Lapping is a form of grinding, in which a mixture of oil and grinding grit – generally corundum in powder form – is applied to a plate (most often made of cast steel). The surface of the work piece to be lapped is moved in circular movements on the plate. When this is done, the grinding grit is imbedded in the soft forged steel and produces a grinding removal of material on the work piece. Lapping is used mainly for machining hard work pieces made of steel, hard metal or ceramic where dimensional and form tolerances of mere micrometers are required. Other areas of application are found in the optics industry for working optical glasses, quartz, vitreous ceramics and wafers.