# Why doesn't stovetop glass crack from thermal shock?

I have a feeling that if my stovetop was made out of regular glass, it would have cracked from rapid cooling/heating a long time ago – especially if you consider accidental water spills. What kind of glass is able to withstand such abuse?

Stovetops are made of glass-ceramic which has extremely low thermal expansion, hence no cracking from temperature change. In fact, the coefficient is with $$0.1 \cdot 10^{-6} \ 1/K$$ even lower than that of Borosolicate glass at $$3.3 \cdot 10^{-6} \ 1/K$$. Since glass-ceramic can reach a negative coefficient of thermal expansion, getting even closer to zero is just a matter of engineering (thanks to @Volker Siegel for this interesting fact).

The brand name for one kind of glass-ceramic, Ceran (by German company Schott) is in German often used to generally describe glass-ceramic stovetops. Borosilicate glass is, to my knowledge, used only for heat-resistant cookware, but not the stovetops themselves.

• In principle, glass-ceramic can even reach a negative coefficient of expansion, so it is purely a question of engineering to get the coefficient of expansion to near zero. Aug 22 '20 at 3:25
• @Volker Siegel thats a pretty interesting fact, thanks! I added it to my answer if you don't mind Aug 22 '20 at 8:48

Borosilicate glasses (e.g. "Pyrex") have small coefficients of expansion (about $$3.3\times 10^{-6}$$/°C compared with $$10\times 10^{-6}$$/°C for steel) and can tolerate temperature differentials of about 180 °C or 330 °F.

It doesn’t crack because it is the so-called Pyrex glass. It is not the same glass as common window glass which is still silica, but blended with sodium and calcium. Pyrex is silica blended with boron, making it way more thermally stable because of a smaller thermal expansion.

It also exists as pure silica glass, used mostly in high end optical applications (microscopes, lab instruments, etc.) which is even more stable and can withstand temperature variations up to a thousand degrees.

• It is plausible to use this kind of glass, and it could work. I think it may not stay absolutely flat, depending on thickness. But, for this use case, the class is further tweaked to even lower. Note it does not need to be clear! (see other answer) Aug 22 '20 at 3:08
• The coefficient of thermal expansion is 5.5 ⋅ 10−7/K for pure silica (inbetween the two mentioned by OpticalResonator). Aug 23 '20 at 14:41