Bonnie Rubinstein wrote:Why would Spectrum and Oceanside not be compatible? I assumed they were using all the same technology and formulas.
Similar (not necessarily same) technology and formulas, but different manufacturing facilities, different countries, different levels of experience. It's really hard to make consistently compatible glass. Each manufacturer tests vs the product they're making, but almost no one tests vs products from other manufacturers (past or present).
can you elaborate on 'more to it than coefficient compatibility? That is really disconcerting!
In most cases, the laboratory test for measuring coefficient of expansion measures the difference in expansion between room temperature and 300C/572F. That's fine, EXCEPT that we fuse glass at a much higher temperature, one well out of the range of that measurement. The expansion above 300C/572F is at least as important (if not more important) than the expansion below that temperature. Expansion at higher temperatures can be several times greater than expansion at lower ones. And, to make things more difficult, it's not necessarily a linear relationship.
Add to that the fact that another factor -- viscosity, or the runniness of a glass at a particular temperature -- is also important in making compatible glass. It's possible to have two glasses with the same COE but different viscosities be incompatible. The glass manufacturer needs to take viscosity into account; it's the combination of the two factors that matters.
As an example, Bullseye clear 1101 has a COE of 91, while their white 0113 (which has a very different viscosity) has a COE of 88. Yet they're compatible because the manufacturer has taken steps to make sure they work together at FUSING temperatures, not in the range of the COE test.
The distributors I have spoken with seem to say the Wissmach and Oceanside are compatible)
Your experience proves that that's not always true.
As a general rule, I like to find a manufacturer I trust and depend on them to make sure the glass is compatible. If I use glass from another manufacturer, I always test first to make sure the two glasses are truly compatible.
