Why does silver darken?

Why is it getting darker? The question excites all owners of expensive jewelry from this metal.

Silver is a noble metal with a low enoughreactivity to the action of the most common oxidants - water and air. However, in their presence, however, it easily reacts with one more substance - divalent sulfur. As a result of the reaction, Ag2S - silver sulfide is formed, which is a substance of black color. Under normal conditions on silver jewelry, the sulphide is formed very slowly. At first the decorations begin to become covered with a slightly noticeable gray haze, then it turns almost into a black raid.

To understand why silver is getting dark, you needto understand what it is like as a chemical element, capable of interacting with its environment. The main enemy of the noble color of silver is the supplier of sulfur H2S (hydrogen sulphide), which leads to its oxidation. And dry hydrogen sulphide does not cause such a reaction. This requires the presence of a moist environment. The reaction rate is capable of increasing the temperature, with the increase of which hydrogen sulphide corrosion can accelerate at times. For example, if the temperature rises from 20 to 40 degrees, the corrosion rate will instantly increase by 25 times!

In the atmosphere are freely present such substances,As ozone, ammonia, hydrogen chloride, hydrogen sulphide, sulfur dioxide and free sulfur. Depending on the concentration of these substances and the humidity of the air, silver corrosion can be intensified or weakened. The resulting Ag2S metal oxidation over time increases the coating layer of the product.

So, why the darkening of the silver becomes clear. But in addition to the air, hydrogen sulphide is also present in the water. This is the next factor. With a high content of this compound in natural waters, they are used as therapeutic - sulfide (hydrogen sulphide) waters.

The main source of hydrogen sulfide release into the air -industrial enterprises that produce man-made fibers, oil refineries and coke-chemical plants, as well as virtually all transportation. In this case, it appears as a decomposition product of organic substances (waste).

What darkens the silver under normal conditions, ifdo not allow it to come into contact with water? Sulfide films are formed on jewelry and on contact or simply by the presence of materials of organic origin, for example, rubber, compounds, plastics.

Do not forget that our body itselfis capable of producing sulfur. It enters the body from the outside with food or medicine (streptocid, sulfadimezinom, sulfazinom, various ointments and other drugs.In the course of metabolism, sulfur is able to recover to H2S and go to the surface of the skin with sweat, which contacts with rings, pendants and other loved ones us ornaments.

Having studied all the enemies of silver, we now understandonly, why the silver darkens, but we also realize that it is practically impossible to avoid such a darkening. Because we can not live without air, water and can not reverse the reactions of our own organism.

However, this is not all the reasons why it gets darkersilver. As in jewelry, this metal is not used in pure form, but only in alloys, very often copper is included in them. In air, it is oxidized to Cu2O, acquiring a reddish hue. If the product is not covered with a protective layer, for example, radium or palladium, they will stain at all times. The other is not given.

What can be done to extend the life of silver andto maintain the original beauty of jewelry from it? It must be ensured that the products do not overheat, they are not in wet places. After wearing them you need to wipe from dermal secretions. And it is also useful to periodically take jewelry for cleaning in jewelry stores or clean them yourself with the help of soapy water with the addition of ammonia.