The Metallurgy of Gold

Abstract

The discovery of gold about 7000 years ago together with that of its sister metals from group IB of the periodic table can be said to have laid the early foundations of metallurgy as a science and a technology. The attraction of the metal to man derives from its relative scarcity and high value, its excellent corrosion resistance, its unique yellow colour and the fact that it is one of the most malleable of all metals. The metallurgy of gold is discussed with reference to its physical and mechanical properties, its fabrication and alloying behaviour and electrodeposition processes. Those properties which are particularly relevant to the use of gold in various applications are highlighted. The reasons for the yellow colour and the effect of alloying on colour are given. The malleability of gold allows it to be hammered to extreme thinness and the production of gold leaf is described. Solid solution and compound formation in alloys of gold are considered in terms of the alloying theory of Hume-Rothery, Raynor and their coworkers, and particular mention is made of gold–mercury amalgams and their use in the 'fire gilding' process for producing gold coatings on other metal substrates. This process was rendered obsolete by the development of electroplating. The principles and practice of gold electroplating and electroforming are discussed.