The color of copper is dull red. In malleability and ductility, either hot or cold, it ranks very high. Its tensile strength is about 30,000 lbs., although rolling, hammering or drawing it into wire nearly doubles its strength. It fuses at about 1985° F. The most striking properties of copper are, (1) the adverse way in which the smallest amount of impurity affects it, and (2) its superior conductivity for heat and electricity when pure (99.9%).

It is easily forged or rolled hot or cold and when worked cold it becomes hard, as in wire drawing, but it may be again softened, or annealed, by heating to red heat and plunging into cold water, which also causes a loss of the tensile strength gained by working.

Commercial copper is often very impure, containing arsenic, antimony, copper oxide, iron, and lead, according to the ores from which extracted. This must be refined, and should then be 99.8% pure for high grade uses. Refineries supply copper for market in (1) "pigs" for melting and making alloys, (2) slabs for rolling into sheets for various uses, and (3) ingots for wire or tube-drawing.