What Causes Tarnish?
Like rust, silver tarnish is a form of corrosion.
When people think of metals and moisture, they more than likely anticipate rust as the result. This line of thinking is often applied to silver tarnish as well…but this is NOT the case.
If you’re concerned about your silverware or silver jewelry tarnishing and turning black, then you’ll want to fully understand their process of corrosion.
Silver tarnish does not occur in the same way that traditional rust occurs.
What is Silver Tarnish?
What we refer to as tarnish is scientifically known as Silver Sulfide.
Silver Sulfide (Ag2S) occurs when Silver (Ag) comes in contact with Sulfur (S).
It’s a dense solid that turns silver’s generally shiny exterior into a darkened and dull one.
Tarnish (Silver Sulfide) has plagued silversmiths and silver owners since its onset and utilization by humanity. As you may have surmised from the chemical formula above, water/water vapor (H2O) IS NOT part of the equation.
Just because moisture doesn’t directly result in the rusting of silver - it’s a noble metal and therefore resistant to corrosion and oxidation in moist air - doesn’t mean that moisture’s role in tarnish can be ruled out entirely.
The Role of Moisture in Silver Tarnish
The science used in this blog has been fairly straightforward thus far, but here’s where it gets a little tricky! We’re going to keep it as simple as possible!
If Silver (Ag) is a noble metal and therefore naturally resistant to corrosion and oxidation from moisture, how could moisture have any effect on tarnish?
Great question! Here’s the answer:
Moisture and humidity may not have an effect on silver, but it does have a profound effect on Sulfur (S).
Remember, sulfur is the crucial ingredient in the development of silver tarnish (Ag2S). When sulfur reacts with silver, you get tarnish.
The effects of temperature, moisture and its distance to sulfur influences silver’s corrosion rate.
Corrosion rates increase as temperature and humidity increases because sulfur vapor pressure is more intense at higher temperatures.
In order for temperature and humidity to influence silver’s corrosion rate, sulfur molecules must be present and nearby. Therefore, the corrosion rate slows as the distance between the sulfur source and the silver increases.
Temperature and relative humidity alone do not play a major role in causing corrosion. Rather, the interaction between sulfur molecules and the silver’s surface determines the corrosion rate.
Is Sulfur the Only Cause of Tarnish?
YUP – THAT’S THE ONLY CAUSE!
You could place silver in a room with 99.9% humidity and so long as no sulfur is present, no tarnish will occur.
People (myself included) naturally assume that if moisture comes in contact with a metal then corrosion occurs. Since silver is a noble metal, however, moisture itself has no direct effect on it.
But if you think only having to defend against one variable (sulfur/sulfuric compounds) is easy though, you’re mistaken!
How Common is Atmospheric Sulfur?
Atmospheric sulfur is more prevalent than you might think. As a matter of fact, regardless of the location of your home or store, you’re more than likely being exposed to it in some form.
100% pure sulfur – just like any other element – is a rarity. Sulfur compounds, on the other hand, can be found almost everywhere.
Sulfur Dioxide (SO2) and Hydrogen Sulfide (H2S) occur naturally through the breakdown of organic compounds and production of volcanic & natural gasses. They’re mostly produced through human activity, however.
If you think the presence of sulfuric compounds in the atmosphere is a bunch of hoopla, then simply expose any silver you own to the air for a few days. Even inside your home, silver sulfide will begin to form on your silver’s exterior.
We don’t mean to sound dramatic, but there’s simply no escaping the presence of sulfuric compounds in our atmosphere. This is especially true in areas of the world with less stringent environmental laws and higher rates of pollution.
- The only element that causes silver tarnish is sulfur.
- Silver tarnish is a form of corrosion.
- Silver tarnish is chemically known as Silver Sulfide (Ag2S).
- Silver is a noble metal and, therefore, not reactive with moisture alone.
- Moisture and humidity alone WILL NEVER CAUSE silver to tarnish.
- Moisture has an effect on silver tarnish because it has an effect on sulfur.
- As the vapor pressure of sulfur rises, so too does the rate of silver corrosion.
We hope you found this blog informative! It’s important to know the science behind tarnish because it gives you a better idea of how to subdue it!