Metal · Au, 79, alloyed to be usable
Gold
Every piece of jewelry is an alloy. The gold decides the value and the other quarter decides the colour, the hardness and the rash.
The colour is in the alloy
In 18 carat, 250 parts per thousand are something other than gold, and that quarter decides the colour entirely. Roughly equal silver and copper gives standard yellow. Copper dominant, around 200 parts to 50 of silver, gives rose, and more copper means pinker and harder. Palladium and silver, sometimes with nickel, give the pale grey alloy sold as white gold.
The practical consequences are specific. Rose gold is harder and more scratch resistant than yellow, and its copper content can leave a harmless green mark on some skin in humid weather. White gold is not white and must be plated. Yellow gold at the same carat is the softest of the three.
Rhodium, the coat of paint
White gold jewelry is electroplated with a micron or two of rhodium, a platinum group metal that is brilliantly white and very hard. It looks superb. It is also a surface layer that wears, and on the underside of a ring worn daily it thins within eighteen months to three years, at which point the warm grey underneath begins to show. Replating costs 40 to 90 and is a permanent maintenance item.
The second consequence is allergy. Nickel bearing white gold with intact plating causes no reaction. Once the plating wears through, the nickel is in contact with skin, and a ring that has been comfortable for two years suddenly is not.
Wear, which is metal leaving
Gold is soft, and a ring worn daily loses metal continuously. After thirty years a band is measurably thinner, and this is the reason old rings develop a knife edge and eventually split. It cannot be reversed, only rebuilt by adding metal. Platinum behaves differently: a scratch displaces metal into a ridge rather than removing it, which is why a platinum band of the same age has the same mass.
Fineness
Stamped inside the band. The number is parts per thousand.
How to check it
- Find the fineness stamp inside the band: 750, 585, 375. No stamp means unverified, and a jeweller test costs almost nothing.
- Look at the underside of a white gold ring in daylight. A warm grey cast against the top surface means the plating has gone.
- Gold plated, gold filled and vermeil are three different things. Plated is microscopic, filled is a bonded layer of defined thickness, vermeil is gold over sterling silver.
- Weigh it in the hand against a platinum piece of the same size. Platinum is noticeably heavier and the difference is unmistakable.
Care
- Keep chlorine away from alloyed gold. It attacks the copper and silver in the alloy and can cause stress cracking.
- Clean in warm water with a drop of washing up liquid and a soft brush. Hand cream in a setting dulls a stone faster than anything else.
- Take rings off for the gym. Most bent bands come from gripping a bar.
- Have prongs checked annually. Retipping costs 20 to 60 and prevents almost every stone loss.