[somat]

Pyrex was one of the great customer betrayals. Corning built the brand to promote a specific blend of glass with it's specific properties. Successfully enough that that blend, borosilcate glass became synonymous with the brand, Pyrex. Breaking this link to ride on the coattails of trust the brand had while selling a different blend with different properties was a dirty move.

An interesting subject is how to differentiate borosilicate glass from tempered glass, It turns out to be surprisingly tricky, at least in a home kitchen setting. You could break it, easy but now you are can't use the dish. Color(blueish vs more clear) turns out to be a unfaithful test. There are ways to check the index of refraction(IOR) with oil, but it turns out the IOR of borosilicate and soda-lime overlap. I suspect the polarized light test to identify tempered glass stress would work, but that requires getting the polorizing filters and knowing what to look for. I sort of wish there was a requirement to stamp the formula right into the glass.