The science of silver tarnish and what you can do about it
Brace yourself for some science!
Why does silver blacken over time?
We all know that sterling silver can tarnish, and that certain conditions can make this happen even more quickly. We always advise that you don’t wear your silver in the shower, swimming pools, or let it contact creams, lotions, perfumes, soaps etc. But why is this?
The main culprits of the black coating on your piece of silver jewellery are are Silver Sulphide (Ag2S) and Silver Chloride (AgCl)(1). These black deposits form as a result of silver reacting with sulphur and chloride compounds found in so many aspects of our daily life - from water, cosmetics, cleaning products, and even air pollution to name a few.
This reaction can be accelerated by different pH and moisture levels on your skin. Higher humidity speeds up the reaction process - this is because water actually adsorbs to the surface of the silver.
Chemical reactions occur quicker in water because molecules can move around more freely and are more likely to bump into eachother and react. This increase in reaction speed happens even more as the temperature increases. To demonstrate this, a set of experiments showed that silver (in the presence of sulphur) tarnished twice as fast when the relative humidity was 50% vs 0%. Also of note was that as the temperature increased, so too did the speed at which the silver tarnished(2).
So let’s think for a minute about what this means… that lovely, warm holiday where you’re dipping in and out of the pool and using sunscreen - ideal conditions for silver to tarnish!
Some people notice that when they wear a piece of jewellery all the time, it doesn’t tarnish very much, but when you leave it in a jewellery box it can go black in a matter of weeks. This is because the oils on your skin can actually slow down the tarnishing process, as they form a barrier to air and moisture and slow down the reaction process (3). Often the glues used in jewellery boxes release gases which can accelerate the tarnishing process, so make sure you find a jewellery box that uses non-tarnish accelerating adhesives.
So reading this is all very well, but what happens if you ignore every piece of advice here and throw the metaphorical kitchen sink at your silver? Well, I decided I would test this out so you don’t have to.
First I made two near-identical silver pendants. I kept one in a non-tarnishing pendant box (left) and exposed the other to daily 30+ degrees heat, sunscreen and chlorinated pool water! (right)
As you can see, in just one week the exposed pendant had tarnished significantly compared to the one kept in a box. Fortunately, this process is reversible with some simple items you’ll already have at home - a soft-bristled toothbrush and some toothpaste. The mild abrasive in the toothpaste helps to get rid of the tarnish, and it can then be buffed up even more with a standard silver polishing cloth. Do be careful if your piece is set with gemstones though; as soft stones may be damaged by the abrasive compounds in certain toothpastes.
So what’s the takehome message here? To keep your jewellery in tip-tip condition:
When you’re not wearing it, keep your silver dry and in a protective place, like a zip-lock bag or appropriate jewellery box
Don’t wear it in the swimming pool
Don’t let cosmetics / cleaning agents / sunscreen get on it
If you do, you can wash your piece gently in soapy water - just remember to dry it thoroughly after
You can always clean it at home with a gentle toothbrush and a silver polishing cloth.
Even by taking care of your piece of jewellery, some tarnish of silver is inevitable over time. So to help you keep your pieces as shiny as possible, all of our jewellery boxes at Zaphir are constructed with this in mind, using water-based non tarnishing glues. We also include a free polishing cloth with every order above £25. So don’t be afraid to wear and enjoy your precious silver jewellery armed with the knowledge of how to keep it looking brilliant for decades to come!
References:
(1) Novakovic, Jelica & Vassiliou, P & Georgiza, Elsa. (2013). Electrochemical Cleaning of Artificially Tarnished Silver. International journal of electrochemical science. 8. 7223-7232.
(2) Jiang Yang, C., Hao Liang, C. and Liu, X. (2007), "Tarnishing of silver in environments with sulphur contamination", Anti-Corrosion Methods and Materials, Vol. 54 No. 1, pp. 21-26.
(3) PA Gay, P Bercot, J Pagetti - The protection of silver against atmospheric attack - Plating and surface finishing, 2004 - nmfrc.org
