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19 July 2010

Archives October 2009 : Question and Answer

Q: Why does silver tarnish?

A: Tarnish is a thin layer or film that forms over copper, brass, silver, aluminum and other semi-reactive metals as their outermost surface undergoes a chemical reaction. While silver is almost completely resistant to oxygen, other chemicals in the air, such as sulfur, creates a chemical reaction forming Silver Sulfide on the surface. The reaction occurs slowly, first with a thin sulfide layer causing the surface to yellow. As time proceeds, the layer will turn a dull gray or black.

Tarnish will also appear when sterling objects are in direct contact with skin. While everyone's body chemistry varies. Sulfur is found in skin oils and also in many cosmetics causing the rate of tarnish to increase dramatically.

How do I prevent tarnish?
The only sure fire way is to exclude sulfur from reacting from the surface of the metal, which would include keeping the metal piece in an air tight case filled with an inert gas which is virtually impossible! But here are some more reasonable options:

Rhodium Plating: through an electrolytic process a thin layer of rhodium (an expensive member of the platinum family) is applied to the surface of the silver. This layer is super hard and super white in color, resembling chrome. The downsides to rhodium plating are:
1. The color difference. The rich, warm white color of silver is replaced by the cold blue-white color of rhodium.
2. The plating layer is very thin and will wear with time.
3. Besides the cost of equipment for plating, rhodium is an expensive solution.

Coating the surface with Lacquer or Wax: Using a Lacquer or wax to seal the polished metal surface from exposure to air is a reasonable option if the piece will not be worn or used. However, in cases of wear or use, the areas of exposure to the skin or abrasion will quickly rub off the protective layer.

Periodic Cleaning: I sell my jewelry and I offer purchase of a polishing cloth to keep jewelry clean. The polishing cloth has a polishing chemical imbedded in the fabric. Assuming the wearer uses the cloth on a consistent basis (ie weekly), tarnish will be prevented or the slight effects (yellowing) will be removed. However, if the cloth is washed, the chemical is removed from the fabric and is no longer useful. Other possibilities are gels with brushes; small, home ultrasonic machines and steam cleaners; polishing on buffing machines.

Tarnish Removers: These are chemicals that the jewelry can be dipped into to instantly remove the tarnish. While these work almost instantly, the way the chemical works is that it eats away at the surface, removing the tarnish. So keeping this in mind, the surface of the metal is being eaten away, so if the metal is left in too long, it will eventually ruin or disintegrate the piece. Keeping this in mind, any polishing compounds on the surface of the metal preventing tarnish are now removed and the silver will tarnish at a higher rate (sometimes within hours) if not polished with a polishing cloth or on a buff shortly thereafter.

Using Argentium Silver: Argentium Silver is a new sterling silver alloy made with germanium. Germanium oxidizes preferentially to the silver and copper in Argentium Silver, to form a transparent germanium oxide surface layer. The alloy is not completely resistant to tarnish, but will slow the process of tarnish. Germanium causes the silver to react differently than normal sterling silver; so if you choose to use this, make sure you do your research! (At this time JFF does not carry Argentium)

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