Burnishing is polishing leather-hard or bone-dry clay with a smooth, hard tool such as a stone, spoon or the back of a ladle, so the surface particles line up and the fired piece has a soft sheen without any glaze.
What Is Burnishing?
Burnishing is one of the oldest ways of finishing pottery. Rubbing the clay compresses the surface and lays the fine platelets of clay flat, so the surface reflects light. It works best on fine clays and is often done over a coat of terra sigillata, which is made of only the finest particles.
Timing matters. Most potters burnish at the leather-hard stage, sometimes going over the piece several times as it dries. Burnishing too early smears the clay, and too late can scratch it.
The shine survives best at low firing temperatures. Fired too hot, the clay shrinks and the polish fades, which is why burnished work is usually bisque fired low and often finished with pit, saggar or smoke firing. Burnished surfaces aren’t watertight, so they suit decorative pieces rather than tableware. A little wax or polish rubbed on after firing deepens the sheen and makes the surface easier to keep clean.
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.