Pure gold is a mined mineral of bright orangey-yellow color. There has never been any gold color, other than yellow. I can’t stress it 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 a very soft and malleable metal, and it will not hold shape impeccably in many designs, especially rings. If you don’t want your ring to carry the imprints of the objects you hold or bump into, or if you want a sturdy reliable setting for that precious stone, pure (24K) gold may not be the best choice.
Weight. Pure gold is heavy! Gold atom weighs almost four times as much as the iron atom. 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 pure gold piece weighs more, it costs more. And gold is quite expensive. Just for the reference, the ounce of pure gold costs 75 times more than 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, no gold can 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 higher percentage of gold in a piece will result in more yellow and less other color. For example, 14K rose gold will be pinker than 18K rose gold. Since 14K piece contains 58.5% of pure gold and 18K piece contains 75% of pure gold, the content of copper in 14K will be higher, which will result in more pink coloring.
The same applies to white gold – the higher the karat value, the “yellower” the piece will look. That’s why rhodium plating is applied to the surface to make the piece more “white”. I personally prefer the natural warm champagne color of white gold and don’t rhodium plate my work, unless specifically requested. Rhodium plate needs to be reapplied over time, because as any plating it will eventually wear off, especially on rings.