Agateware is pottery made from two or more differently coloured clays layered, folded or marbled together, so the swirled pattern runs right through the clay rather than sitting on the surface like a glaze or slip.
What Is Agateware?
The name comes from the banded stone agate, which the swirling patterns resemble. Potters make it by stacking slabs of coloured clay, cutting and recombining them, or by lightly wedging two clays together and throwing the result. The related Japanese technique of building patterns from coloured clay slabs is called nerikomi.
The colours usually come from stains or oxides added to one base clay, which is the safest approach. Mixing two different clay bodies can cause cracks along the joins, because different clays shrink by different amounts as they dry and fire. Using one body for every colour avoids most of that trouble.
Throwing agateware smears the pattern, so many potters scrape or trim the surface at leather hard to reveal crisp lines. It is often finished with a clear glaze, or left unglazed and polished on the outside, so the clay pattern stays the star of the piece. Keep a slice of each coloured clay as a test tile, because stains can shift colour quite a lot in the kiln.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.