Jewellery testing in the 21st Century
Published: 25th March 2019
Sheffield Assay Office uses the latest X-ray Fluorescence (XRF) measuring technology to determine the precious metal content of articles received for hallmarking.
Until around 15 years ago, tiny samples of metal had to be physically removed from the jewellery and sent to the laboratory for analysis by fire assay (for gold), potentiometric titration (silver) and ICP-OES (platinum and palladium).
These traditional reference methods of assaying are still used occasionally to assure the accuracy of our instruments but XRF is a much more environmentally friendly process, with no need for acids, lead foil or furnaces.
XRF instruments determine the chemistry of a sample by measuring the fluorescent (or secondary) X-ray emitted from a sample when it is excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays ("a fingerprint") that is unique for that specific element. By measuring the intensity of these individual spectral peaks, the composition of the alloy can be calculated.
This technique tells us the fineness of the metal quickly and with a high degree of accuracy. Our test method is independently accredited by UKAS to the ISO/IEC 17025 international standard, which sets out strict validation criteria. Certified reference materials are used to calibrate the instruments and checks are also made by the Queen’s Assay Master of the Royal Mint on a regular basis. Our modern instruments are fitted with a silicon drift detector and digital pulse processor, which gives a resolution of < 160 eV and a very high count rate. As a result, accuracy is much greater and measuring times shorter than when using cheaper, hand-held instruments.
Much of the jewellery submitted for hallmarking by our customers nowadays is imported and ready for immediate sale, so is received in a highly polished state. This non-destructive technique is ideally suited for avoiding damage and enables us to offer faster turnaround times to our customers, such as our 1-hour hallmarking service.
By combining state of the art technology with 240 years’ experience, the Sheffield Assay Office offers a high quality assaying and hallmarking service which aims to exceed the expectations of our customers, and give peace of mind for anyone buying precious metal jewellery.
The Sheffield Assay Office was established in 1773, under an Act of Parliament and today the company assays and hallmarks the precious metals - silver, gold, platinum and palladium. Sheffield Assay Office is one of only four UK assay offices who all work to uphold the Hallmarking Act of 1973 and continue to ensure consumer protection for customers purchasing precious metals.
To find out more about the whole range of services offered by Sheffield Assay Office, such as our hallmarking and analytical services, please email us at info@assayoffice.co.uk or complete the contact form on our website at http://www.assayoffice.co.uk/contact-us,
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