An alloy of gold and tin is used to produce jewelry that is very strong and resistant to scratches and dents. It also has excellent wear resistance and lustre. The metallurgist chooses the proportions of metals in an alloy to optimize specific properties of the product it is being used for such as conductivity, workability and strength. Alloys are often more cost-effective than pure metals and offer a better balance of properties, such as corrosion resistance, cost, and machinability.
Alloys of gold with copper and silver are very common in the jewellery industry, particularly green gold (gold 25 per cent, silver 75) and dead-leaf gold (gold 70, silver 40). These have a distinct’metallic’ ring and can be used to make fine rings. When an alloy of gold is coloured, it is usually coated with a thin layer of tin or zinc to reduce its sensitivity to oxidation, which makes the coating more durable and resistant.
In alloys of gold with refractory elements, such as iron and cobalt, there is marked segregation on solidification. This results in a black coating known as black gold. The coating can be buffed off and a new coating applied to restore the original colour.
A newer alloy being gaining popularity amongst jewelers is all but pure gold plated with 1% titanium. This provides the golden luster of 750 gold with added durability. This material is commonly used to manufacture wedding bands and can be made in virtually any size or shape.