Cleaning Your Silver

Have you ever polished your valuable silver to get rid of that ugly tarnish? Me, too. However, I just learned from a retired Chem Teacher buddy of mine, John Gilligan, now a teacher-oriented website designer, expert and all-round good guy, that I was removing lots and lots of silver with the cleaning! Wow, and I thought I was doing myself a favor! Here's the poop. Silver tarnishes when sulfur attaches to the silver creating silver sulfate, an unseemly grayish thing that my In-Laws swear is my fault. Chemical applications and any abrasive cleanser/polish will actually remove the entire structure of silver sulfate from the surface, sulfur AND SILVER. Ahh! Along with the silver sulfate, there goes some of the valuable silver, huh? This is especially bad when you are dealing with cheaper silver plated things. The plating may only be a few atoms thick. One good scrubbing can remove most or ALL the silver. So, to alleviate this problem, you must use a method that will remove the sulfur and leave the silver intact. A basic electrolysis lab takes care of this. You will need a sheet of real aluminum foil, hot water, baking soda, table salt and a pan to do this in.

a)      Line your pan with a sheet of Al foil. Place the item to be cleaned, say the crown jewels, on top of the Al foil sheet. Contact is a MUST.

b)      On a stove, heat some water. Enough water to cover the items in the pan to be cleaned. Add some table salt like you are boiling water for spaghetti.

c)      Into this hot water, dissolve a cup or two of fresh baking soda.

d)      Once dissolved and quite hot, pour this over the item making sure contact is maintained between the item and the Al foil.

e)      Sit back and watch the tarnish disappear, leaving all the silver behind where your hard-earned money says it should be.

Why do this happen, you ask? The absolute best chemical description of this is by the famed Bassam Z. Shakhashiri, one of the most famous chem educators of all time. It's worth a trip to his site to check out what's hot in Chem Demos. To paraphrase Dr. Shakhashiri;
The baking soda/aluminum combo pulls sulfur off the silver by a small electrolytic current set up through the "salt bridge". This is why contact with the aluminum is so important. Both Silver and Aluminum loves to accept sulfur, but aluminum does it quicker and will pull atoms of it off the item as long as the electrolytic current remains. The silver is left all alone again. The heat of the water is just a catalyst and makes the reaction occur faster. I've done this recently and was amazed at the results. One of my silver forks actually looks silver again! (I leave the rest of the service for eight to my wife to clean.)

Now, for Dr. Shakhashiri's own explanation taken from Chem Dept Univ Wisconsin at Tarnish Experiment.
When silver tarnishes, it combines with sulfur and forms silver sulfide. Silver sulfide is black. When a thin coating of silver sulfide forms on the surface of silver, it darkens the silver. The silver can be returned to its former luster by removing the silver sulfide coating from the surface. There are two ways to remove the coating of silver sulfide. One way is to remove the silver sulfide from the surface. The other is to reverse the chemical reaction and turn silver sulfide back into silver. In the first method, some silver is removed in the process of polishing. In the second, the silver remains in place. 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. The tarnish-removal method used in this experiment uses a chemical reaction to convert the silver sulfide back into silver. This does not remove any of the 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 such a metal. In this experiment, the silver sulfide reacts with aluminum. In the reaction, sulfur atoms are transferred from silver to aluminum, freeing the silver metal and forming aluminum sulfide. Chemists represent this reaction with a chemical equation.

3 Ag2S + 2 Al 6 Ag + Al2S3
silver sulfide and aluminum "gives you" silver and aluminum sulfide
The reaction between silver sulfide and aluminum takes place when the two are in contact while they are immersed in a baking soda solution. 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, 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.

Addendum 01/15/03 : I've been asked a few times recently if this is actually silver being cleaned or aluminum replacing the sulfides and coating the silver to look cleaner. Hmm. So, I went a searching for my old notes. Alas, they are missing along with Jimmy Hoffa.
I saw this many moons ago at a ChemDen thing at a national NSTA convention. It's been confirmed by Chem folks I know. Here is the text from an
I don't see any mystery here. The hydrogen gas is merely evolved through the reaction of aluminum and sodium carbonate. The hydrogen plays no part in the removal of the silver tarnish (i.e., silver(I) sulfide). Aluminum is a reducing agent, and thereby reduces silver sulfide to elemental silver while forming aluminum sulfide (which is yellow in color). The aluminum sulfide thus formed readily hydrolyzes to form aluminum hydroxide and hydrogen sulfide. So, we really have *two* gasses evolved: hydrogen and hydrogen sulfide, with the quantity of the former being greater than the latter. Aluminum in pure water would not work since the surface film of aluminum hydroxide readily stops further activity. Since hydroxyl ions from the sodium carbonate readily dissolve any aluminum hydroxide thus formed, a ready supply of aluminum ions for reduction purposes is assured. I have used this process, and found that cold water will work, but lukewarm is better. Boiling water will probably work even better, but the aluminium is used up too fast, and the smell is quite bad (probably from H2S or similar). See, I told you there was hydrogen sulfide! :-) Now you know why. I also find that a scum forms on the surface of the water after some time. Probably aluminum hydroxide, formed due to the reverse reaction with evolved hydrogen sulfide.
Larry Lippman @ Recognition Research Corp.
"Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note:] uunet!/ \aerion!larry

So, now you know the rest of the story...

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