A Technique for the Metallographic Examination of Gold Coatings Using an Electrodeposited Iron Support

Summary

Metallographic examination of thin metal coatings in microsection is facilitated by a supporting metal electrodeposit. The high corrosion resistance of gold requires aggressive etchants, and the usual supporting deposits of copper or nickel are undermined. The corrosion resistance of gold and iron can be reversed in cyanide solutions, and use has been made of this to devise a technique using iron wire substrates to study the structure of gold electrodeposits. Thick coatings can be plated using only a small amount of precious metal. Gold already plated on another substrate is overplated with iron, the original basis dissolved, and a second iron deposit applied. The structure of gold mounted in iron may be revealed either by chemical etching in cyanide-persulphate mixtures, or by anodic etching in alkali cyanide solution, in both of which iron is passive.