Gold Alloys:

Gold is alloyed with other metals usually to increase its hardness. Gold can be alloyed with silver in all different proportions, the strongest being 50% gold to 60% silver. Gold-silver alloys are easy to work with and can be harden at low temperatures. When more and more silver is added the color of the gold changes gradually from yellow to white. Green alloy can be created from a mixture of 75% gold to 25% silver. An addition of high percentages of silver results in dull white alloys that will tarnish easily.

Gold can also be alloyed with nickel which is most popularly used as the bases for white gold jewelry. The alloy contains 80% gold, 16% nickel 3% to 4% zinc and up to 1% copper. Zinc is used in low-karat alloys as a deoxidizer.
 
Gold alloyed with copper is widely used in coins. These alloys result in a red to pick color. The copper is added to harden the gold. Copper-gold alloys have a relatively low melting point. Gold, copper and silver alloys are very workable and used in goldware, while 90% gold mixed with 10% copper produces metal that is prone to cracking.

Gold alloyed with palladium is very easy to work with. The maximum hardness for these alloys occurs when 60% to 65% palladium is present. Gold-palladium alloys can be used for jewelry. Gold, palladium and iron are used in potentiometers because this alloy shows very high electrical resistance.

Different Colors of Gold:

Gold alloys, aside from strengthening gold for jewelry, can also affect its color. The following table demonstrates the most common colors of gold alloys and the metals used in making them:
 

Color of Gold	Additional Metals Used
Yellow Gold	Copper, Silver
White Gold	Nickel, Zinc, Copper
Green Gold	Silver, Zinc, Copper
Rose Gold	Copper, Silver