passing).

But beware. Although 60:40 solder ought to mean an alloy of 60% tin with 40% lead, some people (and some suppliers) get confused and inadvertently reverse the numbers. If you have any doubts ask them “does your 60:40 solder contain 60% tin or 60% lead?” and if you can’t get a sensible answer try looking at the price – higher proportions of tin result in higher solder prices because tin is always more expensive than lead as a raw material.

Lead and Purity

You will find comments in various places on the Internet that tell you to look for solders that are “free of impurities” in the component metals. You will also find comments that warn you that impurities cause a “scum” on your solder beads, that they degrade soldering iron tips, and interfere with the proper reaction of patina chemicals resulting in undesired finishes. You will also find advice that tells you to insist on lead and solder that comes from virgin lead, meaning not recycled. And finally, you will see comments about one brand of solder being better than another because it doesn’t make use of recycled materials.

If you look here you will discover that lead has one of the highest recycling rates of all materials in common use today. Recycling rates of 100% are achieved in some countries and others are not far behind. So the chance of finding lead cames and solders containing only virgin lead is rather optimistic. All that we need to do is be vigilant and not buy dodgy solder from dodgy suppliers.

I am dubious about the claim that some solders degrade soldering iron bits. The only significant causes of soldering iron bit degradation I am aware of are over-use of soldering iron tip cleaning materials (such as sal ammoniac), the use of acidic fluxes and the long-term use of damaged tips.

I doubt the claim that some solders interfere with patination chemical processes. Patination chemicals react with the lead and the tin in the solder so all that the patination chemical needs to find on the surface of a solder bead is tin and lead to produce their surface effects. Only if the soldered surface is not clean or the solder is massively contaminated can I see this problem arising.

Comments about impurities in solder causing a “scum” on solder beads I find hard to believe and I have neither seen nor heard any tangible or verifiable evidence for it. I have certainly seen impurities causing a scum on solder but they have washed away on cleaning and are more likely to have originated as lead and tin oxides that have naturally developed on old lead cames, muck from a dirty soldering iron, zinc from safety flux, muck on copper foil or maybe even copper compounds from old copper foil.

It is however worth mentioning that some solders, not intended for stained glass use, may contain other metals in their alloy. Be sure to avoid anything containing cadmium, antimony, or other really nasty elements. Not that I’m saying lead is particularly healthy!

Solder Fluxes

A slight detour into solder fluxes for use with solders is perhaps useful.

Fluxes are materials that help us join one kind of metal to another. There are many fluxes and many kinds of metal. The important this is that we use the right kinds of fluxes for the metals we are using and avoid the ones that might cause us problems.

The first important thing to remember is to never ever use rosin cored solder or rosin as a flux. Notice the word “rosin” because it is not the same as “resin” as some people might suggest. Rosin cored solder is used widely in the electronics industry. The rosin core is acidic and leaves the brown resinous deposit you might have seen on a circuit board.  It also produces a nasty vapour which can sometimes be seen as a white powdery deposit. If you try to use rosin as a flux, or rosin cored solder for stained glass work you will be left with a mess that is not easy to clean off.

I doubt I am telling you anything you don’t already know, but 40:60 solder is best used with tallow as a flux and 60:40 solder is best used with a non-acidic safety flux.

Tallow is an interesting old substance – it is derived from animal fats so I guess vegans might not want to use it. This in turn makes me wonder whether a leaded panel is a suitable gift (or purchase) for a vegan.

If you want to make your own safety flux then look here for more details. It’s easy, cheap and exactly the same as many commercial formulations.


There is no difference between different kinds of solder in terms of how well they take patina. What really is important is the thorough cleaning and preparation of soldered panel in anticipation of patination.

If you need to make your own copper patina or want to know how it works, look at this article.

Choose Performance, Not Price

So, it’s finally time to pull all the information together and reach some rational conclusions about why to choose one kind of solder over another for a particular purpose. It’s time to summarise.

The cost of each grade of solder depends on the relative amounts of tin an lead in the alloy because the underlying prices of lead and tin are very different. So, the price depends on what’s in the solder and does not imply anything about performance or behaviour. Nearly all the lead we use is recycled so trying to find solder made from virgin lead is optimistic. Buy a reputable brand from a reputable supplier if you are concerned about the quality and performance of your solder.

Choosing a grade of solder ought to be based on how it behaves and how it performs if craftsmanship is your primary concern. You should not be choosing a grade of solder on the basis of price unless you are cash-strapped and are prepared to compromise on the quality of your work.

These are what I believe to be rational reasons to choose each common grade of solder:

  • The 40:60 solder is best suited for work with lead cames because it stays liquid for a short time when cooling and produces duller results than 60:40 solder. It can also be useful for copper-foiled work to reduce the chance of fall-through when bridging large gaps.
  • The 60:40 solder is best suited for copper-foiled work because it stays liquid for a long time when cooling and can produce smoother and shinier beads.
  • The 50:50 solder is a compromise if you cannot buy 40:60 solder. It is not as good as 60:40 solder for copper-foiled work because it does not stay liquid for as long.
  • Eutectic 63:37 solder may be useful for fancy decorative soldering work because it will instantly solidify during cooling without passing through a pasty stage.

