Silver rusts due to oxidation and the color will be black.
Silver is an unstable element and can easily interact chemically with sulfur, resulting in blackening. The human body sweat contains a lot of sulfur, and silver jewelry in contact, it will happen. Moreover, if a person is in some polluted environment, acidic gases, hydrogen sulfide, nitric oxide and other compounds in the air are more, it will also lead to silver jewelry black.
Moreover, the discoloration of silver jewelry may also be caused by the serious insufficiency of the ingredients. Even if you exclude the above cases, under normal circumstances, the surface of silver jewelry will oxidize after wearing it for about half a year, and the color will become dull and lose its luster.
Silver classification:
One, silver: silver content of not less than 990 kilograms called silver. Because too soft, not easy to cast into the desired jewelry shape, and easy to wear and oxidation black. Therefore, it is not suitable for jewelry production.
Two, silver grain: silver content of not less than 925 kilograms of silver grain. Also known as "925 silver", grain silver is usually 92.5% silver mixed with 7.5% copper. As a result of copper, its manufactured products in the polished luster, than silver dazzling beautiful, and therefore often used as jewelry materials and silverware.
In order to increase the gloss of 925 silver jewelry and reduce its oxidation some manufacturers will also be plated with a layer of white gold. These products are commonly known in the industry as real gold and silver products.
Extended information
Silver is one of the metals known and utilized in ancient times, is an important precious metal. Silver exists in nature as a single substance, but the vast majority of it exists in the form of a chemical compound in silver ores.
Silver physical and chemical properties are more stable, thermal and electrical conductivity is very good, soft, rich ductility. Its reflectivity is extremely high, up to 99% or more. There are many important uses. The most important compound of silver is silver nitrate. In medicine, commonly used silver nitrate aqueous solution for eye drops.
Sterling silver is a beautiful silvery-white metal that is very malleable and has the highest electrical and thermal conductivity of any metal. Silver is commonly used to make extremely sensitive components of physical instruments, all kinds of automated devices, rockets, submarines, computers, nuclear devices, and communication systems, all of which have a large number of contact points made of silver.
During the period of use, each contact has to work millions of times, and must be wear-resistant and reliable to withstand the rigors of the work, silver can fully meet the requirements of all kinds of requirements. If the silver in the addition of rare earth elements, performance is even better. With this kind of silver with rare earth elements produced by the contact point, life can be extended several times.
Baidu Encyclopedia-Silver