Blue Gold

Blue gold can be produced in a number of distinct colour ranges:

Clear blue gold - is produced when gold and Indium are alloyed together. This forms a gold inter-metallic compound. Gold with indium forms a compound with the chemical formula AuIn2. AuIn2 (46% gold content) which equates to approximately 12k purity grade. This gold-indium alloy has some workability and toughness.
Bluish hued gold - is produced when gold and gallium are alloyed together. This forms a gold inter-metallic compound. Gold with gallium forms a compound with the chemical formula AuGa2.. AuGa2 (58.5% gold content) which equates nicely with 14k (carat, karat) purity grade and would be hallmarked as such. This gold-gallium alloy has some workability and toughness.
Rich sapphire blue patina - can be produced on gold alloys by oxidation treatments. A 20 -23 carat gold alloy turns a rich sapphire blue when alloyed with ruthenium, rhodium and other metals and heat-treated to 1800°C.
Blue - an 18 ct gold with 24.4% iron and 0.6% maximum nickel forms a blue oxide layer when heated at 450- 600°C.
Blue-green - a 20 ct gold with 16.4% iron and 0.6% maximum nickel produces a blue-green colour when heat-treated to the same temperature.
This blue gold inter-metallic compounds are relatively brittle.

For more on gold alloys see Gold Alloy by Humagaia.

Making Blue Gold :: Production Processes
There are a number of processes that can produce blue gold.

Diffusion Bonding - partial surfaces may be strengthened with pure gold, silver or platinum or alloys thereof. Ornamental blue gold alloys are produced bythis method.
Electroplating and Annealing - layers of gold and indium can be electroplated onto a carat gold alloy. Annealing is then undertaken,
Surface Cladding - a jewellery welding laser is used to fill machined grooves with a thick blue gold surface cladding.
Liquid Metal Dip-coating - the dipping of jewellery pieces into liquid gallium or indium appears to be a simple, repeatable technique, due to the low melting points of these elements.

Blue Gold in Jewellery
The jewellery trade does not seem to have taken up the use blue gold intermetallic compounds in any quantity. This may be because the blue colour hues are a very pale colour. They are also relatively soft. This softness then leads on to the blue compounds being less hardy and they tend easily to abrade and scratch.

Blue layers can be obtained by oxidation of carat golds if additional elements are included in the blue metallic compound.

Blue Gold as a Product :: Blue Gold in Jewellery
The conventional jewellery application of blue gold is in the form of cast and ground items, which are set similar to gemstones. Due to the inherent brittleness, the setting has to provide enough strength, keeping mechanical stress away from the blue parts.

Blue gold, AuIn2 has the highest corrosion resistance and does not show any colour changes. Direct contact of blue gold jewellery with skin, should be avoided.

Cast pieces of blue gold alloy can be machined or faceted by grinding or milling. This produces blue gold that can be set in conventional gold jewellery.

Several companies have launched ranges of jewellery with the blue intermatallic compond incorporated:

VA Blue Gold SA of Geneva, Switzerland (subsequently liquidated in 1996)
Steven Kretchmer, died 2006
Jarretiere, of Italy
You can see to the right a piece of mixed colour blue gold jewellery that has been produced using this method. As you can see it is a stunning examples of the art and craft of jewellery manufacture enhanced with moderated blue colouring of the inset blue gold.

The first azure gold intermetallic products were presented in 1994. In 1995 some were presented at the Jewellery Fair in Warsaw, Poland.

There are stunning pieces of blue gold jewellery to be found, if you look in the right places. If you look hard enough you will be able to include a blue gold piece of jewellery in your collection and brag about it when you next wear that complimentary dress. "Where did you get that?", I hear them say, "Ah, that is my little secret", comes the reply.

Blue gold - priceless!