Why Pyrex?

I baked a pie today in a pyrex glass baking dish. Have you ever wondered why Pyrex is bake-able when art glass is usually so fragile and easy to break? Even if you haven't wondered - heres the reason why! :)

Glass is hot and molten at temperatures well over a thousand degrees Fahrenheit. Thermal shock is a big threat to glass, more stressful than brute force, and every type of glass has a particular temperature that triggers the release of stress. This temperature range is called the "stress point" and for most art glass its around 150 degrees Fahrenheit. For Pyrex, the stress point is up around 950 degrees Fahrenheit - this is drastically higher, and this is why you can put Pyrex glass on a stove burner and heat it up without breaking the glass. If you did this with art glass the piece would certainly break. But with Pyrex, there is no way you are going to heat the glass up anywhere near 950 degrees Fahrenheit in the kitchen, so there is much less of a chance that you might break the glass.

Although if you take a hot Pyrex dish and throw it in the sink and run cold water over it, be careful, any introduction of stress will probably cause the glass to break (the thermal shock of getting hot than cold so fast is very stressful, even for Pyrex).

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