Colored gold

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Red gold redirects here. For the tomato processing company, see Red Gold.
Ternary plot of different colors of Ag-Au-Cu alloys

Pure gold is yellow in color, but colored gold in various other colors can be produced.

Colored golds can be classified to three groups:[1]

  • Surface treatments such as oxide layers



White gold[edit]

Rhodium-plated white gold wedding ring
For other uses, see White Gold (disambiguation).



A common white gold formulation consists of 90 wt.% gold and 10 wt.% nickel.[2] Copper can be added to increase malleability.[1]

The strength of gold-nickel-copper alloys is caused by formation of two phases, a gold-rich Au-Cu, and a nickel-rich Ni-Cu, and the resulting hardening of the material.[1]

The alloys used in jewelry industry are gold-palladium-silver and gold-nickel-copper-zinc. Palladium and nickel act as primary bleaching agents for gold; zinc acts as a secondary bleaching agent to attenuate the color of copper.

The nickel used in some white gold alloys can cause an allergic reaction when worn over long periods (also notably on some wrist-watch casings).[3] This reaction, typically a minor skin rash, occurs in about one out of eight people and because of this, many countries do not use nickel in their white gold formulations.

Rose, red, and pink gold[edit]


Rose gold is a gold and copper alloy widely used for specialized jewelry. Rose gold, also known as pink gold and red gold, was popular in Russia at the beginning of the nineteenth century, and was also known as Russian gold, although this term is now obsolete. Rose gold jewelry is becoming more popular in the 21st century and is commonly used for wedding rings, bracelets, and other jewelry.

Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content – the higher the copper content, the stronger the red coloration. Pink gold uses the least amount of copper content, followed by rose gold, and red gold has the highest copper content. Examples of the common alloys for 18K rose gold, 18K red gold, and 18K pink gold:

18K Red gold: 75% gold, 25% copper



12K Red gold: 50% gold and 50% copper.[2]



Rose gold[edit]

See also: Crown gold





The alloy of 76% gold, 19% copper, and 5% aluminium yields a yellow color, the alloy of 76% gold, 18% copper and 6% aluminium is pink.[1]

Green gold[edit]

Further information: Electrum

Green gold was known to Lydians as long ago as 860 BC under the name electrum, a naturally-occurring alloy of silver and gold.[2] It actually appears as a greenish-yellow rather than green. Eighteen karat green gold would therefore contain a mix of 75% gold and 25% silver (or 73% gold and 27% silver). Fired enamels adhere better to these alloys.

Cadmium can also be added to gold alloys but there are health concerns regarding its use.[5] The alloy of 75% gold, 23% copper, and 2% cadmium yields light-green 18-karat gold. The alloy of 75% gold, 15% silver, 6% copper, and 4% cadmium yields a dark-green alloy,

Grey gold[edit]

Grey gold alloys are made by adding silver, manganese and copper in specific ratios to the gold.[6]


All the AuX2 intermetallics have crystal structure of CaF2 and therefore are brittle.[1] Deviation from the stoichiometry results in loss of color. Slightly nonstoichiometric compositions are however used, to achieve a fine-grained two- or three-phase microstructure with reduced brittleness. A small amount of palladium, copper or silver can be added to achieve a less brittle microstructure.[7]


Purple Gold[edit]

Gold-aluminium phase diagram


Blue gold[edit]

Blue gold is an alloy of gold and indium.[9] It contains 46% gold (about 12 karat) and 54% indium,[2] forming an intermetallic compound AuIn2. While several sources remark this intermetallic to have "a clear blue color",[1] in fact the effect is slight: AuIn2 has CIE LAB color coordinates of 79, -3.7, -4.2[10] which appears roughly as a greyish color. With gallium, gold forms an intermetallic AuGa2 (58.5% Au, 14ct) which has slighter bluish hue. The melting point of AuIn2 is 541 °C, for AuGa2 it is 492 °C. AuIn2 is less brittle than AuGa2, which itself is less brittle than AuAl2.[7]


Surface treatments[edit]

Black gold[edit]

For the colloquial term black gold, see crude oil.





Blue gold[edit]


A rich sapphire blue colored gold of 20-23K can also be obtained by alloying with ruthenium, rhodium and three other elements and heat-treating at 1800 °C, to form the 3–6 micrometers thick colored surface oxide layer.[1]

See also[edit]


External links[edit]