Tarnish is a common form of discoloration that occurs when a metal undergoes a chemical reaction with its environment, resulting in a dulling or darkening of the surface. Pure 24-karat gold is chemically inert and does not react with oxygen or sulfur, meaning it will not tarnish. The discoloration observed on jewelry is actually the tarnishing of the non-gold metals mixed in to create a more durable product.
The Direct Answer: The Color of Gold Discoloration
The color of the tarnish on gold jewelry is not the color of corroded gold, but rather the color of the oxidized or sulfidized base metals present in the alloy. The most frequently seen discoloration is a dark gray or black smudge, which is typically silver sulfide. This reaction occurs when the silver alloy reacts with sulfur compounds, such as hydrogen sulfide in the air or from contact with certain materials.
A greenish or reddish-brown hue on the jewelry surface or the skin underneath often indicates a high copper content in the gold alloy. Copper reacts with the moisture and acids present in human sweat to form green copper salts or with oxygen to form reddish-brown oxides. In extreme cases, especially with white or rose gold, blackish tarnish can appear, which looks like a fine layer of soot or grime.
Why “Gold” Jewelry Tarnishes
The reason jewelry labeled “gold” tarnishes lies in the karat system, which measures the purity of the gold content. Pure gold, or 24-karat gold, is too soft for everyday wear, so it is combined with other metals—known as alloys—to increase its strength and durability. The karat number indicates the proportion of gold out of 24 parts; for example, 14-karat gold is 58.3% gold and 41.7% alloys.
These non-gold metals, such as copper, silver, nickel, and zinc, make the jewelry susceptible to tarnish. The lower the karat number, the higher the percentage of these base metals, leading to a greater potential for tarnishing. Ten-karat gold (41.7% gold) has the highest potential for discoloration because the nearly 58% alloy content is highly reactive.
The alloy metals corrode through oxidation (reaction with oxygen) or sulfurization (reaction with sulfur compounds). These chemical changes form a thin, dark layer on the surface that diminishes the gold’s luster. Even 18-karat gold, which is 75% pure gold, contains enough silver and copper to show slight discoloration over time.
External Triggers of Tarnish
The tarnishing process of gold alloys is significantly accelerated by specific environmental and chemical triggers. Chlorine is one of the most destructive chemicals, as it reacts readily with the alloy metals, especially copper, and is commonly found in swimming pool water, household cleaners, and bleach. Repeated exposure to chlorine can not only cause discoloration but may also weaken the jewelry’s structure.
Sulfur compounds, which are naturally present in the air, particularly in polluted or industrial areas, accelerate corrosion. Other common triggers include substances that come into direct contact with the jewelry, such as cosmetics, lotions, and perfumes. These products contain chemicals that can accelerate the corrosive reaction on the surface of the alloy.
Human perspiration and body oils also play a role, as they contain salts and organic acids that react with the base metals. Individuals with more acidic skin chemistry may notice their jewelry tarnishes more quickly than others. High humidity and even saltwater from the ocean provide the ideal conditions for these chemical reactions, making tarnish more prevalent in certain climates.
Preventing and Cleaning Tarnished Gold
Preventing tarnish begins with limiting the jewelry’s exposure to known chemical triggers and moisture. It is advisable to remove all gold jewelry before swimming, showering, applying lotions, or using household cleaning products. Storing the pieces properly in a cool, dry place, such as an airtight jewelry box or an anti-tarnish pouch, minimizes exposure to oxygen and humidity when the jewelry is not being worn.
For routine maintenance, gold jewelry should be gently wiped with a soft, lint-free cloth after each wear to remove oils and sweat residue. If tarnish has already set in, soak the jewelry in a solution of warm water and mild dish soap for about 15 minutes. A soft-bristled toothbrush can then be used gently to scrub dirt and tarnish from crevices before rinsing thoroughly and drying completely with a soft cloth.
Avoid using abrasive materials or harsh chemicals like bleach or ammonia, as they can damage the gold finish, especially on lower-karat or plated items. For deeply embedded tarnish or pieces with delicate gemstones, seeking professional cleaning is the most reliable way to restore the original luster without risking damage. Consistent and gentle cleaning prevents the buildup of corrosive compounds, preserving the jewelry’s shine for longer periods.