What is Hallmarking and Why is it Important?By Ng Siew Hua, Chief Assayer, Singapore Assay Office
Published on September 25, 2017
Hallmarks are a form of consumer protection and guarantee of the purity of precious metals. They include symbols identifying the assay office, purity of metal, and often marks representing the date and manufacturer. Assay offices randomly test batches of goods from manufacturers and if these samples are as described, mark them with a special hallmark.
SAO’s role is to ensure a consistent and systematic hallmarking practice in Singapore. With over 40 years of experience, SAO is an established accredited assaying and hallmarking office, reinforcing consumer protection among shoppers, gold retailers, suppliers and traders. SAO’s hallmarking is a voluntary scheme where manufacturers, traders, and retailers of gold jewellery submit their jewellery pieces for assaying and hallmarking. The scheme facilitates two procedures: testing and hallmarking.
To ascertain the homogeneity of a batch of articles, sampled samples will undergo fire assaying, and SAO will screen the batch of jewellery using the X-ray fluorescence (XRF) material analysis method (Image 1). XRF is a non-destructive material analytical method to determine the homogeneity of a batch of articles. In this process, a sample is irradiated with X-rays from a controlled X-ray tube. The X-ray emission penetrates only the surface of the sample to determine the elemental composition of the metal.
Samples from the batch are then analysed by fire assaying, a destructive method. The sample is weighed, and placed in a high-temperature furnace for oxidation to remove base metals, a process known as cupellation. The molten globe consisting of gold/silver is then treated with nitric acid after cooling to separate silver from gold. The gold sample is then weighed to determine its purity.
Items that meet purity standards will undergo the hallmarking procedures. Items that do not meet standards would then be investigated to determine if it is sub-standard. Fire assaying is an internationally accepted test method to determine the precious metal content present.
If the samples in a batch being tested meet industry standards, SAO will hallmark every piece of the jewellery in the batch with a SAO mark that bears the symbol of a lion’s head to attest to its quality. The complete set of hallmarks consists of the SAO mark, the standard mark and the jeweller’s mark (Image 3).
Handmarking, whereby articles are hand-struck with a metal punch and a hammer (Image 4), is the most traditional form of hallmarking. Today, laser marking is widespread, and is done using fine, high-powered laser beams (Image 5). This method can also be used to mark signatures and logos.
To maintain SAO’s high standards and to align them with international assay offices, SAO regularly attends the conference organised by the International Hallmarking Convention, and actively participates in the annual proficiency test programme organised by the International Association of Assay Offices (IAAO). SAO also works with organisations such as Consumer Association of Singapore (CASE) and Singapore Standard Council (SSC) to protect the interests of consumers of precious metal articles.
For more information, please visit www.assayoffice.com.sg.
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