Gold is the softest metal element – too soft for most uses – so it is mixed with other minerals such as nickel, copper, and aluminum to make it durable for jewelry. As you probably know, gold is measured in karats to indicate its purity; pure jewelry grade gold is 24 karats of gold content. A 14k gold piece, for instance, indicates 14 parts gold and 10 parts alloy. 12 karat gold is composed of about half gold – 12 parts gold to 12 parts additive.
It’s the combination of minerals in the gold mixture that gives different kinds of gold jewelry their unique color. Goldsmiths and jewelers have specialized recipes for blending metals to perfection of hue and texture.
White gold is made when gold is combined with nickel or silver, and sometimes platinum or palladium.
In many countries, nickel alloys are not used because of a common allergic reaction some people have when their skin is exposed to nickel. If you’ve ever had a rash from wearing gold, you’re not alone: about 1 in 8 people who wear nickel alloy will develop contact dermatitis. For this reason, platinum alloy – though more expensive – is usually preferred.
Rose gold gets its color from high levels of copper that give it a pink blush. The more copper, the stronger the reddish color.
Mixing silver or zinc with gold gives it a creamier color, or in some cases greener.
Popular “Black Hills” gold – a South Dakota specialty – is composed of several of these alloys to achieve its distinctive multi-tone appearance.
Black gold is not an alloy, but the result of electroplating or synthetic oxidation with certain minerals on the gold’s surface.
If you’ve ever had a piece of jewelry turn your skin green, it’s because of the copper content. Acids in silver alloys oxidize on contact with the skin and can leave a dark stain.
These reactions, unlike a nickel allergy, are quite harmless and may be more or less noticeable depending on your body chemistry. They are more common with lower grade metal alloys. To reduce their effect, avoid using lotions and soaps with your jewelry on. Keep your jewelry clean and your skin dry.