Science and testing of Synthetic Gemstones
Most natural diamonds are formed under high pressure and extreme heat, deep in the Earth, and take billions of years to form. Diamond-bearing rocks travel towards the surface when magma moves upwards in ’pipes’ (volcanic eruptions that don’t quite reach the surface). People then mine the diamonds either directly from the pipes, or from the alluvial deposits where diamonds that have been eroded from the rock naturally accumulate. This formation and transportation process leaves telltale markers on the diamonds which are very hard to simulate, and as such, even the best synthetic diamond can be told apart from their naturally occurring relatives. Often the only way of telling them apart means sending them off to a lab like the GIA to get them assessed using much more advanced scientific tools.
One method of assessment is to identify what type the diamond is. The vast majority of natural diamonds are type Ia. Type Ia diamonds contain lots of nitrogen in clusters or pairs. This kind of diamond cannot be grown artificially. Type Ib diamonds contain scattered and isolated nitrogen atoms that are not in pairs or clusters. Synthetic diamonds correspond to types Ib, IIa, and IIb, and are all rare among natural diamonds.
How are Synthetic gemstones made?
One of the ways of ‘growing’ diamonds synthetically, is called HPHT (High Pressure, High Temperature). This subjects a starter ‘seed’ to high pressures and temperatures in a similar way to what would have happened in the ground. This happens over a number of weeks or months rather than billions of years, though, and as such the crystal structure and growth patterns within a synthetic stone are very different to those in a natural one. Most HPHT-grown crystals are yellow, orangey yellow, or brownish yellow. Colourless HPHT synthetics have been difficult to create as it requires longer growing times and more stable, nitrogen-free growing conditions.
Another way of growing diamonds is called CVD – Chemical Vapour Deposition. This process effectively microwaves a gas that contains carbon (like methane) and the resulting carbon atoms are attracted downwards to create flat plates of diamond. As with HPHT, the process takes place over a number of weeks, but these crystals tend to be brownish or greyish. If there is a tiny amount of nitrogen or boron into the crystalisation chamber, yellow, pink-orange, or blue crystals are likely to occur instead. Colourless crystals can be grown, but they either take longer to grow, or the CVD has to be combined with HPHT to remove the colour.
HPHT and CVD both produce clear, synthetic diamonds, which to the naked eye are impossible to tell apart. We have used synthetic diamonds when customers have specifically asked for them, most notably customers who are really interested in the science behind making a diamond. The ethics surrounding synthetic diamonds is subjective; whilst one person might favour the artificial process, another may prefer to support the livelihood of the diamond miner.