system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5, why does clay harden when heated instead of melting?
gpt
Clay that can be easily sculpted is a bunch of extremely small rock/earth particles mixed with some water. The layer of water between all the particles helps them stick together even when you push and sculpt them. When a clay object dries out, you end up with particles which are just resting in a big pile without any water to hold them together, which is why air dried clay is really easy to break - there's nothing holding the particles together. During the firing process in a kiln, all the little particles in the clay fuse together (the easiest way to picture this is a bunch of spheres melting just a bit on their outer surface and then all those molten surfaces  sticking together).