The question of whether gold turns brown is common, and the straightforward answer is both yes and no. Pure gold (24-karat gold) is a noble metal and does not chemically react with the environment to cause discoloration. Therefore, 24-karat gold will not turn brown or black under normal circumstances. However, almost all gold jewelry contains a mixture of metals, and these other components are susceptible to tarnishing. The discoloration observed is a surface chemical reaction happening to the non-gold metals within the alloy.
The Unique Chemistry of Pure Gold
Pure gold is impervious to the chemical changes that cause tarnish because it is classified as a noble metal. This stability means it resists bonding with common atmospheric elements like oxygen and sulfur. Gold’s chemical symbol, Au, represents an element with a highly stable electron configuration.
The outer electrons of a gold atom are tightly bound and less available for chemical reactions, preventing the oxidation process that degrades most other metals. This inertness allows pure gold to retain its brilliant color and luster even after centuries of exposure.
The Real Cause of Discoloration
Jewelry is rarely made of 24-karat gold because the metal is too soft for daily wear. To increase durability, gold is mixed with other metals, creating an alloy, and these additive metals cause the brown or black discoloration. The karat system indicates the proportion of pure gold; for example, 14-karat gold contains 14 parts gold and 10 parts of other metals.
The reactive metals most commonly alloyed with gold are copper and silver, though zinc and nickel may also be present. These metals readily react with sulfur compounds in the environment, forming dark chemical layers called metal sulfides.
Sulfur is found in many everyday items and environmental factors, including air pollution, rubber products, and human sweat. When copper and silver in the alloy react with these sulfur-containing gases, they form copper sulfide or silver sulfide. This dark layer is the tarnish that makes gold jewelry appear brown or black. Moisture and high humidity accelerate this chemical reaction, causing lower-karat gold (which has a higher percentage of reactive metals) to tarnish more quickly.
Preventing and Reversing the Change
The most effective way to address discoloration is to minimize your jewelry’s exposure to reactive agents. Remove gold jewelry before swimming, especially in chlorinated water, as chlorine attacks alloyed metals. Lotions, perfumes, hairspray, and household cleaning agents also accelerate tarnishing, so jewelry should be the last thing you put on and the first thing you take off.
Proper storage slows the chemical process of tarnish formation. Jewelry should be kept in a cool, dry place, ideally in an airtight container or an anti-tarnish bag to limit exposure to moisture and sulfur compounds. Wiping pieces with a soft cloth after each wear removes skin oils and residues that contribute to tarnish build-up.
If discoloration has occurred, you can safely reverse it with gentle cleaning methods. A simple and effective home remedy involves soaking the jewelry in a solution of warm water mixed with mild dish soap for 10 to 20 minutes. A soft-bristled toothbrush can then be used to gently scrub away accumulated tarnish. After scrubbing, the piece should be thoroughly rinsed in warm water and dried completely with a soft, lint-free cloth.