Grades 3–5 · Materials & Matter
Why does firing turn a clay pot into a different material?
A wet clay pot can be reshaped. After it dries, it feels firmer, but drying is not the same as firing. A pot that has only dried still contains tiny mineral particles joined much less strongly than they will be after firing.
In the diagramA kiln does more than dry a clay potFiring changes the material and joins its tiny particlesUnfired clayFired ceramicTiny clay particlesStrong contacts developA fired pot does not turn back into soft clay when wet.
A kiln heats the shaped clay far beyond ordinary drying conditions. The material undergoes chemical and structural changes, and strong connections develop between particles. This joining is called sintering. In many clay bodies, some ingredients also form a glassy material that helps join the remaining particles as the pot cools.
The whole pot does not need to melt into a liquid. Instead, its tiny parts become connected in a new, stronger structure. A fired pot does not turn back into soft clay when water is added. Some fired ceramics still contain pores, so firing alone does not make every pot waterproof. Different clay mixtures and firing conditions produce different kinds of pottery.
About this explanation
Starting knowledge: Recognize that wet clay can be shaped and that drying removes water.
Sources
- University of New South Wales School of Materials Science and Engineering — Firing and sintering