Why is silver getting dark? The question excites all owners of expensive jewelry made of this metal.
Silver is a noble metal with a fairly low reactivity to the most common oxidizing agents - water and air. However, in their presence, it nevertheless easily reacts with another substance - divalent sulfur. As a result of the reaction, Ag2S is formed - silver sulfide, which is a black substance. Under normal conditions, silver jewelry forms very slowly on silver jewelry. First, decorations begin to become covered with a slightly noticeable gray haze, then it turns into almost a black coating.
To understand why silver is getting dark, you need to understand what it is like as a chemical element capable of interacting with its surroundings. The main enemy of the noble color of silver is the supplier of sulfur H2S (hydrogen sulfide), which leads to its oxidation. Moreover, dry hydrogen sulfide does not cause such a reaction. This requires the presence of a moist environment. The reaction rate is able to increase the temperature, with the increase of which hydrogen sulfide corrosion can be accelerated several times. For example, if the temperature rises from 20 to 40 degrees, the corrosion rate will instantly increase 25 times!
Substances such as ozone, ammonia, hydrogen chloride, hydrogen sulfide, sulfur dioxide and free sulfur are freely present in the atmosphere. Depending on the concentration of these substances and air humidity, silver corrosion may intensify or weaken. Ag2S formed as a result of oxidation of the metal increases the coating layer of the product over time.
So, why is getting dark silver it becomes clear. But in addition to the air mentioned, hydrogen sulfide is also found in water. This is the next factor. With a high content of this compound in natural waters, they are used as therapeutic - sulfide (hydrogen sulfide) waters.
The main source of hydrogen sulfide emissions into the air is industrial enterprises that produce artificial fibers, oil refining and coke chemical enterprises, as well as almost all vehicles. In this case, it appears as a decomposition product of organic substances (waste).
What causes silver to darken under normal conditions if its contact with water is not allowed? Sulphide films are formed on jewels and upon contact or simply being close to 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 with food or medicine (streptocide, sulfadimezin, sulfazine, various ointments and other drugs. During metabolism, sulfur can recover to H2S and come to the surface of the skin with sweat, which comes in contact with rings, pendants and other favorite us jewelry.
Having studied all the enemies of silver, we now understand not only why silver is getting dark, but also realize that it is almost impossible to avoid such a darkening. Because we cannot live without air, water and are not able to reverse the reactions of our own body.
However, this is not all the reasons why silver is getting dark. Since in jewelry this metal is not used in its pure form, but only in alloys, copper is very often included in them. In air, it oxidizes 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. No other is given.
What can be done to extend the life of silver and maintain the original beauty of jewelry from it? It is necessary to ensure that the products do not overheat, are not in wet places. After wearing, they need to be wiped from skin secretions. It is also useful to periodically hand over jewelry for cleaning to jewelry stores or clean them yourself using soapy water with the addition of ammonia.