Chemical Vapour Deposition (CVD) Diamonds
Modern lab created diamonds are primarily produced by Chemical Vapor Deposition (CVD) when a very hot gas containing carbon is deposited into a chamber at high temperature and pressure. The carbon atoms are deposited onto a diamond ‘substrate’ which can be a naturally ocurring diamond, or one created by the HPHT method. The substrates or seed crystals grow new diamonds at up to half a millimetre per day. The equipment and method for making CVD diamonds is relatively simple compared to the HPHT process.
CVD diamonds can be produced with good clarity although they can also have brownish tints or faults. The clarity can be improved by using a HPHT process after the CVD diamond has been produced.
CVD diamonds can be difficult to distinguish from natural diamonds with the naked eye, or even standard gemmological instruments. Various lab tests can be used to identify them easily though, including Cathode Luminescense which identifies the growth pattern of the crystal. Some CVD diamonds may fluoresce under UV light, a feature rarely seen in natural diamonds.
There is a great article here about how CVD diamonds are made – I definitely recommend reading this if you are interested in the topic. This article is one of the things that got me really interested in how diamonds are made, and how they can be such a good alternative to the real thing!