Our silver is called 925 Sterling Silver and is the most common alloy in jewellery. It means that 92.5 % is silver and the rest is copper.
When Silver turn black:
It is a well known fact that silver often turns black and the reason is the presence of sulphur. Sulphur occur in many context; in the air, on the skin, in food, on painted surfaces, in textile fabric, plastics, cigarette smoke, fossil fuel, rubber bands, etc. When the silver comes in contact with the sulphur, there is a chemical reaction called Silver sulphides (AgS) and it shows as a black film on the silver surface. Some people secrets sulphur on the skin. In some cases it depends on that the person take medicines.