Silver tarnish is a common discoloration that appears on the surface of silver items. It typically manifests as a dull, darkened film, ranging in color from yellow or brown to black. This change affects a wide array of silver objects, including jewelry, silverware, and decorative pieces, making them lose their original lustrous shine. Tarnish is a natural chemical process that alters the metal’s outermost layer.
The Chemical Basis of Tarnish
Silver’s tendency to tarnish results from its reaction with specific elements present in its surroundings. Unlike some metals that undergo extensive corrosion, silver primarily reacts with sulfur-containing compounds. The main chemical involved in this process is hydrogen sulfide (H₂S), a gas found in the atmosphere. When silver comes into contact with hydrogen sulfide, a chemical reaction occurs, forming silver sulfide (Ag₂S). This silver sulfide is a dense, black compound that adheres tightly to the silver, creating the characteristic dark layer of tarnish.
Everyday Contributors to Silver Tarnish
Various common sources of sulfur compounds and environmental conditions contribute to the formation and acceleration of silver tarnish.
Atmospheric Sulfur
Atmospheric sulfur, particularly hydrogen sulfide and sulfur dioxide, is a pervasive cause, originating from natural processes like decaying organic matter and volcanic activity, as well as industrial emissions. Even in low concentrations, these airborne compounds can gradually lead to the discoloration of silver over time.
Household Items
Materials such as rubber bands, latex, and certain fabrics like wool contain sulfur compounds that can react with silver. Storing silver items in direct contact with these materials can accelerate the tarnishing process.
Certain Foods
Certain foods are another notable source of sulfur, with eggs, onions, and mustard being common examples. When silver cutlery or serving dishes come into contact with these foods, the sulfur present can initiate or worsen tarnish. The sulfur can also be secreted through skin during perspiration after consuming such foods.
Personal Contact
Natural oils, acids, and salts found in human sweat and skin can contribute to tarnishing. Cosmetics, lotions, and perfumes often contain chemicals that can accelerate the reaction, making it advisable to apply these products before wearing silver jewelry.
Environmental Factors
Beyond direct sulfur exposure, environmental factors like high humidity and heat significantly influence the rate of tarnishing. Increased moisture in the air provides a medium that can speed up the chemical reaction between silver and sulfur compounds. Higher temperatures also accelerate chemical reactions, including the formation of silver sulfide.