White gold
White gold is an alloy of gold and at least one white metal, usually nickel or palladium. Like yellow gold, the purity of white gold is given in carats.
White gold's properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for different purposes; while a nickel alloy is hard and strong, and therefore good for rings and pins; gold-palladium alloys are soft, pliable and good for white gold gemstone settings.
The highest quality white gold is usually at least 18 carat, and made up of gold and palladium, sometimes with other metals like copper, silver, and platinum for weight and durability, although this often requires specialized goldsmiths.
Making gold white
Making gold white is similar to mixing colours in paints. Adding a red metal (copper) will tend to make gold red and adding a white metal tends to make gold paler and eventually white. Thus, all other alloying metals to gold, apart from copper, will tend to whiten the colour and so it is possible to make carat gold’s that are a reasonable white colour.
Whilst additions of any white metal to gold will tend to bleach its colour, in practice, nickel and palladium (and platinum) are strong 'bleachers ' of gold, silver and zinc are moderate bleachers and all others are moderate to weak in effect.
This has given rise, historically, to 2 basic classes of white gold’s - the Nickel whites and the Palladium whites.
The nickel-whites tend to have a colder white colour, whereas the palladium whites have a warmer colour. Good nickel whites tend to be hard and difficult to process. Good palladium whites tend to be soft, easy to process (but lost wax casting is more difficult) but are much more expensive, because of the price of palladium.
Consequently, many commercial white alloys are thrifted in nickel or palladium and contain some copper; hence, colour is compromised.
At the 8-10 carat (33.3 - 41.6% gold) level, gold-silver alloys are quite white, ductile although soft and are used for jewellery purposes.
Contact allergy
About one person in eight has a mild allergic reaction to the nickel in some white gold alloys when worn over long periods of time.
A typical reaction is a minor skin rash. White gold alloys made without nickel are less likely to be allergenic.
The hallmarks are the same for any gold
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