Oxidization of Gold and silver
Published on Nov 30, 2019
What is oxidization?
‘Oxidization/Oxidation of metal’, commonly known as ‘Tarnishing’, is the slight corrosion of the metal surface, causing the discoloration or blackening of a piece of jewelry. This is a natural process where the metal interacts with sulphur-bearing pollutants in the environment, to create a sulphide layer over its surface, resulting in the visible discoloration. This is an ongoing problem for jewellers, particularly for silver and low carat gold articles.
How does Gold and silver get tarnished?
Gold is one of the least reactive elements. Pure gold does not combine easily with oxygen, so it stays shiny, it does not rust or tarnish. However, pure gold or 24 carat gold is too soft to be used in jewelry, so it is usually alloyed with proportions of other base metals, usually silver or copper to make it harder. It is these other base metals alloyed with gold that react with oxygen, sulphur and moisture, eventually tarnishing the gold jewelry.
Similarly, silver jewelry tarnishes due to contact with sulphur compounds present in the atmosphere, forming a dark coating over the metal’s surface that is undesirable to look at.
Other causes of oxidization
Cosmetics often contain chemical compounds, which when come in contact with the jewelry metal, wear or rub off very minute particles of metal which appear as jet black dust. To prevent this, cosmetics which contain zinc oxide, titanium dioxide and ferric oxide should be avoided. It is also recommended that rings and other metal jewelry should be removed while applying cosmetics.
Our skin on which the jewelry lies, is provided with thousands of perspiration glands. The body sweat, which is mostly fat and fatty acids, is enough to cause corrosion of the jewelry metal when aided with warmth and free access to air. Rings containing silver and copper alloys corrode readily on the skin if enough salt is present.
Soap, detergent, wax, polish and cosmetic creams may build up under a ring, resulting in the burning sensation and redness of the skin. To prevent this, one should remove all the jewelry before using soap or detergent.
Oxidation is a natural process and not a manufacturer’s defect. The amount of oxidation that occurs on an individual piece of jewelry depends on many factors including how detailed the jewelry is combined with the habits and care of the person who wears the jewelry. As long as the jewelry is certified with a hallmark on it, there is no need to doubt on the quality/purity of the metal.