And finally, only ever use a suitable flux. There are many commercial varieties of safety flux that are suitable but the recipe I give you here for copper-foiled work is cheap and as good as the competition. Use tallow for leaded panels if you are not a devout vegan. Never use rosin as a flux, or rosin cored solder.

More Information

For more information about solder, visit For a alternative source of good information about solder, as well as copper foil and other related products visit – but do bear in mind it’s in their interests to promote their own products. Other products and suppliers do exist!


Posted in Flux, Patina, Solder, Soldering | Tagged , , , , , , , , , , , , | 3 Comments

Etching and Engraving Dichroic Glass

Photo-0003 Etched & Engraved BlogWhilst browsing around the Internet recently I encountered comments about etching dichroic glass. I found plenty of vague and conflicting comments about what to do and what to expect.

So today’s posting is about some experiments I have been doing. I hope it leaves you with a clearer understanding of what you can do and what to expect.

If you’re a regular reader of my blogs you will realise that you don’t get away without some science somewhere or other in my postings. The connection I want you to make on this occasion is that dichroic glass works in exactly the same way as a droplet of oil on water, the wings of a butterfly or the carapace or a beetle. They all produce vibrant colours when, in fact, there is no pigment or dye producing those colours. The underlying physics is thin film light interference. If you’re interested learn how colour can come from something colourless then I recommend a visit to and for more information. You may also find it interesting and informative to visit for some general background reading about etching and engraving methods.

As far as my own experiments are concerned I have tried two basic techniques – etching and engraving. The difference between them is that etching is a chemical process whereas engraving is an abrasive process, each of them aiming to strip away a very thin metallic layer from dichroic glass. With reference to the picture I will describe each method in turn.

There is no reason why you should not try this even if you only have a little microwave kiln.

Etching Dichro

The dangers associated with hydrofluoric acid are well known and it takes a brave person to work with this particular acid. Despite what you might have heard, hydrofluouric acid can be obtained in the UK, from places such as APC Pure (at I mention APC Pure simply because they also supply a variety of other products that happen to be useful for glass workers but do not charge daft prices that you’ll find at most stained glass suppliers. Examples are acetone and isopropanol (for cleaning glass), copper sulphate pentahydrate (to make copper patina), wash bottles, buckets, bottles and jars. Other than being a customer, I’m not connected to APC Pure.

But I digress. Back to etching…

For small-scale gentle acid etching there are several brands of glass etching cream. An oft cited brand is Armour Etch. These creams are relatively safe and easy to use even though their underlying chemistry is no different than hydrofluoric acid. The difference is that the creams are very much weaker than hydrofluoric acid.

I tend to use a paintbrush, cotton bud or a plastic sponge to apply glass etching cream. When I remember, I use cheap plastic disposable gloves to protect my hands. Only if you are a messy worker should you consider additional precautions.

I have found that the metal coating of some kinds of dichroic glass will etch away completely in a matter of seconds whereas others can take 20 or even 30 minutes to etch away completely. It is only by experimenting that you will discover what to expect. My suspicion is that some types of dichroic glass have a protective glass layer on top of the metallic coating but some do not, that some metal coatings will be thicker (or thinner) and that some metal coatings are more susceptible to acid etching than others (eg see Reactivity Series at Wikipedia). It is certainly the case that CBS Dichroic (at mention that their standard colours have half the number of metallic layers than their premium colours as well as saying they apply a quartz crystal protective layer. The results of etching dichroic glass will therefore depend on all these factors.

To stop the etching process is easy. You can optionally begin by wiping away excess etching cream with a paper towel. The important step is  immersing and cleaning the glass piece in water. If the etching cream is not cleaned away completely then it will continue to etch the glass.

In the top right of the picture you will see four small oblong panels that took only seconds to reach a state in which some metallised areas are partially etched away and other areas have no metal coating whatsoever. I used a small paint brush to apply the etching cream and almost immediately washed away the etching cream, repeating the process if necessary. Evidently these dichroic glass had little or no protective quartz above the metallisation and/or had fewer or more reactive metallic layers.

The results are rather interesting in that the degree of processing results in different colours, or black if the metallic layer is completely etched away. The reason for different colours can be related back to an expectation that light interference will change when the dichroic layer is partially etched away.

Below and to the left of those four small oblong panels are examples where the etching was very slow, resulting in nothing more than subtle colour changes. The blue finger to the left has also been engraved to enhance the colour change effect.

To the left of the blue finger are two pieces of dichroic glass, one with a floral pattern and the other with a starry pattern. For both these examples two craft paper punches were used to stamp out self-adhesive plastic shapes that have been applied to the dichroic glass to act as an etching resist. This particular colour of dichroic glass took a looooong time to etch. If you look very closely at these two pieces you will see that the black areas do still have a little of the original dichroic coating remaining – and it is the same colour. I love the starry example as the feint wispy effect gives the impression of a starry sky with wispy clouds.

