How to clean silver
Saturday 26th November 2016
Many people have old silver tea sets or commemorative bowls of silver or copper all of which tarnish over time. The usual method of restoring the shine is to buy silver or copper polish and rub it on the object. That method is messy and sometimes hard work. There is a much easier way to clean silver and copper using things you already have around the house. The photos show my results at cleaning a silver bowl and some copper objects. I cleaned just half of each object to show the before and after.
The Procedure for Silver:
Place aluminum foil (shiny side up) in the bottom of a non-metallic container big enough to hold the piece to be cleaned. Add two teaspoons of salt and baking soda, then fill with hot tap water making sure the salt and baking soda are dissolved.
Place the object to be cleaned in the container so that it touches the aluminum foil. Light tarnish will disappear in a few seconds. Leave the piece in the solution for several minutes for stubborn tarnish. No rubbing required except to dry the piece. I have cleaned most of the family silver with this method and it works well.
The bowl photo shows the results of 10 minutes of treatment on the top half of a very heavily tarnished bowl. By the way, I found it very difficult to photograph a very reflective silver bowl.
Why it works (I think):
Tarnish on silver is principally silver sulfide or silver sulfate. The sulfur comes from the atmosphere and slowly combines with the silver. This method of removing tarnish relies on the fact that silver and aluminum have different standard electron potentials. When the two metals are in an electrolytic solution (salt water) and are connected electrically (touching), electrons can travel between the two. The silver will be reduced (gain electrons) to form pure silver (which plates out on the silver piece) and the aluminum will be oxidized (lose electrons). This causes the sulfur in the tarnish to transfer to the aluminum. In this situation salty water acts as the electrolyte that allows the electrons to flow and the baking soda forms a weak acid which also aids electron flow. The reaction is: silver sulfide + aluminum > silver + aluminum sulfide or 3Ag2S + 2Al > 6Ag + Al2S3. (If the piece is very heavily tarnished the baking soda may take up some sulfur to form H2S, rotten egg gas.)
The Procedure for Copper:
Copper is a bit harder to clean because it requires some rubbing. The tarnish on copper is usually copper sulfide, copper sulfate, or copper chloride which are removable with acid. The most common acid you have around the house is vinegar. (You can also use lemon juice.) The basic method is to soak a cloth or a kitchen sponge in vinegar, dip it in salt to make a mush, then rub the copper piece with it. The salt acts as a mild abrasive. The photo shows my results with this procedure on two old copper coins, left over from a trip to England, and a piece of native copper. I rubbed about half of each object with the vinegar and salt for about 30 seconds using a kitchen sponge,. There are several variations of this method shown here: http://www.wikihow.com/Clean-Copper. For really stubborn tarnish, one method is to boil the piece in a mixture of water, vinegar, and salt. Another is to coat the object with ketchup (really) and let it sit for a while (ketchup has vinegar in it). Note: these methods will not work on lacquered copper.