Pieces of metal cast with plane facets in the form of crystals. They reflect the light so as to have a dark luster. The alloy of which they are made is composed of tin 29, lead 19. This alloy when melted will adhere to the polished surfaces with which it is in contact and leave them on cooling. The thickness of the deposit is regulated at will by the time of contact. It is also used for making metallic mirrors.