I anneal bottle glass at 955 degrees for several hours. From what I've been able to find out, the COEs range roughly from the high 80's to 90. It seems to work; some of the beads on that string of bubbles have been there for years without cracking, and I haven't had any trouble from more solid pieces either. As for large pieces, well... I haven't tried to make anything larger than about 1 1/2", so proceed with caution.
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