The first thing you should know is that there are two methods for growing synthetic stones. The first is High Pressure-High Temperature(HPHT), the second is Chemical Vapor Deposition (CVD). According to Thomas M. Moses, Senior VP of GIA's Laboratory and Research Department, the processes used are both costly and challenging but produce gem quality stones. However the diamonds produced vary greatly in characteristics.
HPHT:Moses explains that HPHT was originally introduced by General Electric (GE) in 1954 and mimics the intense heat and pressure that crystallizes carbon into natural diamonds. These kinds of stones are made in a press that is capable of generating these extreme conditions. Today there are a variety of these apparatus all with a growth chamber where HPHT diamonds are grown from carbon molecules in a metallic solvent catalyst that is usually made of iron or nickle or a mixture of the two.
The growth time for these stones is on average one week, not too long but the growth chamber is very small, so only a few may be grown at a time. Because of this draw back most HPHT stones are .50 carats. Moses says that while this method has been around for over half a century now, it is only recently establishing profitability.
THE CHARACTERISTIC OF HPHT:
Diamonds are scientifically classified by type based on the amount and location of the impurities they contain. Almost all HPHT stones are type Ib, with up to 0.5% nitrogen dispersed throughout the stone. Because the nitrogen is dispersed, almost all of these stones have an identifiable color. The majority of HPHT stones are in the color grades H-P, the trace of nitrogen atoms is responsible for the yellowish brownish tint. Under the Microscope, HPHT stones are inherently shaped differently than natural ones. The HPHT method typically grows cube-octahedral like crystals. Also, because they are grown in metallic solvents, some stones have metal inclusions.CVD:
The CVD method differs greatly from HPHT in that "synthetic diamonds are produced by using microwaves or other sources of energy to break down hydrocarbon gas, such as methane, inside a vacuum chamber. This causes carbon atoms to accumulate in thin layers on a flat diamond substrate-similar to the way snowflakes accumulate in a snowfall," explains Moses.
This process is a slow one, only .10 mm of diamond can be grown per hour. This method for growth also has it's limits in depth. CVD stones over 3mm in depth are extremely difficult to grow.
The CVD method was first successfully tried by Huston, Texas-based chemical manufacturer Union Carbide Cooperation in the 1950's. It is less costly and challenging than HPHT, but like the HPHT method it has only recently become economically viable.
THE CHARACTERISTICS OFCVD:
Due to their unique growth process, CVD stones are type IIa, which contains negligible amounts of nitrogen and high thermal conductivity. This method produces flat tubular synthetic diamond crystals. Because of the gasses used these stones are also brownish in tint.SYNTHETIC TREATMENT:
Because of the synthetics and their inherent color, manufacturers have begun treating the stones, post-growth, to transform the unattractive brownish yellowish tints into vivid colors. Through these processes most natural stones can also be altered to a desired color.
Companies like Suncrest Diamonds, based in Orem, Utah use HPHT processing for just this purpose. Due to ongoing advances in the HPHT process, stones can not only be transformed into an array of colors, but also improved as white diamonds.Not to worry here, the differences in Natural stones and Synthetic ones are well known and documented. For a gem lab they are easy differentiators, to the naked eye of man, not so much. I for one have no doubt that technology will continue to increase and the demand for "better than natural" looking synthetics will increase with it.
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