Why costume jewellery turns your finger green (and how to avoid it)

You take the ring off and there is a green ring underneath. It is not that the piece is bad, and it is not that you are dirty: it is chemistry, and fairly basic chemistry at that.

Where the green comes from

From copper. It is in almost every alloy used in jewellery: in brass (copper and zinc), in bronze (copper and tin), and in sterling silver too, which is 92.5% silver and 7.5% other metals, nearly always copper.

When that copper meets damp, the acids in sweat and the oxygen in the air, it forms copper salts. Those salts are green — it is the same green as bronze statues and copper roofs — and they stay on the skin, which is porous and absorbs them. They come off with soap and water, they do not stain clothes and they are not toxic.

Why me and not my sister?

Because the reaction depends as much on the skin as on the metal. The things that really change the outcome:

• The pH of your skin. More acidic skin dissolves copper sooner. It is genetic, and it also shifts with diet and hormones.
• How much you sweat. Which is why it happens more in summer, and more on hands than on ears.
• What you put on top. Creams, perfumes, hand sanitisers and sun cream speed the reaction up; some medicines change the composition of your sweat.
• Rubbing. A ring rubs against everything all day long; a pair of earrings, hardly at all. The ring is always the piece that marks most.

The five things that prevent it

1. Do not sleep in the piece. Eight hours of contact with no air and plenty of damp is the worst case there is.
2. Put it on after the cream and the perfume, not before. And with dry hands.
3. Always dry it when it gets wet, with a soft cloth, instead of letting it dry against your skin.
4. Store it dry and separately, not in a heap in a drawer. The damp air of a bathroom oxidises even the pieces you never wear.
5. A barrier layer on the inside. Clear nail varnish works, but it chips off within a few weeks and has to be redone; a zapon lacquer for metals lasts a good deal longer. With either one, only on the inner face.

Which materials do not mark

If the green mark matters to you more than anything else, the materials that do not leave it are the ones with no free copper in contact with the skin:

• Surgical stainless steel (316L): the most stable of the affordable materials.
• Titanium: inert, light, and the most expensive to work.
• Solid gold, 18 kt or higher: it does have copper in the alloy, but in a low proportion and very stable.
• Rhodium-plated silver: the rhodium layer acts as a barrier for as long as it lasts.

Everything else — including any plated piece — depends on the coating staying intact.

And our pieces, do they mark?

With the plating intact, no: our pieces are bronze with 24 kt gold plating over a layer of palladium, and as long as those two layers cover the metal, the copper in the bronze does not touch your skin. The palladium is there precisely as a barrier, and it is what lets them stand up to daily wear.

And there are two layers, which is the part that matters here: the palladium is not only there to hold the gold, it slows the copper from migrating out of the bronze towards the surface. For the copper to reach your skin, both would have to wear through, not one. That is why a piece with a barrier and any old gold-coloured costume jewellery do not behave the same way, not by a long way.

That said, plating can be worn away where a piece rubs constantly — the inside of a ring, the clasp of a chain — and the barrier with it. Once it gets to that point, the mark can appear in that spot. We write this down because it is how plating works and we are not going to tell you a different story; and the five rules above push it much further away than it might seem. The detail of why plating wears out is in gold plating explained.

And if what worries you is not the mark but itching or redness, that is something else: it is in jewellery and sensitive skin.