Cultured or synthetic diamonds are real diamonds that have been created in the lab instead of by geological processes. These man-made diamonds, are almost always ‘fancy coloured’ – most often yellow – but far less expensive than natural fancy coloured stones, and represent a great option for those seeking diamonds that are guaranteed to be conflict-free.
After the discovery in 1797 that diamonds were made from pure carbon, a number of scientists started trying to create them – a few with some limited success, though no reliable method was developed until the 1950s. Synthetic diamonds are now made in two main ways, HPHT (high pressure, high temperature) and CVD (chemical vapour deposition).
HPHT stones are made by subjecting carbon to extreme heat and pressure by means of a mechanical press and electrical current; CVD diamonds are ‘grown’ at much lower pressures by building up layers on a base surface from surrounding plasma. The control and flexibility inherent in this process lends it to industrial applications, such as coating machine components. However, both HPHT and CVD stones can be and are used as gemstones.
They may be coloured, like natural stones, depending on the impurities present in the manufacturing process, and can be machined like mined diamonds. This has led to the creation of a new suite of technology aimed at distinguishing natural from synthetic stones.
Man-made diamonds may have better or worse properties than their natural counterparts, depending on various factors in their manufacture. They may, for example, be harder, or have better conductivity (of heat or electricity). As important is the method of manufacture: CVD is particularly useful for certain applications as it makes it possible to coat large surfaces with a thin film of diamond. Synthetic diamonds are often used in abrasives and cutting tools.
Due to the nature of the technological processes involved, synthetic diamonds are usually fairly small. Theoretically, large diamonds could be grown and probably will be one day. For now, however, this is prohibitively expensive and the largest diamonds are still natural. De Beers has grown 25 carat stones, but most are no more than 1.5 carats. By contrast, the largest natural rough diamond was in excess of 3,000 carats, and the largest polished stone was more than 500 carats.