White gold is an alloy of gold and combines pure gold with other white metals, such as zinc, nickel, platinum, palladium, copper, manganese and silver. Durable and resistant to tarnish, white gold is brittle and requires platinum or rhodium plating. Generally produced to be a more cost effective than platinum, white gold can cause allergic reactions once the plating wears off.
White gold is a popular alternative to yellow gold, silver or platinum. Some people prefer the silver color of white gold to the yellow color of normal gold. The karat weight system used in white gold is the same as that used in yellow gold. 18K yellow gold and 18K white gold contain the same proportion of gold; only the remaining 25% of the alloy is different.
The properties of white gold depend on its composition. The white color is from the rhodium metal plating that is applied.
White gold is made from a gold-palladium-silver alloy or gold-nickel-copper-zinc alloy. One in eight people experience a reaction to the nickel containing alloy, usually in the form of a skin rash. A recent E.U. directive has indicated that soon all jewelry will have to be nickel safe with only a few ppms being allowable.
The white gold (18K) typical compositions:
-Gold 75%, Platinum or Palladium 25%
-Gold 75%, Silver 4%, Copper 4%, Palladium 17%
-Gold 75%, Palladium 10%, Nickel 10%, Zinc 5%
-Gold 75%, Copper 5.5%, Nickel 14.5%, Zinc 5%
The white gold (14K) typical compositions:
-Gold 58.5%, Silver 0.5%, Copper 27%, Nickel 7%, Palladium 7%
-Gold 59%, Copper 25.5%, Nickel 12.3%, 3.2% Zinc.
The white gold (9K) typical composition:
-Gold 37.8%, Copper 40%, Zinc 10.4%, Nickel 11.8%
Alloying produces a difference in the atomic structure which alters the reflectivity of light of different wavelengths.
White gold was developed to give a different look to jewelry. The white color is very fashionable for wedding rings, and when used side by side with yellow gold, it creates a striking effect.
White gold has been fashionable in jewelry as a more affordable alternative to platinum. This trend is evident in art deco jewelry.
Palladium is a metal which is ideal as a constituent of white gold. The disadvantage is the high melting point, although jewelry manufacturing and repair equipment has improved, so that most workshops can now cope.
Additions of about 10 -12% palladium to gold impart a good white color. But palladium is an expensive metal and it is also a heavy metal. Thus jewelry with palladium white gold will be more expensive than identical pieces in nickel whites. It is also more difficult to process as the melting temperatures are substantially higher.
Many commercial palladium white gold only contain about 6-8% palladium plus silver, zinc and copper. Some contain some nickel. These may also have less than a good white color and so are rhodium plated.
Other possible whiteners include silver, platinum, chromium, cobalt, tin, zinc, and indium. Silver would be an ideal constituent, with excellent working properties, but unfortunately it does not have a very great bleaching effect. Copper does not tend to whiten, but is used to improve the ductility of most white gold alloys.
In the European Union, there is a demand for cheaper alternatives to white gold than the palladium whites which are nickel free. Many new alloys are coming to market, most of which rely on manganese additions as whitener. Chromium and iron are also be used as whiteners. They tend to be hard and more difficult to process. Many of these alloys are not a good white color, requiring rhodium plating, and many suffer cracking problems and tarnishing.
Examples of white gold jewelry:
18K white gold ring
14K white gold ring
9K white gold ring
I will continue the explanations for each metal. Next post Rose gold.
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