Gold is unique amongst the precious metals in that conventional karat gold jewelry can be produced in a range of colors from red to several shades of yellow, green and white, simply by varying the ratios of the alloying metals. More interestingly, it is also possible to produce karat gold jewelry in special colors such as purple, black and blue. Some of these exotic colors are obtained by alloying gold with certain other metals at fixed compositions to produce special structures known as intermetallic compounds. Atypically for gold alloys, such intermetallic structures are intrinsically brittle; they are not malleable and cannot be fabricated into complex shapes by conventional working techniques. The other colors are obtained by forming surface oxides or patinas similar to those used to color cast bronze sculptures. What is the technical basis for producing such unusual colors? What are intermetallic compounds? How are surface oxides or patinas produced on gold? How can jewelry be produced using their unique colors? Can such approaches be used for other precious metals such as platinum? The answers to these questions will be examined in this presentation. Some thoughts on the possibility of new colors will also be considered. For example, ternary intermetallic compounds or use of a gold nanotechnology approach may provide some novel enamel colors.

Author: Dr. Christopher W. Corti