Screening for synthetic diamonds using standard gem instruments
Part 6 of 6
By Branko Deljanin
Visually, natural and synthetic diamonds can look very similar when comparing size, cut, colour, and clarity. Yet, their commercial values differ significantly, which highlights the importance of detection and disclosure. For instance, coloured synthetics can cost 50 to 60 per cent less than their natural counterparts. In the case of colourless lab-growns, the price difference is around 25 to 30 per cent.
Many dealers and retailers believe diamonds exhibiting medium, strong, or very strong blue fluorescence are inferior. However, visible strong blue fluorescence under long-wave light is a very strong indication of a diamond’s natural origin.
In combination with the simple CPF method, the fluorescence technique can be used to screen for diamond types and help identify synthetic origin of a coloured diamond, as well as colourless without pattern (i.e. HPHT), even with diamonds less than .50 carats.
However, in cases where the diamond is determined Type IIa based on the ‘tatami’ pattern, it is still very important to refer it to an advanced lab to determine whether colour is natural or HPHT-enhanced, or the stone is CVD-grown.
The procedures explained here are relatively simple, easy to learn, and inexpensive. A CPF set and UV lamp costs about $500. In light of several occurrences of salted parcels of undisclosed diamonds reported in the last few years, vigilance and an understanding of gemmological tools are critical to ensuring confidence in the supply line.
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