Silver often changes color over time, leading many to wonder if it can turn green. Understanding these changes involves looking at the specific composition of the metal itself.
The Truth About Silver Discoloration
Pure silver, also known as fine silver (99.9% pure), primarily tarnishes black or dark brown. This discoloration is due to the formation of silver sulfide on its surface. The green discoloration, however, is almost exclusively associated with sterling silver and other silver alloys. Sterling silver contains 92.5% silver and 7.5% other metals, most commonly copper.
The copper content in these alloys causes any green or bluish-green residue. When copper oxidizes, it develops green pigments. While pure silver does not turn green, the copper in silver alloys can certainly exhibit such a change.
Why Silver Changes Color
Silver changes color primarily through two distinct chemical processes: sulfidation and oxidation. Sulfidation occurs when silver reacts with sulfur compounds in the air, forming a thin layer of silver sulfide. This reaction causes pure silver to develop its characteristic black or dark brown tarnish. Sulfur is a naturally occurring element found in various environmental sources.
Oxidation involves the reaction of metals with oxygen. In silver alloys, particularly sterling silver, copper reacts with oxygen to form copper oxides. These copper oxides can further react with substances like carbon dioxide, forming copper carbonates, which often appear green or bluish-green. While distinct, both sulfidation and oxidation can occur simultaneously on sterling silver, contributing to its varied discoloration.
Common Factors Accelerating Tarnish
Several environmental and chemical factors can accelerate silver’s tarnishing. High humidity provides a favorable environment for chemical reactions on the metal’s surface. Air pollutants, especially sulfur compounds, contribute to silver sulfidation. Exposure to these elements speeds up the formation of tarnish.
Skin oils and perspiration also contain compounds that react with silver and its alloys. Cosmetics, lotions, and perfumes often contain chemicals that can cause or accelerate discoloration upon contact. Household cleaning products and certain foods, particularly those high in sulfur like eggs or onions, can also accelerate tarnishing.
Caring for Your Silver
Proper care can help prevent and minimize silver tarnish, preserving its luster. Storing silver in airtight containers or anti-tarnish bags helps limit its exposure to air and pollutants. Anti-tarnish strips within storage containers can further absorb sulfur compounds, offering additional protection. These methods create a barrier against environmental factors that cause discoloration.
When wearing silver, avoid contact with chemicals in perfumes, hairspray, and cleaning products. Removing silver jewelry before swimming or exercising can also prevent exposure to chlorine and sweat, both of which accelerate tarnishing. For cleaning, gentle polishing cloths can remove light tarnish. For more stubborn discoloration, a mild soap and water solution or a paste made from baking soda and water can be effective.