White gold
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White gold is an alloy of gold and at least one white metal, usually nickel or palladium.<ref>Template:Cite web</ref> Like yellow gold, the purity of white gold is given in carats (karats). It is often used on jewellery.<ref>Template:Cite book</ref>
A common white gold formulation consists of 90% wt. gold and 10% wt. nickel.<ref>Template:Cite book</ref> Copper can be added to increase malleability.<ref name="cretu"/>
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 karat, 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.<ref name=cretu>Template:Cite journal</ref>
While some higher-quality white gold alloys retain their shine and lustre, most will be coated with a very thin layer of rhodium. This gives the naturally more-dull white gold a shine comparable to platinum or silver; however the rhodium may wear off over time.<ref>Template:Cite web</ref>
Skin irritation
The nickel used in some white gold alloys can cause an allergic reaction when worn over long periods (also notably on some wristwatch casings).<ref>Template:Cite web</ref> This reaction, typically a minor skin rash from nickel dermatitis, occurs in about one out of eight people; because of this, many countries do not use nickel in their white gold formulations.
White gold alloys made without nickel are less likely to be allergenic.<ref>Template:Cite web</ref>