Gold-Silver-Copper :: Au-Ag-Cu :: Common Gold Alloy Metals :: What Alloy Elements in Yellow Gold

While pure gold is yellow in colour, coloured gold can be developed into various hues by the process of alloying gold with other elements (usually metallic) in varying proportions. It is usual for gold to be mixed with other metals to produce an alloy, simply a mixture of two or more metals.

Throughout history, most people have preferred the colour of gold jewellery to remain close to that of pure gold itself, and so most jewellery has been made using yellow gold alloys. 

There are hundreds, if not thousands, of possible alloy combinations, compositions and mixtures. In general there are 2 main metal elements that influence the colour of gold alloys:

• silver - colours gold white,
• copper - will colour gold red.

Most gold alloys are a mixture of gold, copper and silver. These three metals have a great metallurgical affinity for each other.

Small amounts of other materials (usually metallic) are also added to provide special characteristics. Other metals that are inclusions in gold metal alloys and influence the colour variations of gold alloys include:

• Aluminium (Aluminum) (Al) - produces purple gold when in combination with gold in ratio 80wt% gold and 20wt% aluminium; yellow coloured gold when in ratio 76wt% gold, 19wt% copper and 5wt% aluminium; with a slight variation in the copper : aluminium ratio to 18wt% : 6wt% the colour changes to pink.
  
  See Gold Aluminium :: Gold Aluminum by Humagaia for further details on gold intermetallic compounds.
• Nickel (Ni) - whitens in combination with other metals. 75wt% gold with 25wt% nickel gives nickel white alloy.
   See Nickel Gold by Humagaia
  
  Nickel can have an allergic reaction for 20% of the population. Rhodium plating may be necessary.
  See White Gold :: Nickel Allergy by Humagaia.
• Indium (In) - produces a clear blue gold intermetallic.
• Zinc (Zn) - additions of up to 15wt% can be added to alloys of the Au-Ag-Cu system to change the red colour of copper-rich alloys to reddish yellow or dark yellow.
• Platinum (Pt) - produces white gold and is used as a whitener in white gold production.
• Palladium (Pa) - produces white gold. 75wt% gold with 25wt% palladium gives palladium white gold.
  See Palladium Gold by Humagaia
• Iron (Fe) - used as a substitute for palladium in the manufacture of white gold. Produces grey-white gold in combination with copper; blue-white or blue gold in combination with gold alone in 75wt% gold and 25wt% iron. Rhodium plating may be necessary.
• Gallium (Ga) - produces gold intermetallic with a bluish hue.
• Ruthenium (Ru) - used in some blue gold intermetallic compounds
• Rhodium (Rh) - also used in some blue gold intermetallic compounds
• Cobalt (Co) - used in some black gold intermetallic compounds
• Iridium (Ir) - an additive in small quantities in green gold alloys.
• Manganese (Mn) - used as a substitute for palladium as a whitener or 'bleaching' metal to give white gold. Rhodium plating may be necessary.
• Chromium (Cr)- also used as a substitute for palladium as a whitener or 'bleaching' metal to give white gold. Rhodium plating may be necessary.
• Titanium (Ti) - assists iron and copper in producing a black gold intermetallic compound.
• Cadmium (Cd) - additions of up to 4wt% have also been used for the production of 18 carat green alloys:75wt% gold, 23wt% copper and 2wt% cadmium results in a light green gold alloy; 75wt% gold, 15wt% silver, 6wt% copper and 4wt% cadmium results in a dark green gold alloy (20). Cadmium oxide (CdO) is very toxic, being an irritant to the respiratory system, causing irreversible damage to the kidney.

Nickel, zinc, and palladium are common constituents of white gold alloys.

Various colourful tones of gold are displayed when precious metal alloys are blended with pure gold. The various gold tones include:

Yellow gold - produced by blending gold with silver and copper. Alternatively, an alloy mixture of 76% gold, 19% copper, and 5% aluminum yields a yellow gold alloy colour.
See Gold :: Yellow Gold by Humagaia for further exploration of this coloured gold alloy combination.

Green gold - additions of silver make the gold alloy greenish.
See Gold :: Green Gold by Humagaia for further exploration of this coloured gold alloy combination.

• White gold - is created by increasing the silver-coloured alloys (zinc, silver, nickel), but most often contains a large proportion of silver. White gold jewellery is the most popular and most often referred to after yellow gold. White gold first came into vogue in the 1920's. White gold is made by adding "white" metals such as platinum, silver, zinc and nickel to gold.
  See Gold :: White Gold by Humagaia for further exploration of this coloured gold alloy combination.

• Rose gold - (aka red gold or pink gold) created by blending of copper with a smaller percentage (by weight) of silver or aluminium, for instance an alloy mixture of 76% gold, 18% copper and 6% aluminium yields a pink gold alloy colour.
  See Rose Gold, Red Gold and Pink Gold Alloys by Humagaia for further exploration of these coloured gold alloy combinations.

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