Silver - A very popular and regularly used metal for jewellery. Often considered more "modern" than gold and considerably cheaper.
Silver comes in various degrees of purity but "sterling" silver is the degree of purity desirable and sought after for jewellery.
Sterling silver is a term used in the industry for high quality silver. "Fine" or "pure" silver is much too soft to use in most jewellery applications so it is combined with other metals/alloys to add strength and durability. The most popular and widely used alloy is copper, 7.5% is added and hence you get 92.5% of fine silver. This is why you often see .925 marked on your jewellery.
.925 silver is nickel free.
Silver is a precious metal that can and unfortunately will, tarnish. Most, but not all, modern silver jewellery is rhodium plated and this usually helps prevent tarnishing. You should however, expect a certain amount of tarnish as normal. Chains especially, are susceptible to tarnish. Tarnish starts off as a dull yellowish tinge and ends up black.
To help prevent tarnish you should keep your jewellery carefully protected when you are not wearing it, perhaps in the packaging in which it is supplied and in as dry an environment as possible. If cleaning does become necessary and the tarnish is light, try warm water and a soap solution and a soft toothbrush. Be sure to rinse and dry the item thoroughly. Chains are most easily cleaned by dipping in a proprietary silver dip. You should never dip jewellery that contains pearls or "soft" stones. If you need to try and clean settings containing this type of stone, then try using a cotton wool bud soaked in silver dip. Be sure to rinse and dry carefully. You can find out more about silver from these sites: The Silver Institute - Facts about silver. The Silver Institute - The History of Silver. Wikipedia - The chemical properties of silver | 
