3 January 2008
Sterling silver is an alloy of silver containing 92.5% pure silver and 7.5% other metals, usually copper. The minimum millesimal fineness is 925.
The term "Sterling Silver," in reference to the .925 grade of silver, emerged in England by the 13th century.
The terms "sterling" and "pound sterling", seem to have acquired their meaning over a while, and from several convergent sources. The first mention is that of "sterilensis" in 1078, and by the thirteenth century (the 1200s) the term sterling had appeared. "Sterling" is believed to come from the Old Norman French esterlin (meaning little star) and Old English stiere (strong, firm, immovable).
As the purity of the silver decreases, the problem of corrosion or tarnishing also increases.
Chemically, silver is not very reactive — it does not react with oxygen or water at ordinary temperatures, so does not easily form a silver oxide. However, the other metal in the alloy, usually copper, may react with oxygen in the air.
The black silver sulfide (Ag2S) is among the most insoluble salts in aqueous solution, a property that is exploited for separating silver ions from other positive ions.
Sodium Chloride (NaCl) or common table salt is known to corrode silver-copper alloy, typically seen in silver salt shakers where corrosion appears around the holes in the top.
Several products have been developed for the purpose of polishing silver that serve to remove sulphur from the metal without damaging or warping it. Because harsh polishing and buffing can permanently damage and devalue an antique piece of silver, valuable items are typically hand-polished to preserve the unique patinas of older pieces. Techniques such as wheel polishing, which are typically performed by professional jewelers or silver repair companies, are reserved for extreme tarnish or corrosion. An easy way to shine silver is to take some dry baking soda and rub it on the metal with one's fingers, then to rinse it with mineral-free water