Your jewellery is designed to be wearable and unique. When treated with care, your jewellery should bring you many, many years of joy.
Sterling silver can tarnish over time, turning dull and discoloured. This is a result of the intrinsic properties of the metal and is entirely normal. 9 carat gold is less susceptible though not immune, and the highest carats of gold do not tarnish. The best way to prevent your jewellery tarnishing is to wear it regularly - the friction from your clothes and daily movements can help to stop oxides building up on the surface. When it is not being worn, keep your jewellery safely in the box in which you received it, or another jewellery box or pouch. Take care to ensure delicate items are not allowed to be damaged by the heavier pieces you might have in your collection.
If you do find your jewellery has tarnished, it is easy to clean. An effective, non-toxic way to clean tarnished jewellery at home is by adding a piece of kitchen foil, a generous spoonful of bicarbonate of soda, and your jewellery item to a heat-proof, non-metallic bowl. Cover with boiling water and let it sit for a while. Once your piece is looking fresh and clean again, give it a careful brush using a soft-bristled brush (an old, clean toothbrush is ideal) and a spot of liquid detergent, rinse, and you're done! Alternatively, a careful buff with a soft polishing cloth should bring your pieces back to full shine again.