Purple Gold :: Amethyst Gold :: Violet Gold :: Purple Gold Alloy :: Gold-Aluminum Purple :: Gold-Aluminum Purple

Purple gold is produced when gold and aluminium are alloyed together in the ratio 79:21 by weight. In this ratio they form a gold inter-metallic compound with the chemical formula AuAl₂. The gold alloy formed has a purple, amethyst or violet colour. This purple gold alloy can be hallmarked as 18k gold (carat , karat).

This purple gold inter-metallic compound is very brittle. At lower aluminium percentages, the alloy is less brittle but the colour is less defined . It cannot be worked by conventional metal working processes. It can be used similarly to enamel in infill.

It has been noted that silver additions to AuAl₂ shifted the colour towards yellow and presumably other additions may have a different effect.

Gold and aluminium powders thermal-sprayed onto a substrate have also achieved a purple coating.

For more on gold alloys see Gold Alloy by Humagaia.

There are a number of processes that can produce purple gold.

• Vacuum Melting - specialist equipment is required to alloy gold and aluminium together at a temperature of 1060°C.
• Physical Vapour Deposition (PVD) - in this process gold and aluminium are deposited, together, onto a gold substrate. Such processing can be done by a number of PVD techniques such as sputtering. Jewellery made by this approach is commercially available.
• Powder Metallurgy - additions of 7-30% cobalt, nickel or palladium powders added to the gold-aluminium powder can form purple gold. The resultant purple gold compound can be pressed and sintered.
• Vacuum Melting - atomising an ingot of gold-aluminium alloy and packing the powder into a mould and using an electrical discharge sintering process on the resultant.
• Diffusion Bonding - partial surfaces may be strengthened with pure gold, silver or platinum or alloys thereof. Ornamental purple gold alloys containing 70-85% gold with the remainder aluminium have been produced using this method.
• Thermal Diffusion - using bundles of gold-plated aluminium and aluminium-plated gold wires and drawing them down to produce a composite purple gold wire, then subject the wire to thermal diffusion treatment at 450-700°C in a reducing atmosphere. A wire with a fibrous structure of purple gold is produced that is tough and flexible.
• Thermal Diffusion in Jewellery (Jewelry) - thermal diffusion can be used to introduce a purple gold effect on gold jewellery by depositing a layer of aluminium onto the surface and undertaking thermal diffusion to form the purple gold compound.
• Thermal Spraying - gold and aluminium powders are sprayed onto a substrate achieve a purple coating.
• Mix Gold Chloride with Rochelle Salt - mix dilute gold chloride solution (0.01%) with 1% potassium sodium tartrate (Rochelle salt) solution to produce a purple gold aluminium compound.

Highly stable purple gold can be melted and cast into a mould.

The conventional jewellery application of purple gold is in 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 purple parts.

Direct contact of purple gold jewellery with skin, should be avoided.

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

You can see to the right a selection of purple gold jewellery that has been produced using this method. As you can see they are all stunning examples of the art and craft of jewellery manufacture enhanced with moderated purple colouring of the inset purple gold.

To date I have seen very few examples of this colour of gold jewellery, but if you are in love with the colour purple, amethyst or violet then this coloured jewellery is your 'must have' when next hubby needs to curry favour for your affections.

Ladies, I give you purple gold, amethyst gold or violet gold!

For more coloured golds see Gold Colours :: Gold Colors by Humagaia.

For the next in this series of gold colours see Gold :: Blue Gold by Humagaia

For the previous in this series see Gold :: White Gold by Humagaia

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