Most gold carries some kind of hallmark or "assay mark," the purpose of which is to show that the piece has reached a recognised standard of purity so that it can be legally retailed. This standard of purity can be expressed in two ways, either as parts per thousand or as carats (sometimes spelt "carats.") Caratage is a standard expressed as parts per 24. Only four standards of gold are widely used, so you should have no difficulty recognising their respective hallmarks when you see them. However, you will need a jeweller's loupe, as some gold hallmarks can be tiny.
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Things you need
- Jeweller's loupe
Check over a piece carefully to see if it has any hallmarks, using a jeweller's loupe to inspect any unusual marks. The marks you are looking for will be either impressed into the gold or laser-etched; they won't be scratched in by hand. On necklaces, first check in the area of the clasp, then try some of the individual links. With trinket boxes, look inside; there will probably be two hallmarks, on the interior of the lid and on the body of the box. On pocket watches, the hallmarks should be on the inner-facing surface of the outer casing. With wristwatches, you will probably need to remove the backing to find the hallmarks, but it's also worth checking the buckle of a leather watchstrap or the links of a metal watchstrap.
Look at the mark you have found for the letters "ct", "kt" or "K" standing for "carat" or "carat." The four commonly used standards of purity are 9 (the minimum in the United Kingdom,) 10 (the mininum in the United States,) 14 and 18 carats. You should therefore hope to see one of four stamps - "9 ct," "10 ct," "14 ct" or "18 ct" If you don't see a mark expressed in carats, go on to Step 3.
Inspect the mark to see if it is one of four likely three-digit numbers -- "375," "417," "585" or "750." These are the four common standards of purity -- 9, 10, 14 and 18 carats -- expressed as parts per thousand. Some pieces will bear both of the marks mentioned in Steps 2 and 3, while some will have only one, but either mark is a certain sign of genuine as opposed to plated gold.
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