Over the past decade, significant technological advances have meant that diamonds can be grown above-ground in a lab environment. These diamonds are physically, chemically and optically identical to a natural mined diamond - without the conflict issues and environmental displacement typically associated with the diamond industry.
Lab-grown diamonds are grown using a ‘seed’, taken from an existing diamond. This seed is then placed in a chamber that replicates the heat and pressure conditions occurring naturally underground, creating a diamond in a matter of weeks; rather than over several thousand years. These lab-created diamonds come out as rough crystal, and get cut, polished and graded in the same manner as a mined diamond.
There are a variety of techniques used to make a diamond in a lab - but the result is a diamond with the same properties and sparkle of the highest grade of naturally-occurring diamond.
Chemical Vapour Deposition (CVD)
The CVD method is used to grow top level gem-grade diamonds, as well as for other uses like optics. This technique uses extremely pure, carbon-rich gasses (like methane) in a controlled chamber. This gas is then heated until it separates or breaks down, isolating the carbon atoms.
These carbon atoms then fall down onto a diamond substrate, building up the layers of rough crystal to be cut.
The whole process takes between 6-10 weeks, and produces a high-grade Type IIa gemstone.
Type IIa Diamonds
Type IIa is the purest type of diamond there is, meaning there are little to no nitrogen atoms present in the crystal structure. They are highly sought after for both their rarity and their exceptional optical transparency, giving them a dazzling effect. Type IIa make up only 1-2% of all mined diamonds, which means they sell at a high premium.
High Pressure High Temperature (HPHT)
The HPHT method uses chambers to recreate the temperatures and pressures of deep underground, where diamonds are naturally formed by nature. These machines can produce a pressure of almost 60 000 atmospheres and temperatures of up to 2500℃.
HPHT labs place a cell into this chamber containing a seed, along with refined graphite and a catalyst mixture of metals and powders.
In the chamber, the catalysts react first, changing from solid to a molten state as the temperature approaches 1300℃. This molten solution dissolves the graphite into carbon atoms. The cooling process then takes place over several days, allowing these atoms to build up on the seed into the crystal formation.
The HPHT technique requires an extremely controlled environment to produce high-grade gems. Just like in naturally occurring diamonds, any changes to temperature or pressure will affect the growth and quality of the diamonds. The entire growth cycle needs to be fully completed before the colour and clarity of the diamond can be determined.
The 4 C’s of diamonds
Diamonds are graded using the 4 C’s; Cut, Colour, Clarity and Carat weight. Knowing the 4 C’s will help with your knowledge of a high quality diamond vs a low quality one.
The cut of a diamond refers to the precision and methods used to cut and polish a diamond for maximum light performance. There are 5 grades of cut: Ideal; Excellent; Very Good; Fair; and Poor.
The quality of the cut of a diamond is judged by:
- Brightness: how much light is reflected - well-cut diamonds will reflect nearly all light back out, making them bright even in poor lighting.
- Fire: the rainbow spectrum of colours reflected.
- Scintillation: or ‘sparkle’
- Pattern: the contrast in light and dark areas within a gemstone. The better the cut, the better the contrast and structural uniformity.
A perfect diamond is completely colourless. Colourless diamonds are limited to less than 2% of all diamonds; more than 98% of diamonds have nitrogen impurities, tinting them yellow or brown.
A very small percentage (less than 1%) of mined diamonds are in ‘fancy’ colours such as red, blue, or pink. These occur due to small amounts of specific trace elements present during the growth phase.
Diamond labs have standardised coloured gems with letter grades D-Z, for example:
- D,E, and F are colourless gems; and G, H, I and J are near colourless.
The fancy coloured diamonds can be replicated in the labs by introducing the specific trace elements required.
Clarity is a measurement of a diamonds blemishes or imperfections. The purest form of diamond is classified as Type IIa, with almost none or no impurities at all. However, all diamonds are on a spectrum of 5 grades:
- Flawless/Internally Flawless (FL, IF)
- Very, Very Slightly Included (VVS1, VVS2)
- Very Slightly Included (VS1, VS2)
- Slightly Included (SI1, SI2)
- Imperfect (I1, I2, I3)
This covers everything from a Type IIa diamond, down to the lower grades where the imperfections are easy to see with the naked eye. These diamonds are more likely to crack or break, and makes up the majority of mined diamonds.
When a diamond is properly cut, the carat weight also defines the size of the gemstone. As a reference: 1 carat = 0.20g. Smaller diamonds are measured in ‘points’: 1 point = 0.01 carats. The carat system works the same as money; where $1 = 100c, 1 carat = 100 points.