Gold is one of the most coveted of the precious metals; much loved for its lustrous appearance and soft quality. Gold rings are a favorite jewelry item, however, it's not uncommon to encounter a blackish ring forming on the skin beneath the ring. This sometimes prompts questions concerning the purity of the gold, but there are actually several other factors that may be responsible for the black tint.
Properties of Gold
Gold is a malleable and ductile metal, making it easy to manipulate into thin sheets or coiled wires. It is also very soft. On the Mohs scale of hardness, it has a value of 2 to 2.5, while diamond, the hardest material in the world, has a value of 10. Gold is also chemically inert and does not corrode or tarnish. It has a deep yellow color and is very reflective, which helps it retain its brightness. Gold is also very scarce.
Gold in Jewelry
It is gold's malleability, ductility and reflectivity that make it suitable to mold into jewelry. Its scarcity makes it expensive. Gold's softness means most jewelers have to mix it with other metals like silver, copper and nickel to make it hard and more resistant to damage. The purity of gold is measured in karats. One karat is 4.166 per cent gold by weight; 24 karats is 100 % pure gold. Jewelry is typically 14- 18 karats or less and 14 karat gold is really 58 percent gold and 42 percent other metals. It's these other metals in found in gold jewelry that often cause skin blackening.
Sulfur, chlorine and other elements in the atmosphere react with copper, silver or nickel in the gold jewelry and cause it to corrode. This results in gold rings and other pieces of gold jewelry turning black and in turn blacken the skin. This has been known to happen in coastal regions where there is a lot of salt or chlorine in the atmosphere.
Wear and Tear
Often times gold jewelry is really only gold-plated. Being soft, the gold-plating wears off from abrasion, and the metal underneath becomes exposed. This metal then reacts with the skin and the atmosphere and causes blackening. The abrasion can be a result of interactions with chemicals or harsh cleansers.
Make-up can also be a cause of wear and tear in jewelry. Make-up consists of minute abrasive particles that can scratch jewelry and expose the base metal or generate fine dust that looks black.
Sweat and acids released by the body when perspiring can react with gold alloy and discolor jewelry.
Often rhodium is used to plate jewelry to prevent chemical reactions in the metal. Care should be taken when using make-up. It is advisable to remove gold jewelry while applying cosmetics and washing hands to rid them of make-up before putting on the jewelry again. It is also advisable to wash gold jewelry with an appropriate cleaning solution to remove sweat and dirt that may accumulate.