In short, silver reacts with sulphur oxides present in the air (e.g. hydrogen sulphide) and a black substance is created called silver sulphide.
In order for silver to be strong enough to work with and to have longevity as a piece of jewellery, copper is added in its manufacturing process.
Sterling silver has a purity of 92.5% silver (hence the 925 stamp in the hallmark). This means that 7.5% of the alloy is copper and other metals like zinc.
Next week I am heading to Market Rasen Racecourse for the 34th Annual Shopping Extravagana to raise money for Blood Cancer UK!