Red Gold is copper and gold mixed. The higher the copper concentration, the redder the gold is.
Blue gold is a mix of gold and indium.
There are different methods to making black gold
Wikipedia to the rescue!
“Black-colored 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.
- Patination by applying sulfur– and oxygen-containing compounds.
- Plasma-assisted chemical-vapor deposition process involving amorphous carbon
- Controlled oxidation of gold containing chromium or cobalt (e.g. 75% gold, 25% cobalt).
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