Identify diamond treatments

Technologies for diamond treatments

The treatment used to improve the appearance of natural diamonds include laser drilling, typically followed by acid treatment, to remove the black inclusions; the filling of large surface-reaching fractures with high-refractive-index glass; and color enhancement by various procedures. Two of the most important developments in the decade are:

* A new type of laser drilling, KM treatment (Kiduah Meyuhad means”special drill” in Hebrew) for removing inclusions (Horikawa 2001). This procedure produces an internal, surface-reaching fracture that looks more like a ‘feather’ than a traditional laser-induced channel, but still allows introduction of an acid to dissolve the inclusion.

*High-pressure, high-temperature (HPHT) processing which causes dramatic changes in color. The HPHT process combined with the older techniques of radiation and heat treatment to produce fancy pink-to-red specimens. Diamonds enhanced in this way by Lucent diamonds Inc. Of equal, if not greater, importance is the ability of HPHT processing to produce colorless or near colorless stones from brown type IIa diamonds. This treatment also occasionally results in pink or (more rarely) blue specimens, which have absorption spectra that are similar to those of naturally colored diamonds.

Although most color enhancement of diamonds is done legitimately, and the process declared, some treated diamonds may be fraudulently described as having a natural color as they travel through different distribution channels. Therefore, it is vital that gem-testing laboratories have the experience to recognize color-enhanced diamonds and that research into their characterization and identification continues to keep up with the new enhancement techniques as they are introduced. All colored diamonds need to be examined carefully; furthermore, in principle, any colorless or near-colorless diamond is potentially a type IIa diamond that has been color-enhanced(from brown) by HPHT processing. Fortunately, it is quick and easy to determine whether a diamond is type IIa (by using Diamondsure or a similar instrumental), and the majority of diamonds (around 99%) are not in fact, type IIa.

Visual inspection with a 10x loupe an optical microscope (to detect drill holes and feathers produced by lasers, as well as the “flash effect” associated with glass-filled fractures together with optical absorption and luminescence spectroscopies, enable detection of most treated diamonds (some more readily than others). Visual evidence of graining, as well as graphitized cracks and inclusions also give important clues that the diamond has been subjected to HPHT processing. However, despite the range of assessment techniques available, it is likely that a few diamonds will be encountered for which it is not possible to say with certainty whether the color is natural or enhanced. Recent research indicates that the phosphorescent behavior of blue diamonds produced by HPHT processing is different from that of a natural blue diamonds, and this observation may provide an additional analytical tool for examining certain stones. The KM laser treatment can often be verified by examining polishing marks on the diamond’s surface by differential interference microscopy.


Fancy Deep Pinkish Purple Diamond

Fancy deep pinkish purple, natural color

Understanding the HPHT processing

If a diamond is heated to above 750 degree Celsius in the air, it will start to burn. However, if the diamond is under extreme pressure, similar to natural diamond formation, then even temperature up to 2000 degree Celsius will not cause significant degradation. These extreme annealing temperatures create the conditions for the diamond to change color. While the concept is easily understood, many do not fully appreciate the investment and the maintenance demanded by this technology. Sundance Diamonds uses a propriety press that was developed for HPHT processing that costs close to $1 million. Providing the extreme conditions necessary for this process creates the need for continual maintenance with costly materials. Sundance Diamonds could not survive without its parent company and their team of scientists and engineers to support and maintain the equipment. Even with continual investment to reduce the risks and optimize the outcome, HPHT treatment remains a volatile process with the possibility of fracture and complete loss of the diamond being treated.


Fancy Vivid Blue Green Diamond

Fancy vivid blue-green, natural color


Traditionally, the HPHT process has been used to reduce brown hues in type IIa diamonds to appear colorless or near colorless. Now through years of research, almost all brown diamonds can benefit from HPHT technology. Nitrogen, a common diamond impurity, can be manipulated at high temperatures to yield colors that are rare in nature. Green and intense yellow were the first colors to show promise, with irradiation, pink and purple are now possible. With ongoing research, we hope to be able to present a whole rainbow of reproducible colors. All of these niche colors offer the potential for additional usability and profit from brown diamonds.

Light Champagne Diamond

Light brown, natural color