Pure gold is a mined mineral of bright orange-yellow color. There has never been any gold color, other than yellow. I can’t stress this enough because I hear terms like “pure white gold” way too frequently.
Now, if pure gold is yellow, how come we have jewelry that is made of white, rose, and green gold? Also, what do 18K, 14K, 12K mean exactly?
90%+ of gold jewelry you see on the market is not made of pure gold, but of gold alloy. Gold alloy is a mix of pure gold and other metals.
The use of gold alloys instead of pure gold in jewelry has practical, financial, and aesthetical reasons:
Durability. Pure gold is rather soft. If you don’t want your ring to carry the imprints of the objects you grab or bump into, or if you want a sturdy reliable prong setting for that precious stone, pure (24K) gold may not be the best choice.
Weight. Pure gold is heavy! Gold atoms weigh almost four times as much as iron atoms. So, those pure gold “statement” earrings may pull your ears hard enough for you to get a headache (and stretched earholes over time).
Cost. Naturally, if a pure gold piece weighs more, it costs more. And gold is quite expensive. Just for the reference, an ounce of pure gold costs 75 times more than an ounce of pure silver. Gold is also twice the price of platinum nowadays.
Color variety. We like the color options! Mixing gold with other metals creates various color possibilities. When we add other metals we get white, champagne, rose, and green gold colors.
In the UK and US the pure gold content in the alloy is measured in karats/US or carats/UK. (not to confuse with precious stone weight, which is also measured in carats). Hence we have 18K, 14K, 12K, and so on jewelry stamps. They indicate the pure gold content in your piece.
In the rest of the world, fineness/hallmark measurement is used – 750, 585, 500, etc. Fineness measurement is more intuitive as it directly indicates the percentage of gold in your piece (750 = 75%, 585 = 58.5%, and so on). Why did the British and Americans have to complicate things with karats, I have no clue, but okay. Here is the chart to make it easier:
*No other metals are added to 24K /.999 gold. However, it cannot be classified as 100%, as even the finest purest mineral will contain some minuscular particles of other minerals.
What other metals are used in gold alloy? Silver, copper, zinc, nickel, and palladium. The number of other metal particles will determine the gold alloy color.
Nickel with rhodium plating = pure white
Nickel without rhodium plating = warm “champagne” white
Palladium = slightly grayish white
Copper = rose or pink
Silver = green
The color intensity is dictated by the gold karat value of a jewelry piece. For example, 18K rose gold ring contains 75% of pure gold and 14K ring contains 58.5% of pure gold. 14K gold ring will look more pink and 18K will look more golden, as the copper content in 14K is much higher than in 18K.
The same applies to white gold and green gold alloys – the higher the karat value, the more “gold-like” the piece will look color wise.