Hallmarking in the UK is one of the oldest 'quality control' procedures, first established around 1300. Items sold as platinum, gold or silver in the UK must have a full set of hallmarks, proving that the metal is as claimed. Hallmarks generally consist of 3 stamps which are made by the various Assay Offices around the UK. Every item made of these materials must be sent to an Assay Office for testing, and dependant upon the outcome are then marked with the appropriate stamps. More information on all the marks used can be found on the Assay Office web sites, but its worth noting that any item marked with only the numbers 925 has not been hallmarked. Also the size of the marks vary greatly, and on small delicate pieces on jewellery its often necessarily to use a magnifying glass to see the marks in any detail. Almost all precious metals used in jewellery manufacture are mixed with other metals to make them more hardwearing and more workable and there are several recognized purities of precious metals: Platinum is hallmarked as 850, 900, 950 and 999 purities. Platinum is an extremely expensive metal and hallmarks are required at a weight of 0.5g and above. (Just about any jewellery item will weigh more than this.) Gold is hallmarked as 9ct, 14ct, 18ct 22ct, and less commonly as 990 and 999 (very high purity). For jewellery, items are usually 9ct - 18ct as the higher purities are extremely soft and not suitable for items that will be worn. Gold is an expensive metal and hallmarks are required at a weight of 1g (almost any jewellery item will weigh more than this) Silver is hallmarked at 800 and 925 purities. There are also higher purities, not suitable for making jewellery, as it is too soft. The most common purity is 925, and this is known as sterling silver. It's 92.5% silver and 7.5% copper and other metals. Silver is a less expensive metal and hallmarks are required at 7.88 grams. As a rough guide, most earrings, small rings and finer chain necklaces and chain bracelets will be under the legal limit for hallmarking. Items that are plated in a precious metal do not require hallmarks unless the underlying metal is also precious. For example there is currently a growing trend for brands to make collections in gold plated silver. Often a silver hallmark is applied to the item before plating, but in this case it's worth asking the retailer to explain the composition of the piece before buying, and if they are unsure the ask them to contact the manufacturer.