COE
CONFUSION OR EFFECTIVE
What it means is coefficient of expansion. It is a measurement of the rate that glass will expand and contract when it is heated and cooled. In the good old days, we just lived and died by put 90 COE together or put 96 COE together. It did seem to work. It has become more complex. It is now a guideline not a "live by, die by rule". First now we hear about a lot more coes.Window glass (float glass) is somewhere between 84-87.
![](https://cdn.shopify.com/s/files/1/0681/9781/0478/files/Pic-1-300x189.jpg)
A bottle could be anywhere between 82-96.
![](https://cdn.shopify.com/s/files/1/0681/9781/0478/files/Pic-2-300x248.jpg)
Now we also deal with hot glass. The soft rods, glass and accessory are 104 COE
![](https://cdn.shopify.com/s/files/1/0681/9781/0478/files/Pic-3-300x263.jpg)
This direction from Bullseye tech tips.
“Whereas expansion affects the compatibility
predominantly in the lower temperature range—below the
strain point—the viscosity properties affect compatibility
predominantly in the annealing range, from the annealing
point to the strain point. Differences in viscosity between
two glasses will cause compatibility problems. If one glass
is stiffer than the other, they will strain each other as they
cool through the annealing range.”
How can you know if your breakage occurred when annealing or fusing? If the break is sharp it broke during cooling (annealing). If the break is smooth over it, then it was still fusing after the break. So, what to do? If you are going to mix manufacturers, you need to test. They may be compatible. They may not.