Precious metals used in jewellery manufacture are always used as an alloy. The precious metal must be mixed with other elements to give it the necessary properties (such as flexibility) to produce a desirable and durable article.
Hallmarking was originally introduced in 1300 by a Statute of Edward I and is one of the earliest forms of consumer protection.
Therefore, all items being sold as gold, silver, or platinum in the UK must be hallmarked to confirm that they meet the legal standard. This cannot be done by the manufacturer or importer; goods must be submitted to one of the four UK Assay Offices, or an Assay Office belonging to the International Convention.
The only items which are exempt are those which are under the legal weight threshold, or if they are too delicate to mark.
The legal weight threshold is 1 gram for gold, 0.5 grams for platinum and 7.78 grams for silver
Examples of UK hallmarks are shown in the image supplied, and typically contain:
Sponsor's (formerly maker's) mark; (F.L.J. shown)
Standard of fineness (parts out of 1000) e.g. Crown 375 or Lion Passant 925 (shown)
Assay Office where the article was tested and marked (Anchor for Birmingham shown)
Year in which the article was tested and marked (e.g. n for 2012)
Other marks may also appear e.g. for The Queens Jubilee