Tarnishing causes metal items to lose their shine and develop a dull, discolored layer. While pure gold, a noble metal, does not tarnish or rust due to its chemical stability, most gold jewelry consists of gold alloys. These alloys, which combine gold with other metals, can tarnish over time.
Understanding Gold Alloys
Pure gold (24-karat or 24K) is exceptionally soft and malleable, making it impractical for everyday jewelry. To enhance its strength, durability, and sometimes alter its color, gold is combined with other metals to create an alloy. This process involves melting pure gold with metals like copper, silver, nickel, palladium, or zinc.
The purity of gold in an alloy is measured in karats, with 24K representing 99.9% pure gold. Common jewelry karats include 10K, 14K, and 18K. For example, 10K gold contains 10 parts gold and 14 parts other metals (41.7% pure gold). 14K gold is 14 parts gold (58.3% pure gold), and 18K gold is 18 parts gold (75% pure gold). The specific mixture of these non-gold metals influences the alloy’s properties, including hardness, color, and susceptibility to tarnishing.
Why Gold Alloys Tarnish
Gold alloys tarnish because of the non-gold metals mixed within them. Unlike pure gold, which resists chemical reactions with oxygen and sulfur, these other metals are reactive. When exposed to air, moisture, and certain chemicals, these base metals undergo oxidation. This reaction forms a thin layer of compounds, such as metal sulfides or oxides, on the surface, appearing as a dull or darkened film.
Common culprits include copper and silver, often found in gold alloys. Silver reacts with sulfur compounds, like hydrogen sulfide in the air, to form silver sulfide, a dark discoloration. Copper can also oxidize, leading to darkening or greenish discoloration. Environmental factors such as humidity, air pollution, and natural oils and perspiration from skin (containing sulfur compounds and acids) accelerate this process.
Exposure to household chemicals like cleaning products, perfumes, lotions, and chlorine (found in pools) speeds up tarnishing by reacting with the alloyed metals. The karat of the gold alloy directly impacts its resistance to tarnish; lower karat gold (e.g., 10K or 14K) contains a higher proportion of reactive non-gold metals. This makes lower karat alloys more prone to tarnishing than higher karat gold, like 18K, which has greater pure gold content.
Preventing and Cleaning Tarnish
Minimizing exposure to tarnishing agents preserves the luster of gold alloy jewelry. Store gold items in airtight containers or anti-tarnish bags to reduce contact with moisture and sulfur-containing gases. Avoid wearing gold jewelry when showering, swimming, or engaging in activities that cause excessive sweating, as moisture and body oils accelerate tarnishing.
Keep jewelry away from harsh chemicals in cleaning products, perfumes, hairsprays, and lotions. Apply cosmetics and perfumes before putting on jewelry, allowing them to dry and minimize contact. Regularly wiping gold alloy pieces with a soft, clean cloth after wear removes surface contaminants like oils and dirt that contribute to tarnish buildup.
If gold alloy jewelry tarnishes, gentle cleaning methods restore its shine. A mild dish soap mixed with warm water can be used with a soft brush or cloth to gently clean the surface. Rinse the jewelry thoroughly with clean water and dry it completely with a soft, lint-free cloth to prevent water spots and further tarnishing. Avoid abrasive cleaners or harsh chemicals, such as toothpaste or baking soda, as these can scratch the metal or damage its finish. For stubborn tarnish or delicate pieces, professional cleaning by a jeweler may be necessary.