To understand the hallmarking system and the use of the word of the 'sterling', you first need to understand 'the science bit', as they say in the adverts! If silver jewellery were made of pure silver, it wouldn't last long, since silver, like other precious metals, is simply too soft. It has to be alloyed, or mixed, with other metals such as copper, which make it harder and more durable, whilst still keeping its malleability and beauty.