A hallmark must be struck on an item of silver, gold, platinum or, most, recently, palladium, by one of the four assay offices in the UK, in Birmingham, London, Edinburgh or Sheffield. Each assay office has a specific mark to signify which one has marked a piece of jewellery or silverware. I am registered with Birmingham Assay Office, whose symbol is an anchor.
A hallmark consists of this assay office mark, a unique mark to signify who has made the piece (the maker's mark) and a fineness mark. Pure metal is rarely used in jewellery: it is mixed with other metals to form an alloy, generally to make it stronger or better to work with. The fineness mark tells you the purity of the metal, for example sterling silver is 925. This is just the proportion out of 1000 that is pure silver. Other metals are marked in exactly the same way: 375 is 9carat gold, so 375 parts per 1000 is pure gold, 750 is 18carat, and so on. The shape this is written in signifies the metal - in the example of my hallmark below you can see the 925 in an oval, which shows it's silver. There is also an optional traditional fineness mark, which in this case is a lion for sterling silver.
|Emily Richard Jewellery's Hallmark from 2007, showing maker's mark, fineness mark, assay office mark, lion passant (traditional silver mark) and date letter 'h'|
Sometimes, an optional date letter is also stamped on. This signifies the year in which the item was hallmarked, and charts are available to decode the letters and work out which year each letter means. Obviously hallmarking has gone through several alphabets in several different fonts by now! So a "B" in one style will mean a different year to a "B" written in a different way, or in a different shaped outline. 2011 is the letter "m" in lower case, in a box with cut-off corners like the picture above.
The assay offices will test every item they are sent, to ensure the metal is what the maker says it is. They are an independant body, which has been marking metal to guarantee its quality for over 700 years.
Jewellery CAN be sold without a hallmark, but the seller is legally not allowed to sell it as gold, silver or platinum unless it has been marked by an assay office. So if it says it's gold, look for the hallmark to be sure! The only items that are exempt from this rule are items under 1gram for gold, 0.5grams for platinum or 7.78grams for silver.
A lot of my work in silver falls under the 7.78g limit, so it's not hallmarked (this would increase the price of the jewellery unnecessarily, as the assay offices charge a fee for marking items). I do have a 925 punch, which I can hammer into the surface of the metal to mark the fineness myself. I know it's sterling silver, and in most cases this will signify it really is silver, but it still doesn't actually prove anything as it was not marked at an assay office - I just did it myself! Most designer makers like myself will be honest, and won't try to sell you something that isn't genuine. But if you're in doubt, look for the official hallmark. It's the only way to guarantee what you're getting.