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.


About chatterglass

Maker of stained glass frippery.
This entry was posted in Experiment, Microwave kiln, Money-saving ideas, Mould, Stringer and tagged , , , , , , . Bookmark the permalink.

4 Responses to Stretch, Bend and Squiggle

  1. Pingback: Repairing a Broken Mould | Chatter Glass

  2. Could I use a torch to heat some COE90 thin rods to make some squiggles? I need tiny squiggle shapes for a mini kaleidoscope I’m making and I saw that Hobby Lobby carries thin glass rod.

    • chatterglass says:

      I’ve not done torch work so can only guess that it would require some deft skill in such a hot flame. For little shapes using 1mm and 2mm stringers I’d recommend a spirit burner or a candle flame because their flames are not so fierce and you’d get better control over what happens.

      Remember also that you could trap things like bullseye Thinfire paper, Glassline papers and copper foil between glass layers to get solid shapes. You could also try a little copper oxide (optionally with a touch of cobalt oxide) for blue bubbles that really catch the light like little lenses in bright sunlight. Refer to other blogs for details on these. Good luck with your kaleidoscope. I hope it turns out well.

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