When Pyrex cookware first came out, it was advertised as "icebox to oven." Because it was made of borosilicate glass, which could weather large temperature changes without undergoing thermal shock, and shattering. But today, American Pyrex and Anchor Hocking dishes are made of soda lime silicate glass, which is more prone to shatter. So says a report in the Bulletin of the American Ceramic Society. [R. C. Bradt and R. L. Martens, Shattering Glass Cookware]
Researchers calculated that a rapid temperature change of just 100 degrees Fahrenheit could fracture the new glass—compared to 330 degrees for the old stuff. They say that means it's possible to break a glass measuring cup with boiling water. Or to explode a cool casserole dish by sliding it into a hot oven.
Manufacturers say they temper the new glass to make it stronger. And researchers did find some evidence of that. But they believe that the heat treatment was inadequate. Because in lab tests, the cookware exploded into large glass shards, rather than tiny pieces, as tempered auto glass does.
As the saying goes, if you can't stand the heat, stay out of the kitchen. If this research is accurate, the heat is on this cookware.
[The above text is a transcript of this podcast.]