Diamonds, pearls and fine jewels are often passed on through families for generations but these treasured pieces require meticulous and constant care in order to keep them in top shape. 'It is most important to take care of jewels to prevent them from oxidising, which can lead to change of colour and other damages,' a spokesman for Spanish jewellery company ARTC said. The most popular jewels can be categorised into three major types - diamonds, pearls and other gemstones - and each type requires a different method of cleaning. A diamond, for example, requires relatively simple care. As the hardest gem with a Mohs scale of hardness of 10, diamonds are not easily scratched. As such, diamond-studded jewellery left alone has a low chance of clarity loss. Daily wear of such jewellery is also not a problem. However, each time the piece is worn it should be cleaned with clear water or alcohol and dried off with a towel. On the other hand, pearls are much more delicate and require more attention when it comes to looking after them. According to Mikimoto, known for its fine pearl pieces, this type of organic gemstone is 'vulnerable to acid, alkaline and different humidity levels', so even if left in a jewellery box untouched, the pearls may still discolour, especially with the seasonal high humidity in Hong Kong. Pearls are made up of layers of calcium carbonate and are not as hard as diamonds with a Mohs score of 3.5 to 4.5. So it is advisable to put these jewels in individual boxes to avoid them being scratched by other jewellery pieces or materials, which will result in a loss of lustre. It is also highly recommended to store pearls away from the sunlight. If such jewellery is left in direct sunlight for a long time, the lustre may be damaged and the top coat shine will be lost. Pearls don't fracture easily but can easily change colour when they come into contact with certain chemical acids. 'If you are wearing a pearl necklace and put perfume or hair spray on; there is a great chance of discolouring t*he pearls' said Joyce Tong, the assistant marketing manager of Mikimoto Pearl Jewellery (HK). When cleaning pearl jewellery, the piece must be wiped off carefully with a soft silicon cloth, with a bit of pearl cleanser added if desired. It is important to know that pearls must never be cleaned with water or alcohol. Like pearls, the clarity of other types of gemstones clarity may be marred when put in contact with chemicals and their surfaces can be easily scratched. An ARTC spokesman suggested cleaning them with a toothbrush and detergent. Diamonds, pearls and most gems may be cleaned with an electrolytic cleaning machine. But pearls should be put in for only a short while and gems like emeralds and opals should not be cleaned by this method.