Why does silver darken?

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

Silver is a noble metal with a sufficiently low reactivity 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 sulphide is formed, which is a substance of black color. Under normal conditions on silver jewelry, sulphide is formed very slowly. At first the decorations begin to be covered with a slightly noticeable gray haze, then it turns almost into a black raid.

In order to understand why silver is getting dark, one must understand what it is like as a chemical element capable of interacting with its surrounding mediums. 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, at 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 instantly increases by 25 times!

In the atmosphere, free substances such as ozone, ammonia, hydrogen chloride, hydrogen sulfide, sulfur dioxide and free sulfur are freely present. Depending on the concentration of these substances and the humidity of the air, the corrosion of silver can be intensified or weakened. The resulting oxidation of the metal Ag2S 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 - sulphide (hydrogen sulfide) water.

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

What makes the silver darken under normal conditions, if you do not allow its 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 itself is capable of producing sulfur. It enters the body from the outside, along with food or medicine (streptocide, sulfadimezinom, sulfazinom, various ointments and other drugs.In the course of metabolism, sulfur is able to recover to H2S and leave on 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 understand not only why silver is getting dark, but we also realize that it is almost impossible to avoid such darkening. Because we can not live without air, water and are not able to reverse the reactions of our own organism.

However, this is not all the reasons why silver is getting darker. Since 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 always blacken. The other is not given.

What can be done to extend the life of silver and 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. 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.