Tips from the Glass Academy: COE


COE: What the Heck Does that Mean?

“COE” stands for Coefficient of Expansion.

What does Coefficient of Expansion mean? It is the fractional change in length or area or volume per unit change in temperature at a given constant pressure.

What does that have to do with glass? Glass expands when it gets hot and contracts when it cools, which results in a change in density. Measured in a lab, this figure would be miniscule and very, very long, so for ease they are shortened into whole numbers. The most common we see are 90 COE and 96 COE. We also see 82 COE. Bullseye Glass is thought to have a COE of 90 and Spectrum System 96 has a COE of 96. Window glass has 82 COE from some manufacturers while other manufacturers might be a few points difference. Glass rods are 90 COE, 96 COE, 33 COE or 104 COE.

Why does it matter? Well, maybe it doesn’t to you. If you are not heating and merging the glass, no worries. If you are foiling or leading – go right ahead. Mix and match – have at it! However, if you are fusing or flameworking, then it is very important. Keep your COE’s separate or you will have breakage. It might break in the kiln or it might break days, weeks or months later. Not cool if you are about to serve oysters on the half shell on that new glass platter you just made!

Click here to view all of the 90 COE and 96 COE glass sheets we stock.


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