Reason why silver discolors
Silver reacts with sulfur (or sulfur compound) in the air (or in the water) at room temperature to form silver sulfide easily. Along with the process of forming silver sulfide, silver changes color in turn from white to yellow, gold, red, blue, green and finally black. Oxidization of silver is a surface treatment that actively utilizes sulfidation. |
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Preventing discoloration
If a silver surface is exposed to the air (or water) for a long period of time, it will gradually sulfidize. If you do not use silver work, store it dry in a place where the air has been removed. A sealable bag is convenient. It is possible to apply a coating agent to the surface to prevent discoloration. The agent is available from jewelry stores or retail stores that handle PMC. Please note that the effect is not permanent. |
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To restore the color
Because only the surface of silver is sulfidized, commercially available silver care cloth or soft cloth containing abrasives to polish the piece will restore the silver color. If the piece is composed of PMC only, it may be re-fired (for a few minutes at 800 to 900 degrees Celsius). After re-firing, the tarnish disappears. In this case, surface becomes a matt finish, thus mirror finishing is required again, if the original work had such surface.
You may also immerse the item in commercially available silver cleaning agent. The principal ingredient of the agent is thiourea in dilute sulfuric acid solution, which eliminates sulfur with a chemical reaction (oxidation-reduction). Because it contains sulfuric acid, be careful and avoid touching the solution with bare skin. You need to rinse the piece after treatment. |
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