by: Ted Beyer
The holidays have just passed, and for most people, part of the celebration involves getting out the “good” china and flatware to set a festive table. Like most people, I have a few pieces of silver and silver plate that don’t get a lot of use, but are nice to use on special occasions. Thing is, over time, silver tarnishes – it turns dark, and if allowed to continue long enough, it turns black. So out comes the polish and you get to spend all kinds of time polishing it. And with silver plated items, if you do that often enough, eventually, you will polish the silver completely off!
But wait – science will come to the rescue!
The tarnish is actually the result of a chemical reaction between the silver and sulfur-containing substances in the air. The silver is actually combining with sulfur and forming silver sulfide. Silver sulfide is black. When a thin coating of silver sulfide forms on the surface of silver, it darkens the silver. That’s what we call ‘tarnish.’
There are two ways to remove the offending silver sulfide. One way is to strip it from the surface. The other is to reverse the chemical reaction and turn silver sulfide back into silver. Polishes that contain an abrasive shine the silver by rubbing off the silver sulfide and some of the silver along with it. Another kind of tarnish remover dissolves the silver sulfide in a liquid. These polishes are used by dipping the silver into the liquid, or by rubbing the liquid on with a cloth and washing it off. These polishes also remove some of the silver.
Obviously, the better way to do away with the tarnish is to reverse the reaction that created it in the first place, and save your silver! This is something that is easy to do at home with commonly found items. It’s a nifty technique for silver or silver-plated objects, but probably not something you’d want to attempt on your most valuable or antique silver pieces.
You will need:
- Your tarnished piece of silver
- A container large enough to completely immerse the silver in (think roasting pan…)
- Aluminum foil to cover the bottom and sides of the pan
- Tap water (enough to fill your pan so you can completely immerse your silver)
- A pot to heat the water
- Pot holders – you will need these to handle the pot of hot water
- Baking soda (about 1 cup per gallon of water)
Line the bottom of the pan with aluminum foil. Place the silver object on top of the aluminum foil. Make sure the silver touches the aluminum. Place the pan in an empty sink.
Heat the water to a full rolling boil. Remove it from the heat – the next step will make the water froth a bit and it may spill over, so be careful! Add about one cup of baking soda for each gallon of water. (If you need only half a gallon of water, use half a cup of baking soda, etc.). As I mentioned, this will cause the water to froth quite a bit and it may boil over the top of the pot. That’s ok. Immediately pour the hot baking soda/water mixture into the pan, and so that it completely covers the silver. Almost immediately, the tarnish will begin to disappear. If the silver is only lightly tarnished, all of the tarnish will disappear within several minutes – or even seconds! If the silver is badly tarnished, you may need to reheat the baking soda and water mixture, and give the silver several treatments to remove all of the tarnish.
You will notice that often the water will look slightly yellowish and dirty and smell faintly of rotten eggs. That is the sulfur that has been detached from the silver. I found that when using this process, trying to re-use the solution more than twice really slowed the reaction down. Since baking soda is cheap, I just make up a new batch of water and baking soda every two or three treatments.
You will also notice that the silver will dry with a bit of a white residue on it. That is just residual baking soda – a quick rinse in clean water and a dry with a towel will make that disappear, leaving you with nice bright silver.
And now for the real science:
As previously mentioned, this tarnish-removal method uses a chemical reaction to convert the silver sulfide back into silver. Many metals in addition to silver form compounds with sulfur. Some of them have a greater affinity for sulfur than silver does. Aluminum is one of them – and luckily, most people already have lots of it in a convenient to use form in their kitchens. In this case, the silver sulfide reacts with aluminum. In the reaction, sulfur atoms are transferred from the silver to the aluminum, freeing the silver metal and forming aluminum sulfide. Chemists represent this reaction with a chemical equation.
The reaction between silver sulfide and aluminum takes place when the two are in contact while they are immersed in a baking soda solution. As with almost all chemical reactions, the reaction is faster when the solution is warm. The solution carries the sulfur from the silver to the aluminum. The aluminum sulfide may adhere to the aluminum foil, it may be found floating in the water having detached from the foil or it may form tiny, pale yellow flakes in the bottom of the pan.
The silver and aluminum must be in contact with each other, because a small electric current flows between them during the reaction. This type of reaction, which involves an electric current, is called an electrochemical reaction. Reactions of this type are used in batteries to produce electricity. Hopefully, this little bit of science will make your future holiday preparations faster and easier – not to mention saving your silver to be enjoyed for many years to come.