Much of the diamond jewellery that I see is mounted, which makes grading them challenging. In July, I enrolled in a week-long course offered by the National Association of Jewellers and taught by the renowned Eric Emms. Understanding that mounts can affect a diamond’s colour and that claws can easily hide a flaw can seriously affect the value if graded incorrectly.

Despite my years at Sotheby’s looking at mounted and unmounted diamonds, it’s always good to go back to the basics. With just a loupe and a microscope to reconfirm my findings, the days were filled with looking at simulants, fracture-filled and actual diamonds.

Several times I surprised myself by discovering inconspicuous drill holes. Often included diamonds are laser drilled to better their colour. I think I can confidently identify a fracture-filled diamond by its “purple flash”, another method used to make diamonds whiter.

There are so many stimulants and treated diamonds on the market today. Often it’s disclosed, but when it’s not, it’s up the jewellers and valuers to identify them. The only way for this is practice, practice, practice!

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