Plastic optics are often mass produced by injection, compression or injection-compression molding. Optical quality molds can be directly machined in appropriate materials (tool steels, electroless nickel, aluminum, etc.), but much greater cost efficiency can be achieved with electroformed mold inserts. Traditionally, electroforming of optical quality mold inserts has been carried out in nickel, a material much softer than tool steels which, when hardened to 45-50 HRc usually exhibit high wear resistance and long service life (hundreds of thousands of impressions per mold). Because of their low hardness (<20 FIRc), nickel molds can produce only tens of thousands of parts before they are scrapped due to wear or accidental damage. This drawback prevented their wider usage in general plastic and optical mold making.