The Gold Eureka October 09 2016
Eureka! Eureka! The story of Archimedes jumping out of his bath tub in revelation of a profound solution has been with us for centuries. The legend highlights the Greek scientist’s response to the gold testing problem: to determine, without damaging, whether the new crown of King Heroin II of Syracuse is of fine gold or a suspected adulterated alloy. His solution, of course, was the principle of density which we vaguely remember from one of our earlier physics classes. In essence, the amount of water displaced from a tub of water when the crown is immersed in it should be equal to that displaced by a similar object of known gold purity. The tests for gold purity has advanced by leaps and bounds since this early ‘hydrostatic density’ measurement but this story puts forward an important requirement of the gold industry – a test that is rapid, simple, consistent, relatively inexpensive & non-destructive.
One of the earliest institutions responsible for ascertaining the purity of gold and hence protecting consumers is the Worshipful Company of Goldsmiths in London. From the Kings of early 1300s to the bustling economy of today, the United Kingdom among many other nations, require all items of gold sold to be sent to assigned assay offices for ‘hallmarking’ – an authentication process by which the gold may be certified through four or five marks indicating the sponsors mark, the finesse in parts per thousands and the year of marking. Although some nations may show slight differences, the standard policy is to have a zero negative tolerance for a stated purity. For example, a 749 part per thousand gold cannot be marked as 18 karat gold which is standardized at 750 parts per thousand. At present, international standards put forward by the “International Convention on the Control of Marking Articles of Precious Metals” guide the standard karat weight and enable countries to accept gold from other nations which have been tested by authorized laboratories without further verification.
Gold Assay reports employ a variety of techniques to determine the purity of gold. In addition to the hydrostatic density technique, fire assay is another one of the earliest form of gold testing. It involved oxidizing the metal at a high temperature in an attempt to separate the base and noble metals. Residual metals are dissolved away using nitric acid and the weight of the remaining fine gold is compared to the weight of the original sample. These methods, rudimentary at best, served well during the early ages of the jewelry industry but with enhanced technology, stricter demands for quality and an increased competitive landscape they were quickly replaced by tests offering higher reliability and accuracy.
One of these newer techniques includes a form of spectroscopy called directly coupled plasma (DCP). An improvement upon its predecessor, atomic absorption, DCP places a sample of the gold in a liquid solution and excites it using a high temperature plasma. The excitation releases light at certain wavelengths which can be measured based on the signature characteristics of elements present in the sample. This method vastly improves the achieved accuracy to an order of 1 part per million but is compromised in its ability to process large batches in an automated fashion. Hence, the cost of using this advanced method has become a large hindrance for its implementation in laboratories across the world. Another advanced test involves x-ray fluorescence which came in to play in the 1960s with the rapid development of computer technology. In this method, a sample of the tested material is struck with an x-ray and the resulting secondary x-ray emitted is collected and scrutinized for the composition and proportion of elements present. Once calibrated to comparable standards and synchronized using powerful data aggregators, this method produces results with much greater accuracy that DCP spectroscopy. Once again though, issues related to the short wavelength of x-rays and the need for internal homogeneity of the metal, surface sensitivity affecting valid data collection and the costs related to purchasing and training personnel to use this machinery makes it an incredible challenge to implement industry-wide.
With advances in technology come better expertise and falling costs and these are significant factors that contribute to improving the metallurgical assay tests used by the jewelry industry. As is with most of life, the key here is to strike a balance so that the tests are not only reliable and accurate but also cost effective to utilize in large volumes of samples. A eureka moment may not be available to enhance the testing methods overnight but improvements are made gradually and surely to foster an environment of increased trust between retailer and client.
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