brass, alloy having copper (55%–90%) and zinc (10%–45%) as its essential components. The properties of brass vary with the proportion of copper and zinc and with the addition of small amounts of other elements, such as aluminum, lead, tin, or nickel. In general brass can be forged or hammered into various shapes, rolled into thin sheets, drawn into wires, and machined and cast. Its ductility reaches a maximum with about 30% zinc and its tensile strength with 45%—although this property varies greatly with the mechanical and heat treatment of the alloy. Cartridge brass (70% copper, 30% zinc) is used for cartridge cases, plumbing and lighting fixtures, rivets, screws, and springs. Aluminum brass (not exceeding 3% aluminum) has greater resistance to corrosion than ordinary brass. Brass containing tin (not exceeding 2%) is less liable to corrosion in seawater; it is sometimes called naval brass and is used in naval construction. Dutch metal (80%–85% copper, 15%–20% zinc) is used as a substitute for gold leaf. When iron is added to brass it produces hard, tough alloys. One of these is delta metal (55% copper, 41% zinc, 1%–3% iron, and fractional percentages of tin and manganese), which can be forged, rolled, or cast and is used for bearings, valves, and ship propellers.