Knowledge of the relevant mechanical properties of carat golds in the elastic region can help good design and extend the useful life of gold jewellery. Mechanical properties in the plastic or permanent deformation region determine manufacturing processes and their limits. Data published for carat-gold alloys are adequate for most design and process planning purposes. Critical application of engineering design principles requires more care because data from different sources are not always strictly comparable. The main reason for this is that most expensive alloys are tested using small specimens that simulate the scale on which jewellery is made but it does increase the risk of errors due to local segregation and small defects. The characteristics of the test machine can also be more intrusive than would be the case for large scale testing. This paper describes relevant mechanical properties and the various ways they are measured. The properties are related either to design or to processes used in the manufacture of gold jewellery. Examples include setting prongs/claws, finger rings, brooch clasps, complex raising, swivel rings and related chain-making. Most jewellery designs need careful selection of appropriate gold caratages and alloy condition. Some over-ambitious jewellery processes can create potential defects that later result in premature failure of a piece of jewellery and great difficulties in adjustment or repair. A good understanding of mechanical properties helps in reaching an optimum design solution that is often a calculated compromise between high strength and high ductility.

Author: Dr. John C. Wright