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I've been working with cold glass for a few years and have recently purchased a kiln. I have a small amount of both COE 90 and COE 96 glass and am preparing some test firings. I understand COE and that you don't mix different COE glass in the same project. However, I'm also planning on doing some tests using some of the non COE rated glass that I've accumulated over the years. As long as I use pieces from the same sheet of glass for a project, are there any reasons that I cannot use that glass?

Thanks,
Bill in KY

It depends. I've had the best luck using Spectrum and Bullseye glass - again, the same sheet melted together. Ring mottles and streakies tend to turn rather unpleasant poop colors. But, please experiment. I once knew a lady who successfully fused light blue ring mottle glass to make snowflakes.

Bill, you have to test. The big reason you might encounter problems is that before fusible glass, the formulas used were not maximized for re-heating. So, they tend to be far more devit prone than glasses formulated for fusing. Opals will be more problematic than transparents.

Lesson one in fusing is that COE is only one factor that determines compatibility. Viscosity is another. These can work to balance out stress, or increase it. Chances are, compatible glasses have differing COE's. Also COE changes in different temperature ranges. What happens at 300 could be totally different from what happens at 700ºF.

Bill, The main problem I ran into was color change. Some of those beautiful glasses that are not manufactured for fusing can change color when fired. A mottled glass may lose it's mottles. Some do fine. I enjoyed messing around with that type of glass while getting acquainted with my kiln but very quickly the the time lost and frustration with consequences led me to stick with the relatively more predictable world of compatible glass.

Welcome to the board.

WASTE OF TIME!! Don't sell anything you make!!

I disagree....i have bought out a few glass buisnesses over then years that have gone under and ended up with quite a bit of nonfusable spectrum. Because of that we did alot of testing........We found that around 80% of it is fusable to 96 clear without stress although it is very devit prone. You can combat that by always capping with clear or spraying with devit spray.
The glass that did not work with 96 was fusable to itself with spray for devit although some of it changed to darker unpleasant colors. It is all about testing but well worth the work if you have the glass. Some of it was so nice that I bought more......
That being said I would never use nonfusable in something like pot melts or pattern bars......

If you are making stuff for yourself, and if you have time on your hands go ahead and test, test, test.....But if your time is valuable and your reputation as a glass artist is important don't do it! I would never send anything to a gallery to sell that was less than quality work.

Laurie Spray wrote:I disagree....i have bought out a few glass buisnesses over then years that have gone under and ended up with quite a bit of nonfusable spectrum. Because of that we did alot of testing........We found that around 80% of it is fusable to 96 clear without stress although it is very devit prone. You can combat that by always capping with clear or spraying with devit spray.
The glass that did not work with 96 was fusable to itself with spray for devit although some of it changed to darker unpleasant colors. It is all about testing but well worth the work if you have the glass. Some of it was so nice that I bought more......
That being said I would never use nonfusable in something like pot melts or pattern bars......

Just curious--how did you test?

Tested using coe96 clear over regular spectrum using a filter to view. Some had obvious halos.....obvious which had problems. I am talking transparents here of course.

I also used Spectrum mostly transparents for many years with out using 96... it's all about testing...