The initial confusion: what’s in a name? It appears the industry prefers the term ‘lab-grown’ or ‘lab-created’ diamonds to ‘synthetic’ diamonds. Technically, ‘synthetic’ is the most accurate term, although both ‘laboratory-grown’ and ‘laboratory-created’, without shortening to ‘lab’, are also accepted by the CIBJO industry standard.
These names all represent diamonds manufactured in a laboratory that have the same chemical composition and physical properties as natural diamond.
On the other hand there are synthetic stones designed to look like diamonds but they are not the same chemically and/or physically, such as cubic zirconia and moissanite. These are termed 'imitants'.
The first recorded synthetic diamonds were largely experimental, designed for use in advanced technological settings. In 1970, General Electric announced it had produced gem-quality colourless, blue, and yellow synthetic diamonds suitable for the jewellery industry.
As technology and the understanding of diamond synthesis improved, new variations of these gems were produced including synthetic blue diamonds, supposedly ‘grown from human remains’!
The first method of diamond synthesis responsible for commercially available synthetic diamonds, still available today, was a High Pressure High Temperature (HPHT) synthesis. This aims to recreate natural diamond growth by subjecting carbon to extreme pressure and temperature, as the name suggests.
The apparatus grows diamonds at pressures around 53,000 atmospheres (1 atmosphere is the average pressure we feel on Earth) and temperatures around 1,300–1,600°C.
Generating this level of energy is expensive and requires larger equipment than the more recently introduced synthesis method of Chemical Vapour Deposition (CVD). This method is very different to the geological processes that create natural diamonds.
CVD diamonds are grown within a vacuum chamber from a gas containing carbon, such as methane. Exposing the gas to microwaves ionises the carbon atoms, which deposit and grow on a diamond seed crystal within the chamber. Over time, changing the gas used and the purity of the diamond seed plate has resulted in better quality CVD synthetics.
CVD synthetic diamonds are usually Type IIa – a ‘purer’ type of diamond with negligible nitrogen impurities, found in only 2 per cent of natural diamonds.
Although HPHT synthetic diamonds were mostly Type Ib in earlier production, introducing a new step in the growing process means Type IIa are now commonly grown for the jewellery industry.
These days, portable testing equipment designed to identify and separate colourless natural diamonds from synthetic, such as the Presidium Synthetic Diamond Screener II, measure diamond’s response to ultraviolet light in order to suggest whether it may be Type IIa.
In the screening process, any colourless diamonds that show signs of being Type IIa should be sent to a gemmological laboratory for further testing for confirmation of natural or synthetic growth.
The most well-known features of synthetic diamonds include metallic inclusions in HPHTs (which can cause them to be attracted to magnets), stronger fluorescence in short-wave ultraviolet light than long-wave (the opposite of natural diamonds), phosphorescence, and strain patterns caused by the growth process and their different morphology (crystal shape), which varies between HPHT, CVD, and natural diamonds.
Accurate and reliable identification can be simple by identifying growth patterns, fluorescence and phosphorescence, or it may be difficult, requiring more advanced gemmological testing, such as spectroscopic analysis.
As technology continues to improve, disclosure and education become increasingly important. Next month will provide insight into the treatments that may be applied to synthetic diamonds in Synthetic Diamonds: Part II.
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