Many consumers believe it’s impossible to distinguish between a natural diamond, formed in the Earth, and a man-made or laboratory-grown diamond. However, this is not true and there are ways to verify that a diamond is natural.
LGDs are produced in environments that differ significantly to natural diamond formation and are produced by two primary methods: high-pressure, high-temperature (HPHT) and chemical vapour deposition (CVD). Each of these production methods produce LGDs with forms that differ from natural diamonds.
HPHT LGDs exhibit a cubo-octahedral morphology, appearing more blocky than natural rough crystals. This shape results from the cube and octahedral faces growing at similar rates during the shorter growth period, typically a few weeks, preserving the cube faces. In some cases, the yellow synthetic grit “seed” crystal remains visible in the rough form.
Natural diamonds, on the other hand, grow over much longer periods, with the octahedral faces developing more slowly, resulting in the distinctive octahedral shape associated with natural stones.
CVD LGDs are grown on a large, polished plate that serves as a substrate; this leads to their blocky tabular shape. They can consist of black polycrystalline material around the edge, but this will be removed when manufacturing the stone.
Once a diamond is polished, the external morphology information is no longer visible, but the intrinsic properties and unique characteristics remain. It is the trace elements and the distribution of these elements, within the crystal structure, that allow exploratory techniques to aid in identification. One of these techniques is fluorescence imaging.
The DiamondView™ instrument uses short-wave ultra-violet (SWUV) light to excite fluorescence in diamonds. By examining the colour of the fluorescence and any growth features or markings, it is possible to determine whether the stone is natural, or laboratory grown.
Trace elements within the diamond and the arrangement of these can cause distinct fluorescence colours. Growth patterns, such as growth banding and dislocations, are characteristic of natural diamonds, whilst lab-grown diamonds show different features, blocky growth sectors in HPHT and striations in CVD laboratory-grown diamonds.
The DiamondView™ is a valuable tool not only observing the fluorescence but also detecting the phosphorescence or ‘after-glow’ of a diamond. Once the SWUV source is switched off, the instrument checks for any long-lived phosphorescence, which is a phenomenon seen in colourless HPHT LGDs. Together with the fluorescence colour and distinctive growth features, this helps accurately identify these LGDs.
