How and Why is Gold Alloyed ?

How and Why is Gold Alloyed ?

A number of elements are added to gold to change its properties. Here is a list of the most commonly used ones:

Silver: Acts to harden gold in conjunction with added copper. Also whitens its colour
Copper: Reddens gold and hardens it, especially when present with silver.
Zinc: Significantly lowers the melting point of alloys and consequently most solders contain zinc. Acts as a secondary whitener.
Palladium: Primary whitener of gold, especially in 18ct alloys. Raises the melting point.
Nickel: Another primary whitener which also makes for an inherently harder material. Usage more restricted due to the Nickel Directive.
Silicon: Has a de-oxidant effect during casting but can cause other problems

Thank you to Cookson http://portal.knowledgebase.net/display/2/articleDirect/index.asp?aid=232667&r=0.9207117