When making pottery, you’re ususally trying to avoid cracks. But there is a decoration technique where cracks are desirable, and that’s crackle glaze.
To achieve this effect, you use a glaze that shrinks faster than the clay when fired. This creates tension, which leads to cracks. Depending on the type of glaze, the type of clay and the firing temperature, you get big or small cracks.
Beware: this technique is not suitable for pots that need to be functional. Not only do the cracks in the glaze make the pot more fragile than other types of pottery, and the cracks can also become home to all kinds of bacteria. So only use this technique for decorative pieces!