A luster is a metallic based decoration that has been used on ceramics since the 9th century. Lusters are metallic salts that are applied over already-fired glazes and then the ware is re-fired to cone 022 to cone 018. The lower firing temperature allows the luster to bond with the existing glaze. The result is an extremely thin layer of metal on the surface of the glaze. The fired luster is very fragile and easily scratched.They are characterized by their iridescent sheen and varying color shades of soft metallic-like hues. Lusters come in several forms, including liquids for brushing and pastes for screen printing.