Why does Silver tarnish?
Silver tarnish, oxidation, black spots, patina and prevention tips.
Silver has long been used to fashion serving pieces, decorative items, jewelry, and a host of other goods. Many people shy away from collecting Silver wares because they were scared of tarnish. The truth is Tarnish is not as scary as what many may think. It may be much simpler than many has thought.
Silver like gold is both a noble metal and also a precious metal. But in fact, the most plentiful of all metals falling into this "precious metal" category. Then what about Silver as a Noble metal? Noble metals are metals that are resistant to corrosion and oxidation even in moist air. A lot of people think tarnish is due to oxidation. The truth is that Silver do not react with oxygen or water under normal room temperate.
Then what causes Silver to oxidized?
Silver in its pure form is 99.9% or called fine Silver, but silver is actually too soft to be used for manufacture without mixing it with other metals. When metals are combined, they are referenced as alloys. Fine silver is commonly alloyed with copper or zinc. Thus, most silver, including Sterling (92.5% Silver) or Chinese Export Silver (mostly 85% or 90% Silver), falls into this alloy category. It is the Copper or Zinc that oxidized.
Tarnish! Tarnish! Arrest the Culprit
The truth is that tarnish develop as a result of chemical reaction. Sulfur in the air causes tarnish. Silver tarnishes in environments containing various sulfuric gases, even in very low concentration. The first reaction is thought to occur in a thin film of water on the silver surface. In dry air, tarnishing cannot take place. Silver react with sulfur and sulfur compounds to produce silver sulfide or tarnish. All silver tarnish. It is a natural process. The degree and speed of tarnishing is determined by the relative humidity, room temperature, gas concentration, and the length of time the silver is exposed to the gases.
Contacts with Sulfur producing items also causes Silver to Tarnish. Examples are:
- Rubber bands
- Smoke from burnt raw fuel, such as coal or oil
- Skin Oil
- Sweat (Human sweat contain sulfur and chloride)
The good thing about tarnish is that it only dull or blacken the top layer of the Silver. The underlying areas are still well protected.
On pieces that are chased or with repousse, the tarnish that is so difficult to get out of the low relief, the area should actually be left unpolished. It serves as a deliberate contrast to the high relief. The dark patina on the lower relief gives the Silver piece depth.
Sometimes, one might find unsightly black deposits on the Silver surface. These spots are as a result of corrosion of the alloy metal such as zinc or copper and is usually not easy to removed. These corrosion may also be formed as a result of prolong contact with corrosive agent such as acid (Tomato Sauce) salt, detergent in dish washer.
Tips: Wash sterling silver separately from other metals to prevent black spots. Avoid washing Silver in metal sink. Metal sink can causes black spots on your Silver object and may also scratch your Silver piece.
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