Burnishing is a finishing process used to improve the surface finish of a material by plastic deformation. It is typically achieved by compressing the material surface with a hard, smooth object. The object is often a hardened steel ball or roller that is rotated or slid over the material surface at high pressure. The pressure applied during burnishing causes cold-working of the material, which results in a hardened and polished surface. Burnishing can be used to improve the surface finish of many materials including metals, plastics, ceramics, and glass.