Mixing Glass Coefficient Ratings? Nope
Producing the best quality glass products requires attention to several details.
Producing the best quality glass products requires attention to details.
All glass expands and contracts as it is heated and cooled in the kiln. This ‘movement’ is called “Coefficient of Linear Thermal Expansion” (CTE). Ouch! Sorry about that..
Let’s just call it ‘CTE’ to keep it simple…
Every piece of glass has a CTE rating. “Bullseye” Glass is the brand of USA made glass that I use in all my production and has a CTE rating of 90. Other glass might be 96 or whatever number is assigned. Okay - I heard you say - who cares! That hurts… Well, if I mix my 90 with 96 or some other number, it will probably shatter or crack. Ohhh, I get it! :)
And here is the science being it -
Consider TWO pieces of colored glass with different Coefficient CTE ratings being fusing together. If the kiln’s temperature is unevenly applied to the glass (which heat movement constantly happens inside a kiln) - different areas of the glass will expand and/or contract by varying dissimilar amounts (its like a battle of ‘movement’ between team 90 and team 96) - and the ‘movement’ result will create internal stresses which cause cracks, fractures and failures. Now we don’t want that do we! We like our glass to be happy and dancing in rhythm!
The idea is to keep your glass Coefficient rating the same and not mix the numbers. You get a much better quality product when that happens.
Now you can say, “Who cares!”
Happy firing. Tom