The last remaining example of etching is in the middle of the picture, where bands of varying width have been etched away. This could also be done by engraving.

What I want you to realise is that etching can be used to change a plain single-coloured dichroic glass into a multi-coloured dichroic glass.

Engraving Dichro

Examples of engraved dichroic glass can be seen mostly to the left and at the bottom of the picture. The finger of glass at the bottom left of the picture is the exception because it is engraved iridised glass – a hint that you can also engrave iridised glass!

The purpose of the experiments was to see how different line widths and different types of patterning would turn out. I was not out to impress you with artistry.

Dots, squiggles, thin lines, thick lines, regular patterns, irregular patterns. They all seem to lift a boring piece of plain dichroic glass into something more interesting.

I am particularly fond of the two colourful oblong pieces towards the lower left of the picture where fine engraved lines have been used to allude to the contour lines and colours of a map.

It is a simple process to engrave dichroic glass. You will need a light and comfortable hand-held electric drill (such as from Dremel) and some diamond coated burrs. You may also find it useful to consider a “flexible shaft”, particularly if you find handling a drill too heavy and cumbersome.

The type of diamond coated burrs I find most useful have a spherical ball-shaped tip because it’s easier to use them. They grind away the same width of line no matter how you’re holding the drill or in which direction you are travelling. Different diameter ball-shaped burrs produce different line widths.

It is also possible to adjust a line width by applying more (or less) pressure but resist the temptation to apply more pressure because it will shorten the life of your diamond burrs. Better is to change to a different sized burr.

The reason to use water (or oil) lubrication with diamond tipped burrs is mostly about keeping the diamond grits cool and washing away abrasive waste materials – the objective is therefore to extend the life of the burrs. Also important is to recognise that the diamond grit coating will be stripped away due to friction if more than a light touch is used. This is why you get told to let the diamonds do the work and are told not to hurry the process by applying pressure.

But you will see from the examples that we only need to scratch away a few thousandths of an inch of dichroic coating over a small area of glass. This means the diamond grit coating will not get too hot. Not unless you are applying pressure and trying to hurry the process. In turn, this means heat caused by friction should not become a problem, just as large amounts of abrasive grinding waste will not be a problem. Therefore, it is OK to engrave without the use of water or oil. But beware the dust thrown up by dry-engraving glass and use a respirator if you want to avoid silicosis.

Finishing Off

At the end of your work session you will find that everything you have etched and engraved will have a dull-black surface caused by the etching and abrading. This can be resolved by fire polishing (as shown by the various circular and finger shapes in the picture) or by capping with clear glass (as shown by the various rectangle shapes in the picture).

Remember to dispose of etching cream laden paper towels and other waste materials carefully. Also thoroughly clean your brushes or the acid will continue to etch any metals they come into contact with.

Some Conclusions

Different kinds of dichroic glass will behave differently when a glass etching cream is used. Armour Etch is an oft quoted brand but there are several others that also do the same job. Glass etching creams work in the same way as hydrofluoric acid but are much safer and easier to use.

Some kinds of dichroic glass metallic surfaces will etch away very quickly but some will take a long time. It is in the nature of how a particular piece of dichroic glass has been made that causes this difference so pre-testing small scraps of dichroic glass is the key to discovering how fast a particular dichroic glass will etch.

Partially etching plain dichroic glass, using a brush stroke or cotton bud smear will result in a multi-coloured dichroic effect that depends on the degree to which the surface gets etched. Rinsing and cleaning the glass piece in water will stop the etching process immediately. The colour changes in a partially etched surface are the result of light interfering in a different way. Although difficult to control and predict, it is a novel way to change plain dichroic glass into something unique and interesting.

When “resistant” dichroic glass is being etched, it is more easily possible to stop the etching process at a desired state. It is possible to cause only subtle colour changes across the surface, which can be made more exciting by engraving contours around the different coloured areas.

Self-adhesive plastic can be applied to the dichroic glass surface to resist the etching process so that neat well-defined shapes and patterns can be produced for decorative effect. It is also possible to stop the etching process just before the whole dichroic coating has been removed from unprotected areas, at which point there will be a wispy patchy effect. This has been illustrated by the “starry sky” example.

Engraving dichroic glass can be achieved with a hand-held electric drill and diamond coated burrs, ball-shaped burrs perhaps being the easiest to use. Lines engraved away from the dichroic coating can be made thicker and thinner by using different diameter burrs. With due care and consideration dry engraving is a suitable method.

A fire polish or capping with clear glass is necessary to return etched and engraved glass surfaces back to a glossy state.

That’s all. Your turn to experiment!

Posted in Dichroic Glass, Engraved Glass, Etched Glass, Experiment, Microwave kiln | Tagged , , , , , , | 3 Comments