Hardening is due to the
precipitation of second phases and ordering reactions in the crystal structure.
The ‘990’ gold – one per cent titanium alloy – is also age hardenable.
The term heat treatment
can be applied to the annealing of cold
worked alloys which softens and restores ductility to the alloy.
Heat Treatment
Many copper-containing carat
golds of 18 and lower caratages are amenable to an ‘ageing’ heat treatment, typically
at temperatures of about 300 degrees centigrade, which confers considerable hardening
to the alloy, resulting in improved wear and scratch
resistance of jewellery.