People have revered diamond as a precious product of nature for thousands of years, especially in India where the tradition of diamond trading and wearing dates back some 3000 years. In the last half century, scientists have discovered ways to alter the appearance of natural diamond: namely to improve clarity and improve or change colour. While treatments can make diffi cult-to-sell diamonds more attractive, they do present identifi cation challenges to the industry if sold undisclosed Detection and disclosure is the key. Diamond treatments are legitimate and can make some diamonds moremarketable, but the need for positive, ethical disclosure is essential to protect the trade and consumers.

Treatments For Colour

Scientists have experimented with many ways to change and modify diamond colour.

Irradiation

Sir William Crookes was the fi rst to changediamond colour by irradiation. He buried diamonds with radium salts for one year in 1904, which turned them green. Unfortunately, it also made them highly radioactive. Development of nuclear reactors, particle accelerating machines, made treatment of stones easier. This caused damaged to the crystal lattice of diamond, altering light absorption, therefore the visible colour. This treatment resulted in only shallow penetration of atomic particles into the diamond, causing distinct colour zones. Researchers developed the linear accelerator in the 1900s. This also accelerates atomic particles, but along a straight path rather than a circular one. Today, penetration with high-energy electrons in a linear accelerator is one of two frequently used irradiation techniques. Depending on the material and treatment conditions, this process usually produces blue or blue-green colours. The other technique involves bombardment with neutrons, usually in a nuclear reactor. Diamonds treated this way usually become green, blue-green, or dark green. Both of these modern processes produce uniform colour without zoning because the electrons and neutrons penetrate very deeply. Colour-modifying irradiation treatment always comes after a diamond is cut and polished. Irradiated colours are sensitive to heat. Technicians use cold running water to prevent colour changes during the irradiation process, which generates a lot of heat. After the gem is set, the heat from jewelry repairs, recutting, or repolishing might also change its colour. A controlled heating and cooling process called annealing, is another way to change diamond colour. When it follows irradiation in a two-step process, annealing modifi es irradiated colours to produce brown, orange, or yellow. Rarely, it can also produce shades of pink, red, or purple. In the 1970s, many diamond colours were modifi ed this way.

Detection

There are some clues to colour treatments that you can detect under magnifi cation, with fairly simple equipment. Colour zoning parallel to facet junctions is one sign of a cyclotron-irradiated diamond. If a brilliant cut is irradiated from the pavilion, the colour zone is an umbrella-shaped area around the culet. If it was treated from the crown, the zone is a dark-coloured ring just inside the girdle. If you see either type of colour zoning, you should send thediamond to a gemological laboratory for further testing.

Coatings

One of the earliest methods of treatment was to use an indelible ink, or a dye called gentian violet, on the culet or the pavilion of the stone. The girdle was marked by the moistened pencil or the pavilion was dipped in the coloured solution. The girdle’s matt surface made it easier to mark or apply various dyes. This would change the apparent colour of the diamond to that of the dye colour. Such coatings can usually be seen with a 10x lens because they tend to be streaky. They may be removed by water, alcohol or a commercial jewellery cleaner. Attempts to improve this treatment by using techniques used in camera lens and spectacles were made after World War II. This changed in recent years with the introduction of a new coating method developed and marketed by Serenity Technologies. These modern silica coatings are applied to polished colourless or near-colourless diamonds and results in a variety of natural-looking fancy colours, including pinks, oranges, yellows, blues, and violets. These coatings are fairly durable, but not permanent. They can be damaged by the heat and chemicals used during jewelry repairs and polishing and can also scratch fairly easily. This means detection and disclosure are vital when handling coated colour-treated diamonds.

Detection

Identifi cation of colour coatings is often easy with simple 10X magnifi cation. Some visible features were scratches and other surface features, such as areas with uncoated spots or patches.

  

High Pressure High Temperature

Advances in diamond synthesis in the late 1990s led scientists to experiment with ways to modify colour of natural diamonds using combinations of high temperature and high pressure. The colour-altering procedures have been publicized in the diamond trade as high pressure, high temperature processes, often abbreviated HPHT. Those experiments resulted in two different processes. One improves the colour of a relative few brownish diamonds, making them almost colourless. The other creates green or yellowish green diamonds from brown stones. The improvement in colour can be dramatic. Brown diamonds of N to O colour, and even Fancy Light brown diamonds, can attain D to H grades after HPHT. Today, more colours can be produced: light blues and light pinks that often resemble natural diamonds.

Detection

Identifying HPHT diamonds involves specialized laboratory techniques such as spectroscopy and photoluminescence, but it might be possible to detect some signs with microscope examination. Those signs include damage caused by the extreme heat and pressure conditions, like etched or frosted naturals and fractures that appear frosted or that converted to graphite, often in areas in fractures and around feathers.

Conclusion

Most colour treatments are diffi cult to detect outside of a laboratory. It’s best to send diamonds you suspect of being treated to a well-equipped gemmological laboratory, like the GIA Laboratory, because sophisticated laboratory equipment provides the most reliable origin of colour identifi cations. A spectrophotometer, for example, is a complex and expensive instruments that reads a gem’s light absorption across the visible, UV, and infra red ranges. Experienced technicians can detect that information and usually make an origin-of-colour judgment.

Gem and Jewellery Resources in India

GIA grading reports and professional training are essential tools for enhancing consumer trust in the retail associate’s expertise. As India’s market for diamonds and gems continues to dramatically grow, so too have the resources available to jewellery professionals. They include:

GIA Laboratory– GIA tests every diamond it grades for laser drilling, fracture fi lling, irradiation, high pressure/ high temperature (HPHT) and chemical vapor deposition (CVD) to detect known treatments and separate natural diamonds from synthetics. GIA’s laboratory in India, located in Mumbai’s BandraKurla Complex, grades D-Z color diamonds ranging from 0.15 carats to 1.99 carats. The laboratory is also a take-in center for diamonds in larger sizes and other colors, as well as coloured stones and pearls, which are routed to GIA laboratories worldwide for servicing. The Mumbai laboratory also offers laser inscription and diamond sealing services. Grading reports are not issued for diamonds that have undergone unstable treatments, such as coating or fracture fi lling. And, while grading reports may be issued for diamonds that have been laser drilled, irradiated or HPHT processed, these treatments are prominently disclosed on the report.

GIA Professional Training – GIA’s Mumbai campus offers a wide variety of courses and instructional formats to meet the diverse needs of India’s jewellers and manufacturers. These formats range from on-campus programmes, lab classes, skill-building seminars and workshops, to customised corporate programmes, and online learning designed to minimize disruption to work schedules. Courses emphasize hands-on practical training, and include grading and identifi cation of diamonds, coloured gemstones and pearls; the detection of the latest treatments and synthetics; professional sales training and jewellery design. GIA courses are continually updated to ensure the most timely and accurate information and are taught in local languages throughout India.

To know more about GIA Laboratory Services or for more information about GIA education in India, call 1-800-102- 1566, email lab.giaindia@gia.edu / education.giaindia@ gia.edu or visit www.giaindia.in.