A dark discoloration on gold jewelry, known as tarnish, is a frequent phenomenon with real gold items. This blackening is not a sign of poor quality or fakery. The process is a chemical reaction that occurs when the metals alloyed with pure gold react to common substances in the environment. Understanding the underlying metallic composition and external agents is the first step toward preventing and solving the problem.
The Role of Alloys in Gold Discoloration
Pure gold (24-karat) is nearly 100% gold and does not tarnish because it is highly resistant to chemical reactions. However, pure gold is too soft for everyday use. It must be combined with other metals to create an alloy that provides strength and durability, which makes the jewelry susceptible to blackening. The karat rating indicates the proportion of pure gold in the mixture; for example, 14-karat gold is 58.3% gold, with the remaining 41.7% composed of alloying metals.
The metals most frequently mixed with gold are copper, silver, and occasionally nickel or zinc, which increase the hardness of the final piece. Lower-karat gold, such as 10-karat or 14-karat, is more prone to discoloration due to the higher percentage of these reactive metals. The gold itself remains pristine, but the non-gold metals in the alloy are the components that chemically react with external agents.
Specific Chemical Causes of Blackening
The black film on gold jewelry results from alloyed metals reacting with various chemical compounds to form dark surface layers. The most common cause is a reaction with sulfur compounds, which are prevalent in the environment. These substances, such as hydrogen sulfide gas in the air, cause the silver and copper in the alloy to form silver sulfide or copper sulfide, which appears as dark tarnish.
Contact with chlorine, often found in household cleaning products and swimming pool water, is another frequent cause of blackening. Chlorine reacts with the alloy metals to create metal chlorides, which manifest as a dark surface layer. Furthermore, a person’s body chemistry, including sweat and natural body oils, can accelerate these reactions because perspiration contains salts and fatty acids. Cosmetics, lotions, and perfumes also contain chemical components that interact with the alloy metals, leading to the formation of dark compounds.
Safe Methods for Cleaning Tarnished Gold
For pieces with light tarnish or routine buildup of dirt and oils, the simplest cleaning method involves warm water and a small amount of mild dish soap. The jewelry should soak in this solution for 10 to 15 minutes to loosen surface grime. After soaking, use a soft-bristled toothbrush to gently brush the surface, focusing on crevices where dirt accumulates.
It is important to rinse the piece thoroughly under clean, lukewarm running water to remove all soap residue, which could dull the shine. The gold should then be dried completely using a soft, lint-free cloth, as remaining moisture encourages future tarnishing. For heavy or stubborn tarnish, seek professional cleaning services. Jewelers have specialized equipment, like ultrasonic cleaners, that can safely restore the luster without damaging the metal or accompanying gemstones.
Preventing Future Discoloration
Preventing the chemical reactions that cause blackening requires mindful habits regarding when and how gold jewelry is worn and stored. Since chlorine and sulfur compounds are the primary culprits, remove gold items before swimming (especially in chlorinated pools) or using strong household cleaners. Jewelry should also be taken off before exercising, as sweat contains compounds that accelerate the tarnishing process.
A simple preventative step is to apply all cosmetics, lotions, and perfumes and allow them to dry completely before putting on gold jewelry. For storage, keep jewelry in a cool, dry environment because moisture and humidity encourage tarnish formation. Storing pieces in a closed container with anti-tarnish strips or silica gel packets can help absorb airborne moisture and corrosive gases, slowing the darkening reaction.