Glass Creations

[Diane Stafford]

I have started this Glass group with member Dawn's post, which gives a great starting point:
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by Dawn on March 22, 2008
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I am not an expert by any means, on glass, but I will share what I know

So a few answers to a few questions - glass melts at DIFFERENT temperatures, depending on what has been added to it. Pure glass (silica) needs temperatures of around 2000 centigrade - but most glass has fluxes to lower this to workable temperatures.

Most "art glass" such as Spectrum or Bullseye brands, is workeable in some form or other from around 600 cent (softening) to around 925+ centigrade (melting).

One of the most important things about working with glass is compatibility - glass has a coefficiency rating (known usually just as COE) - and to put any two or more glasses together, they need to have the same COE (glasses of a slightly different COE can be used in small quantities)

So, something like Bullseye is COE 90 - Spectrum is COE 96. Most lampworked glass, used for beads is often 104 - but you can use a small amount of a different COE glass as an additive - but not much,

COE is to do with rates of expansion and contraction - so when glass is heating and cooling, it is moving around - different COEs of glass do this at different rates - so mixing glasses of different COEs results in stress and cracking as the 2 glasses are moving at different times and rates.

I don't know the COE of bottle glass. It differs from manufacturer to manufacturer, from colour to colour and from country to country. So American green bottles could well be a different COE to UK green bottles - blue different to green, etc. There is usually little need to publish COE figures for bottle glass, as it only usually has one purpose. But you might be able to find the figures from somewhere on the tinternet.

There are definitely schedules around for working with bottle glass - artists have slumped with it, and made beads with things like Bombay sapphire gin bottles - and there are annealing schedules out there.

Annealing is a most important aspect of glass work, it is what releives the stresses and adds the strength. Glasses have different annealing ranges.

There are other things to consider too - float glass (window glass) is usually made on a bed of tin - so it has a "tin side" which can be prone to clouding, devitrification and other things.

Lots of experimentation is what is needed - especially if working with an unknown quantity like bottle glass -

There ARE special glass ovens - but you can use a ceramic kiln, however control is important - you'd struggle with the normal kiln sitter and cones. Not impossible, but having control over ramp rates, hold times, etc is imperative to glass - so you could use a ceramic kiln or even an enamelling kiln, so long as you can control the temperature somewhat.

Recycling glass is a fantastic idea - although, as glass is a plentiful resource from the earth, like clay (well it is silica), don't rule it out - as much energy is probably used in recycling than is used in bought glass - and all glass, bottle, art or architectural, comes from sustainable, renewable resources.

As for Paperclay, Diane, once I have done my initial experiments with types of paperclay, I want to work with fusing glass to unglazed and probably also glazed clay forms - and to perhaps try embedding glass into clay, and so on - there is so much to try!!

I know very little about ceramics, and I am new to glaze technology too - I have yet to discover how glass can be incorporated into clay/paperclay bodies - I am looking forward to seeing what happens with different combinations and at different temperatures.

Hope some of this is helpful - if it doesn't make sense, please message me and I will try and answer your questions when I haven't been to the pub!!

I love glass, and I love the endless possibilities of what you can do with it - there are SO many glass artists out there doing so many different things - the possibilities seem endless - and that is glass alone - combining opens up even more opportunities!

[Diane Stafford]

Dawn, thanks so much for your detailed response to the glass question. I have started this group specifically for those of us interested in working with glass in some way. Like you say, much experimentation is required - and I for one am not quite sure where to start.

I want to use small pieces of glass embedded in paperclay / normal clay in a variety of ways and would love some advice on where to start. One thing I 'visualize' is - whats the name of that drink they put salt on the rim ? - anyway something like that - with the glass powder/tiny pieces dipped onto the (wet) rim of a pot and fired - but what temperature would i fire to???

Any suggestions would be helpful thanks lots Di

[Dawn]

Hello Di

Glad the info was useful (not bad for a Friday night....)

Is it a cocktail your'e thinking of? No, I can't recall it, either, but I can picture the frosted rim.

I am not sure what happens to glass that is fired to clay temperatures - it would melt, I expect, how much by, I don't honestly know. I think someone at Uni previously tried glass embedded into the clay body walls, and I think it kind of splattered - unfortunately I never saw it, it was before I started. Sounds interesting to me!

I am not sure what would happen to tiny pieces, or powder, at clay temperatures - whether they would melt into glaze? What temperature would you fire the clay to? Would it be possible to biscuit fire, then refire with the glass perhaps?

When you get to temperatures of around 750c, the glass would start to tack fuse - Bullseye fully fuses at about 800c - but that is to itself - it still isn't molten, its just soft.

A friend cast a medium frit into a mould, and at around 800, you could still see that it had been granules - it retained its frosted effect. I think Pate de Verre (thats paste) is fired at around 850c - at that goes kind of frosted but smoother.

At around 925c you can pot melt, where the glass becomes runny and different colours will join into another and form a solid piece of glass.

This is of course, the glass to itself - if it were embedded into a clay body, then it would have nothing to fuse to.

So, if you were to use an earthenware body, would you fire that to 1000c? That isn't much higher than the melting temperature of art glass, and float (window) goes higher than that (around 40c for each process) - so its possible that the float, or probably bottle glass too, wouldn't fully at these temperatures.

One thing that you could consider too - I don't know with clay how quickly you fire - do you have to hold it at temperature? Or is it a case of taking it up to the required temperature and straight back down again?

Glass firing often involves a hold at the process temperature (referred to as process soak) - so perhaps you could avoid glass melting into oblivion if you don't have to hold the temperature for long?

It all sounds very exciting, I can't wait to have a go too!

[Diane Stafford]

Brilliant information, thanks Dawn, yes I can fire bisque first then add glass and or glaze and fire to earthenware with or without a soak/hold - hmm... think I would be tempted to test inside a bowl shape just in case there is some 'running' and to avoid ruining my kiln lol :)

I'll see what glass I can get hold of and give it a go. I may test various temperatures to see what the results are, with and without glaze may prove interesting too.

thanks again, will let you know the results

[Dawn]

I want to try slumping glass onto/into paperclay (which I would pre-fire) -

Usually, if you use a clay mould (as opposed to plaster), you'd kiln wash it first to prevent sticking.

I'm curious as to what would happen to glass slumped into bisque, glazed and unglazed.

The glass wouldn't melt, but I am interested to see how much it would stick,

Di, avoid using any tempered or safety glass - the way it is treated means it could explode (car windscreens are fired and rapid cooled so that there is different tensions surface and interior - but firing them isn't good!)

I go to my local glass merchants and give them a box and ask them to put offcuts into it.

Wine bottle glass of course, although they are all slightly different COEs - but for your project, it sounds like different COE glass could work wwell,

So long as you kiln wash your shelf well, the glass shouldn't stick. You could always try a bit of ceramic fibre paper, - minimum 3mm as a shelf liner - would last a few firings and definietly stop any glass drips

[Diane Stafford]

Brilliant thanks Dawn, I'll be careful on the glass type, good advice. Probably being overcautious on the kiln front, however I'll get some of the ceramic fibre paper this week and kiln wash it over as well :>)

will let you know when i do some tests,

thanks