Often, the owners of silver this attack is referred to the negative influence of evil forces. It is believed that the unexpected blackening of jewelry associated with building damage or disorder in the body. Although this superstitious fear is not so unfounded, there is still more down to earth explanation of this fact, and from the point of view of the laws of chemistry.
The blackening of silver causes oxidation of the metal in the interaction with sulfur. This chemical reaction creates sulphides that are chemicals grey-black color, which covers jewellery and other silverware.
Sulfur can enter the product of human sweat, water, cosmetics, and even air. This explains the fact that dark can even items that are practically not exposed to touch, for example, decorative.
Silverware, as a rule, contain not only the metal but also copper. This is because silver is very soft and easy to deformation, and the addition of copper makes the items more durable. Copper also undergoes oxidation and causes the formation of sulphides even more, which in turn leads to a darkening and silver.
It is known that from jewelry, to a lesser extent prone to darkening earrings. This is due to the absence of sweat glands in the ear lobes. Often darken chains and pendants, at least – rings, however, they may not darken due to perspiration, and from contact with various chemicals, for example when cooking or washing the dishes, cleaning the house.
The oxidation state of silver is dependent on purities: less susceptible to darkening of the product 999 (high) samples, more - 875. Cutlery, as a rule, contain more copper, so oxidize is stronger and can almost completely black, so they require systematic care.
Human sweat can not only cause blackening of the silver, but on the contrary, be the cause of his highlights. Religious-minded people associate it with the bright aura of a person, but it also has a scientific explanation: in addition to sulfur sweat contains nitrogen, high content of which reacts with the silver and causes the lightening decorations.