burnish

Burnishing is a form of pottery treatment in which the surface of the pot is polished, using a hard smooth surface such as a wooden or bone spatula, smooth stones, plastic, or even glass bulbs, while it still is in a leathery 'green' state, i.e., before firing. After firing, the surface is extremely shiny. Often the whole outer surface of the pot is thus decorated, but in certain ceramic traditions there is 'pattern burnishing' where the outside and, in the case of open bowls, the inside, are decorated with burnished patterns in which some areas are left matte.