Gold jewelry comes in many colors, variants on the classic pure gold.
In recent years, thanks to new technologies, new gold jewelry colors have evolved. Gold jewelry can now be found in colors such as black gold, green gold, purple gold and blue gold. Colored golds are becoming more popular in their use in modern gold jewelry design.
These colors are generally obtained by alloying gold with other elements
in various proportions.
Colored gold can be classified to three groups:
1-The Au-Ag-Cu system, producing white, yellow, green and red gold.
2-The intermetallic compoun, producing blue and purple gold.
3-The surface oxide layers, such as black gold.
1.- Black gold can be produced by various methods:- Electroplating using black rhodium or ruthenium. Solutions that contain ruthenium give a slightly harder black coating than those that contain rhodium.
2.- Patination by applying sulfur and oxigen containing compounds.
3.-Plasma Assisted Chemical Vapor Deposition process. Amorphous carbon is used.
4.-Controlled oxidation of gold containing chromium or cobalt can also be made to yield black gold.
For black colored gold, the blacker the gold, the less wear resistant it would be.
14 K Black gold ring
Blue Gold is an alloy of gold and ferrous metals, resulting in gold with a bluish tinge.
18K Blue Gold, Gold 75%, Iron 25%
Blue Gold Is also made as an intermetallic compound between gold and indium. The gold derives a bluish hue color
12K Blue gold, Gold 46%, Indium 54%
With gallium, gold forms an intermetallic compound between gold and gallium.
12K Blue Gold, Gold 58.5%, Gallium 41.5%
14K Blue gold ring
The green gold is an alloy made with gold and other metals like silver, copper and cadmium.
The green color varies with the proportion of other metals:
18K Soft green gold, Gold 75%, Silver 25%
18K Light green gold, Gold 75%, Copper 23%, Cadmium 2%
18K Green gold, Gold 75%, Silver 20%, Copper 5%
18K Deep green gold, Gold 75%,Silver 15%, Copper 6%, Cadmium 4%
Cadmium is, however, highly toxic.
14 K green gold ring
Is also named amethyst or violet gold. The process to make purple gold is to alloy gold and aluminum or palladium in a certain fixed ratio. Gold content is 80% and is 18K gold. Tend to be a little brittle.
Purple gold is an intermetallic compound instead of a malleable alloy.
18K Purple gold, Gold 80%, Aluminum 20%.
Invented by a metallurgy professor at Singapore Polytechnic.
Purple gold acts like a gemstone adorning white gold rings and pendants.
18K Purple gold ring
I will continue the explanations for each metal. Next post silver.
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