Alloy metal is a material made by combining two or more metallic elements, or a metal with a non-metallic element, often to enhance its strength or appearance. When people wear jewelry containing certain alloys, they often encounter a harmless yet annoying phenomenon: a greenish discoloration on the skin beneath the metal. This discoloration frequently leads to the mistaken belief that the item is counterfeit or of poor quality. Understanding the science behind this predictable chemical reaction can help prevent the staining from occurring.
The Chemical Reaction Behind the Green Stain
The root cause of the green stain is a natural chemical process known as oxidation, which involves the copper content present in many common alloys. Copper is the primary metal responsible, reacting readily when exposed to moisture and the chemical compounds found on human skin. This reaction is accelerated by external factors such as sweat (which contains salts) and the natural oils and acids that the skin produces.
When copper atoms on the alloy surface contact these substances, they lose electrons and form new compounds called copper salts. These copper salts, such as copper chloride or copper carbonate, are naturally blue-green in color. The resulting colored substance then transfers from the metal surface onto the skin through friction and moisture.
Identifying the Alloys Most Likely to Cause Discoloration
The alloys most likely to cause this reaction are those with a high percentage of copper, even if copper is not the primary metal. Brass (an alloy of copper and zinc) and bronze (traditionally copper and tin) are two of the most common culprits. These materials are often used in costume jewelry and plated pieces, causing a reaction when the outer plating wears away.
More precious alloys are not immune, as they also rely on copper for durability. Sterling silver contains 92.5% silver and typically 7.5% copper, which can lead to a mild green or black reaction. Lower-karat gold (such as 10K or 14K) also contains significant copper to increase hardness, occasionally triggering a reaction depending on the wearer’s body chemistry.
To avoid the issue entirely, non-reactive metals are considered safe alternatives:
- Stainless steel
- Titanium
- Platinum
- High-karat gold (18K or 24K)
Stopping and Preventing the Green Reaction
Preventing the green stain involves creating a barrier between the reactive metal and the skin, and minimizing exposure to corrosive substances. A simple method is to apply a thin, clear coating to the parts of the jewelry that touch the skin. Products like clear nail polish or specialized commercial jewelry sealants create an invisible, protective layer. This barrier must be reapplied periodically, especially if the coating begins to chip or wear off.
Keeping the jewelry clean and dry is another important step. After each wear, wiping the piece with a soft cloth removes corrosive residues like sweat, oil, and lotion before they accelerate oxidation. Proper storage in a dry environment, such as an airtight container or a jewelry box with anti-tarnish strips, helps reduce exposure to air and humidity.
Wearer habits also play a large role in mitigating discoloration. It is helpful to remove the jewelry before engaging in activities that cause heavy sweating (such as exercise), or before swimming or showering. Additionally, lotions, perfumes, and other cosmetic products should be allowed to fully absorb and dry on the skin before the jewelry is put on, as these chemicals can promote the reaction.