Cleaning silver - the science behind it?

From a site presented by the Society of American Silversmiths:

"Electrochemical (Galvanic) Reduction

"This process uses an aluminum or aluminum alloy plate and warm solution of sodium carbonate (washing soda). When the object comes in contact with the plate in the solution, it removes only light tarnish, not the thick, black tarnish produced by years of neglect.

"Pitting of the object can occur if the aluminum plate is not periodically cleaned. Another not-so-obvious problem is scratching of the object when in contact with the plate.

"Objects cleaned by this method may tarnish more quickly than silver that has been polished, for the object's surface will act like a sponge and more readily absorb tarnish-producing gases and moisture. The solution can also seep into hollow areas such as coffee pot handles, unsoldered spun beads around the tops of lightweight holloware, weighted pieces with minute holes, and any porous attachments. For these reasons, this cleaning technique is not recommended."

You can also use baking soda or an other mild alkali with the foil, I use Sulfamic Acid as a quick dip to clean the copper parts in the induction furnace, I noticed it is the active ingredient in "Tarnex" Alan Black

Silver tarnish is silver sulfide. The sodium carbonate is a basic electrolyte which lets it penetrate the oxide layer on the aluminum to reach fresh aluminum metal which is more electrochemically active than silver. The aluminum oxidizes while the silver reduces to silver metal, so you wind up with aluminum sulfide. The silver deposit is usually a little rougher than the silver surface, so manual polishing really helps to make it look its best. If you just polished the tarnish away you would lose that silver, so this puts it back on the surface, and for mildly tarnished stuff it can look plenty good enough to skip the polishing totally. Really ugly, pitted silver will need lots of elbow grease after the electochemical cleanup.

-- Regards, Carl Ijames carl.ijames at verizon.net

This is not exactly the same thing, but close enough to possibly add to the topic. I have a very old, in the original box, "Maggie Pan," for cleaning silver. The pan is said to be magnesium, and instructions are to use "any detergent."

The secret is the aluminum. You can use sodium bicarbonate and water instead of the water softener.

As others have said, this is an electrolytic reduction of the silver compounds making up the tarnish. You're making a short-circuited electrochemical cell. The salt acts as an electrolyte(but I wouldn't use it) and the water softener probably keeps the calcium in hard water from interfering. Most of those products also have some sort of detergent in them, which would help with wetting the surfaces. The reason I wouldn't use salt is that it'll attack silver all by itself, chloride just loves to combine with silver.

We've used this method for many years in my family, my folks and relatives have some "Dowmetal" griddles that were purchased shortly after WWII. These are largely magnesium and work for this quite well. They're just small enough to sit on the bottom of the kitchen sink. A little squirt of detergent and a couple hours immersion usually brightens up the silverware to the point that it doesn't need further polishing. I've never heard of aluminum being used, but any metal more active than silver could be used as the other plate of the cell. There have been some magnesium-containing products sold over the years to do the same thing, some at very fancy prices. You will occasionally find these griddles at rummage and garage sales for fifty cents or so, they're worth grabbing. They also work very well as griddles. They look like aluminum, but the weight and the "Dowmetal" stamp gives them away.

Stan

Note that it says detergent, not soap. Gerry :-)} London, Canada

Soaps are usually detergents (so is sand , in the right circumstances:-)

Mark Rand RTFM