Most metals, such as copper, bronze, gold and silver, are soft enough to be worked whilst cold. Operations such as hammering and beating (including repoussé and chasing), cutting and engraving could be carried out without any heating to make the metal softer. Iron and steel, by contrast, have to be heated before they can be shaped (see forging). Most of the softer metals, however, cannot be cold worked indefinitely. With continous working, the metal becomes brittle and eventually fractures. This has to be counteracted by periodic gentle heating of the metal, called annealing. If the annealing is carried out correctly, it allows crystals within the metal to recrystallize and so distribute the stress that has built up. Cold working can then go on until the metal becomes brittle again. Metallographic examination, by study of the crystal structure, can yield information about the cold working and annealing processes in the last stages of making an artefact. Pure gold is one of the few metals that can be cold worked indefinitely without annealing.
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983Copied