Gold is one of the most coveted metals in the world, much loved for its lustrous appearance, and gold rings are a favourite jewellery item. However, it is not uncommon to notice a blackening of the skin underneath the ring. This has prompted people to question the purity of the gold, but there are really several other factors that are responsible for this.
Properties of Gold
Gold is a malleable and ductile metal, which means it can be easily beaten into thin sheets or drawn into 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 colour and is very reflective, which helps it retain its brightness. Gold is also very scarce.
Gold in Jewelery
It is gold's malleability, ductility and and reflectivity that make it suitable to mould into jewellery. Its scarcity makes it expensive. Gold's softness means most jewellers 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 carats. One carat is 4.166 per cent gold by weight. 24 carat is 100 per cent pure gold. Jewellery is usually 14 or 18 carats or less. 14 carat gold is really 58 per cent gold and 42 per cent other metals. These other metals in gold jewellery often cause skin blackening.
The sulphur, chlorine and other elements in the atmosphere react with the copper, silver or nickel in the gold jewellery and cause it to corrode. This results in gold rings and other pieces of gold jewellery turning black and in turn blackening the skin. This has been known to happen in coastal regions where there is a lot of salt and therefore chlorine in the atmosphere.
Wear and Tear
Often gold rings and other pieces of jewellery are really gold-plated. Gold being soft, the plating wears off due to abrasion, and the metal underneath is then exposed. This metal then reacts with the skin and the atmosphere and causes blackening.The abrasion could be caused by chemicals or harsh cleansers. Sometimes it is the fine metal dust that has been scrubbed off that appears black.
Make-up can also be a cause of wear and tear in jewelery. Make-up consists of minute abrasive particles that can scratch jewelery and expose the base metal or generate fine dust that looks black.
Sweat and acids released by the body when perspiring could react with the gold alloy and discolour jewellery.
Often rhodium is used to plate jewellery to prevent chemical reactions in the metal. Care should be taken when using make-up. It is advisable to remove gold jewellery while applying cosmetics and washing hands well to rid them of make-up before putting on the jewellery again. It is also advisable to wash gold jewelery with an appropriate cleaning solution to remove sweat and dirt that may have settled on it.