As lab-grown diamonds grow in popularity, jewellers want to know if modern processes that change the colour of the diamond are permanent.
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Efforts to enhance the colour of natural diamonds began centuries ago with oils, dyes and bright foils applied to the pavilions of diamonds in closed-back settings. In modern times, more sophisticated chemical coatings can be used to lighten the apparent colour of diamonds in the D-Z range. These treatments can be scratched, worn off or altered by heat or chemical exposure and are therefore not considered permanent. Therefore, IGI will not issue a grading report for such diamonds.
What about lab-grown diamonds?
As lab-grown diamonds continue to grow in popularity, we are asked whether the modern processes commonly used by growers to reduce, eliminate or alter the colour appearance of a lab-grown diamond are permanent. The short answer is yes.
Fun Fact – Most diamonds in the world are brown.
Brown is the most common colour variety of gem-quality diamonds, whether natural or lab-grown. Brown diamonds account for approximately 15% of the production of most natural diamond mines. Brown is also present in the majority of lab-grown diamonds, although this number is decreasing as technology advances. This colour is slightly more common in rough crystals grown using the chemical vapour deposition (CVD) process than the high pressure high temperature (HPHT) process.
What causes brown colour?
Brown colour in diamonds is due to the way atoms arrange themselves during growth, resulting vacancy clusters, etc. Common methods of reducing, eliminating or altering brown colour in lab-grown diamonds are exposure to post-growth HPHT for stones grown by either method; or exposure to post-growth Low-Pressure High-Temperature (LPHT) for CVD-grown stones. These intense processes help to rearrange the atoms so that the brown colour is reduced, eliminated or changed to a softer shade such as grey or pink.
Stability
Today’s HPHT and LPHT treatments, along with modern irradiation, annealing and multi-process treatments (used to enhance fancy coloured lab-grown diamonds), change the structure of the gemstone at the molecular level. This makes them perfectly stable for regular wear. To change the atoms of the material again would require exposure to an equal or stronger process, so the modern treatments used to enhance the colour of lab-grown diamonds are considered permanent.
Further reporting
Where available, IGI will report relevant colour information beyond the D-Z grade of the diamond. Most jewellery professionals are aware that diamonds can have a yellow, brown or grey body tone. Diamonds can also have a blue, pink or green body tone. These hues are less common in natural diamonds than in lab-grown diamonds, so knowledge of them is not as widespread.
IGI colour notations outside the colourless range.
If present in the GHIJ range: IGI comments include Faint Blue, Faint Pink or Faint Green.
Blue, pink or green at saturations above J are considered Fancy Light.
Blue, pink or green in saturations N-Z are considered Fancy
If present in the KLM range: IGI comments include Faint Brown or Faint Grey
If present in the NOPQR range: IGI comments include Very Light Brown or Very Light Grey
If present in the S-Z range: IGI comments include Light Brown or Light Grey
Note that colour grades below N are reported as a two-letter range (N-O, O-P, etc.).
Optional
For yellow diamonds in the N-R range, IGI may include the comment Very Light Yellow.
For yellow diamonds in the S-Z range, the IGI may include the comment Light Yellow
