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Old 04-02-2005, 02:31 PM
Lani McGregor
Posts: n/a
Marc, Oh good, Mr & Mrs Schuler weren’t bongmakers by trade. Whew!

But the earlier statement "When glasses are mixed, it is important that they have the same coefficients of expansion, so that stress is not set up at the interfaces between the different glasses after cooling" is still without enough qualifiers to be applicable to all studio glass situations.

Primary missing info here is:

1. What glass were the Schuler’s working? Were they mixing glasses with the same annealing points (i.e., the same viscosity)? If so, the statement is undeniably true.

2. Does Schuler mention which COE he’s talking about? 0-300C? Or a COE for instance in the 500-530C range?

So much of the problem today, as has come up earlier in this thread, is with the mixing of color where the viscosities – which are indicated by the AP - are often so different. Finding any reference in the technical literature to compatibility issues in mixing colored glasses of different base compositions is close to impossible.

The other problem with part of this discussion is a semantic one: the mismatch of glasses is commonly referred to as an “expansion” problem, but the term “expansion” used this way refers to the strain between the glass, NOT to the LEC of either or both glasses. This expansion difference (or strain) is not solely the result of LEC differences.


PS. Marc, I don't mean for you to have to spend your Saturday copying passages out of this (great reference, thanks!) book. I'll go track it down and add it to our library....
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