The chemistry behind it? I Googled, and didn’t find any good explanations.
Just wondering.
I thought it was because it’s already been baked in a very hot oven.
Because they’re made of clay, which can be molded when wet, and is dried and baked to make bricks, pottery, and ceramics. Here’s an interesting article about clay:
https://www.sciencelearn.org.nz/resources/1771-what-is-clay