I had my tour of the Assay office is London this morning. Hallmarking is one of the oldest forms of consumer protection. If an item is hallmarked, you have a guarantee of the precious metal content of that item. If you see silver with just "925" stamped on it, that is not a hallmark. It must have the hallmarks of the Assay Office. There are international hallmarks and country specific hallmarks. I usually use the UK hallmark, since it is internationally recognised. Not all items have to be hallmarked, for each metal there is a weight limit above which an item has to be hallmarked in order to be sold as that metal. For silver the limit is just under 8 grams, so most of my earrings are not hallmarked, since they are so small.
When I registered with the Assay Office so I could get my items hallmarked, they gave me a time and day for a tour of the office. That was this morning, so I guess they must give a lot of tours!! But I was the only person, so private tour, great! They showed me the whole process, from the package arriving to being laser or hand punched or tested. They don't test every single item in great detail. Basically all items (or a percentage of items if it's for a big client who sends in 3,000 of the same necklace, for example) are xrayed to see if they are silver/gold/sterling silver/etc. If it's clear from the xray then they get hand punched or laser marked depending on what the client asked for. If it's not clear, then they run tests to determine, for example, the carat of gold. It was also interesting how they test scrap. In jewellery, no scrap is waste. You can sell your scrap back to companies like Cooksons and then they melt the scraps together (silver together, and gold together) and then the Assay office can test them with their spectrometer to see exactly what part of the scrap is pure gold or silver (or platinum). It was quite interesting and I even got a dvd about the history of Goldsmith's Hall. You can find more information on their website as well: http://www.thegoldsmiths.co.uk/assayoffice/