Diamond Certification

Rebecca Share, gemmologist and trainee valuer, outlines the tasks that she carries out during a typical day in the laboratory.

While AnchorCert deals purely in quality and authentication, not in allocating values, its independent assessment of the stone can have a significant impact on selling price. As recent news headlines from Antwerp have demonstrated, the integrity of the gemmologists and the organisation is paramount. The gemmologist must also be conscientious, vigilant and well versed in the latest treatments, which could easily catch out the less well informed. Enhancement and treatment of gemstones is an accepted practice within the jewellery industry, but they must be disclosed to ensure the stone trades at an appropriate price and is sold correctly.

In a typical day at AnchorCert, Rebecca might start off with a parcel of 10 loose white diamonds from a local gemstone dealer. After these have been booked in, weighed and photographed, it is Rebecca’s task to start the important screening process to ensure that the diamonds are natural and untreated. For this procedure the DiamondSure equipment, specifically developed for the purpose by the Diamond Trading Company, is used. Rebecca says: “The DiamondSure is a ‘must have’ instrument for any serious diamond laboratory. This amazing piece of kit searches for the key absorption line in the main type of diamonds – Type Ia – and gives us an immediate indication as to whether the stone is susceptible to a particular type of treatment – HPHT (high pressure high temperature) – or could possibly be a synthetic. The treatment aspect is very important as it is not something that can be picked up by magnification, and since the diamond’s colour can be improved so vastly, the value could be massively different if the buyer is unaware that it has been treated. This quick screening cannot be achieved by using any other equipment.”

In this case all stones receive a ready ‘pass’ and Rebecca can begin the process of closely assessing the diamonds in order to grade each one for colour and clarity. All is going well until Rebecca spots an unusual looking feather shaped inclusion, too glassy to be normal, with strange black squiggles inside one of the diamonds. Moving from her 10x loupe to a microscope, Rebecca confirms that the inclusion is in fact not natural but the result of a KM laser treatment, which has been used to remove a much larger natural inclusion, thereby improving the apparent clarity of the stone by at least two grades. This is an accepted practice but must be disclosed and so it is clearly included on the AnchorCert certificate when it is printed.

“The customer who submitted this has probably spotted the evidence of KM lasering himself, and sent it to us for an independent opinion,” says Rebecca. “This treatment is increasingly prevalent, even in relatively small stones, and is well documented in the gemmological journals. Although not as easy to spot as laser drilling or fracture filling, the unnatural look of the feather and strange black lines can be a giveaway. It is, however, important not to confuse them with the natural counterparts that they mimic.”

After handing that parcel to a colleague for the second grading to be carried out, to validate Rebecca’s results, the next parcel contains 20 diamond rings, each of the same style. The retailer has bought these to a specification and wants AnchorCert to verify the total minimum weight – which can only be an estimate based on measuring the mounted diamonds and applying a formula – and to check that the stones are natural diamonds, untreated and a minimum J colour, SI clarity

After passing all of the rings using the DiamondSure once more, Rebecca checks the weights are satisfactory easily enough and uses her GIA colour master stones to qualify the colours. However, when it comes to clarity there is a problem. As Rebecca explains, “the tell tale holes on the surface of the table and pavilion indicate that, despite these diamonds weighing only approximately 0.05 carat, they have been laser drilled to remove the dark inclusions and enhance the clarity.” A phone call is required to alert the client that the product has failed as the stones have clearly been treated.

Finally, Rebecca begins work on a loose yellow diamond weighing 1.75 carats; an investigation that any gemmological detective would relish. “A jeweller in a retail store without access to the specialist technology would have no chance of ensuring that this is a natural coloured diamond,” says Rebecca. “Whether it is natural or not could make thousands of pounds’ difference to its value, which is why people send stones like this to AnchorCert.

“Assessing whether the colour of a yellow diamond is natural is a lengthy process and can take hours of analysis over several days,” she continues. “We start off by using the DiamondSure to check for a Type I diamond, which would be the most common for a natural yellow. Although this result is crucial, the diamond must still go for further testing. After a quick look on the DTC DiamondView to confirm that the growth structure of the diamond is natural and not synthetic, we move on to the FTIR – Fourier transform infrared spectroscope – which confirms the ‘type’ we are working with. This helps us to narrow down what sort of treatment we could theoretically be looking for. We then move on to the Raman Spectroscope. The Raman is an unmistakeably fantastic piece of equipment that few people are lucky enough to ever get to use. For us, however, it means we can test for anything as complicated as HPHT treatment on diamonds or as straight forward as gem identification. We are fortunate to have the use of two lasers – the 514.2nm (green) and 633.4nm (red). These allow us to examine a wider area of the visible and near infrared spectrum. After looking for certain peaks, which confirm that this diamond is not treated, we can use the UV-Vis to analyse the ultraviolet range of the electromagnetic spectrum. This helps us to explore which ‘group’ this naturally coloured diamond falls into and to assign a final colour grading.

“Without this equipment and the experience and training we have all had, we could never be sure, but having tested the stone in so many different ways we are confident that we can certificate it as a natural yellow diamond, and our independent, expert report will significantly increase its value.”