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Clay & Glass

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#21 BetsyLu


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Posted 23 December 2013 - 01:54 PM

If it helps, you may want to research pate de verre. It is fine glass frit mixed with a binder (usually gum arabic) and made into a sort of paste, which is then pushed into a mold (usually plaster and silica). It may be a more forgiving way to incorporate glass, but it is a technique to master in itself. (I haven't done it myself, so I can't give any personal experience here.) 


I would recommend picking a specific kind of glass and sticking to it. Using glass meant for stained glass will lead to frustration, as each piece has a different COE and is thus incompatible with other kinds of stained glass. Plus you'll have to develop a kiln schedule for each individual piece of glass. I would recommend using one of the more expensive but more reliable brands meant for kilnwork- Spectrum has a COE of 96, and Bullseye has a COE of 90. There can still be slight incompatibilities but not nearly as bad as you get with "found" glass. One other thing to keep in mind, though, is that glass from recycled bottles has a higher melting point than these glasses do and thus might be better suited for ceramic work. It's tough to find a good kiln schedule for it, though. 



Here are some basic starter schedules for each kind of glass. You'll notice that the temperatures and time are very specific. That keeps the glass from getting thermal shock and cracking. There are 2 very important parts to how glass responds to heat: how hot it is, and how long it is held. 


Remember that you'll need at least a tack fuse to get the glass to stick to anything- at a slumping temperature it is not molten enough to bind to other glass or materials. Glass slumps before it fuses, so keep that in mind! Don't expect perfectly cut squares to stay put and keep their shape on a curved surface, for example. :) 


Hope that all made sense and is helpful!

#22 BetsyLu


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Posted 23 December 2013 - 07:10 PM


When mixing glass with ceramics, you need to understand that the COE needs to be converted.


For no good reason, Glass COE is measured in inches per degree C.  Glaze and clay COE is measured in meters per degree C.


So COE 96 glass has a ceramic COE of 2.44.

If I've done the math correctly, 96 x 10-6 inches per degree C, is 2.44 x 10-6 meters per degree C.


Here's how COE 96 glass compares with other ceramic material.


COE Expansion
7.86    Zam Celadon Glaze
6.99    New Zealand Frost Clay (Laguna)
6.74    Oribe Celadon Glaze
5.60    Hagi Porcelain (Laguna)
4.64    Amador Clay (Laguna)
2.44    Glass COE 96 - This intentionally shivers inside a New Zealand Frost orange slice.

Adjoining COE 96 glass is made into ceramic compatible sauce, without shivering or crazing, by mixing with high-expansion Ferro Frit 3195.



Have fused stain glass to pottery, however I always use it as kind of a second glaze, if that makes sense. How do you imagine the stain glass to be connected to the clay? Just to help me imagine the effect you want. Matt is right its tricky to find the COE but do able. T



Really good info there, thanks for sharing! Do you know if there is a way to lower the COE of ceramic so you don't have to add anything to the glass? (I'd presume you'd have to use glass powder or fine glass frit to mix anything with it, and for those people who want to use sheet glass it might be interesting to adjust the clay instead?)

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