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Why do I need to know about COE for fusing glass?
This is a very important issue when it comes to dealing with warm glass or fusing glass. Fusing glass comes in a variety of different types and you need to make sure that your glass is compatible or when you are done fusing you are going to have a project that is a mess, probably even cracked and broken up.

The thing to look at when you are purchasing a fusing glass is the COE or coefficient of expansion. If you pick one type for a project, all the glass needs to be of the same COE. In our shop we use 96 COE made by Spectrum or Uroboros and is called Spectrum System 96 glass. It is a thinner glass and is also tested compatible. The other glass is a 90 COE – This glass is commonly made by other companies. If you purchase both types of COE make sure that each type of glass is marked appropriately so you don’t mix them up.

Below are other types of glass used in fusing always making sure they are compatible:

Float glass: This type of glass can vary quite a bit. So make sure that when you do purchase this buy more than enough to do your project; again, don’t mix your glass. This glass is easily found and is inexpensive to purchase.

Dichroic – This glass is a very stunning glass and can be rather pricy, but for those special projects like jewelry it can make a world of difference. When the glass is made very thin layers of chromium, silicon, titanium, aluminum or zirconium are put on the glass in a vacuum chamber at high temperatures creating spectacular colors. This glass was actually invented by NASA and was used as a interface filter of some sort.

Iridescent - It has a surface treatment that gives it a rainbow like appearance.

Regular Stained Glass – This glass is not normally tested so compatibility is an issue. However, we did speak first hand with Spectrum Glass and we were told that all their glass is a 96 COE. The difference with their actual SYSTEM 96 glass is that glass is actually tested. All regular stained glass can be used for fusing, but you can’t mix glass that’s all. If you have the time and want to test compatibility you can try and fuse small items to see what happens. However, there is a high possibility that you won’t be able to use different colors to fuse together. You can slump this glass into molds, or use it for draping purposes.

I could go into the entire chemical and scientific reasons why, but after about 2 minutes of reading it you would fall asleep. So, suffice it to say DO NOT MIX COE’s pick one and stay with it for each project.

Hope this helps!