Can I fuse or cast Bullseye with any COE 90 glass?
The answer to this question is not simple. Our short response is this:
Matching COEs does not ensure compatibility between glasses, in spite of what you've read or heard from other practitioners or glass manufacturers.
Bullseye's fusible glasses are factory tested for compatibility with each other. We do not test for compatibility with other manufacturers' glasses. We do not test for COE or rate our glasses with COE numbers. We do not claim to produce glasses that are rated "COE 90."
The ONLY way you can insure that a Bullseye glass will be compatible with another manufacturer's glass is to conduct your own tests.
We recommend that you read TechNote 3: Compatibility of Glasses, which explains this complex and important matter in greater depth.