Researchers have made countless efforts to intensify or remove color in diamonds. They've had more success with attempts to add or enhance diamond color than with those to remove color. Either way, all the processes fall under the general heading of treatments. A treatment is any human-controlled process that improves gem appearance. Gem treatments generally improve apparent clarity or enhance or remove color.
Some treatments are completely legitimate and some are questionable. Most treated diamonds are presented honestly. But a treated diamond might reenter the market if a long time owner wants to sell it, or if someone inherits the diamond with no knowledge of its history. The fact that it was treated might be forgotten or unknown. If it's also undetected, it might be presented as a natural color diamond.
The equipment available in a typical retail store can't positively identify many of today's diamond color treatments. However, laboratory gemologists working with the proper equipment can detect them. That's why an appraisal and certificate is important: It can assure you of a legitimate transaction.
The seller of a treated stone is responsible for honestly and accurately representing it treatment history. There are no allowances for lack of training, equipment, time, or opportunity to determine the origin of color.
Adding and Enhancing Color
Diamonds can be treated to alter or add color by coating, irradiation, heating, or by a combination of irradiation and heating. Efforts to add color range from the primitive to the highly sophisticated. One of the earliest color treatments was coating. Most coatings were super thin layers of chemicals applied to a few of the pavilion facets, or to a tiny spot on the culet or around the girdle.
If the stone remains in its mounting, a coating can go unnoticed for years. Then it might be discovered of the stone is repolished, which usually removes the coating.
Early coatings were not very durable. Modern technology, however, has produced tougher coatings, similar to t hose used on camera lenses and optical instruments.
Coatings aren't very common, and might be difficult to detect. At a major auction house in the 1980s, someone switched a valuable pink diamond with a very pale yellow one that had been coated with pink nail polish. Careful attention caught the deception before the auction took place.
It's a good idea to check for coatings when you take diamond jewelry in for repair. Experienced diamond professionals often sense immediately when something about a color doesn’t look right. The color might appear unnatural and hard to classify. Revealing the coating is t hen a matter of patient, careful examination with a microscope. When in doubt, send any questionable stone to a lab for confirmation.
While coatings are confined to the surface of a stone, and are easy to remove or damage, irradiation penetrates the stone. It changes the color by altering the crystal structure of the diamond, so it's more permanent than a coating.
The irradiation process dates from about 1904, when british scientist Sir William Crookes buried some diamonds in radium salt for a year. As with diamonds exposed to radioactive rock in the ground, Crookes' diamonds turned green. But they also became radioactive. This hazard has been overcome since then by advances in radiation treatment. From time to time, however, dealers and retailers who specialize in antique jewelry still encounter radioactive diamonds.
Modern radiation treatments are byproducts of the nuclear age. Technicians can now duplicate most natural diamond colors. Color-treated blue-greens, yellowish greens, yellows, browns, and oranges were the first to be readily available. Now even rare colors like pure blues, purples, pinks, and greens, can be treatment included. Irradiated diamonds have become common and accepted alternatives to the more valuable natural fancy-colored diamonds.
Annealing, or heating, can influence the color of some diamonds, but it’s often used to stabilize irradiated color. Heat can also be combined with high pressure to induce color.
Removing Color
Until the late 1990’s, efforts to remove color from diamonds were not very successful. That changed in March 1999 when Lazare Kaplan International (LKI) announced that it had worked with General Electric (GE) scientists to develop a process to improve the color in some diamonds in the normal color range.
This process uses a combination of high pressure and high temperature – the same critical forces in diamond formation – to lighten or remove diamond color. After treatment, the color of the treated diamonds usually falls between grades D and H.
LKI markets these diamonds under the brand name Bellataire. To help the jewelry industry identify and disclose them, the company applies a laser inscription to each diamond’s girdle. The earliest inscriptions said “GE POL” (POL is an acronym for Pegasus Overseas Limited, an Antwerp-based subsidiary of LKI that’s the exclusive agent for these diamonds). Now, each diamond is inscribed “Bellataire”.
While gem labs won’t grade diamonds that have been subjected to certain treatments because the effects of the treatment are not permanent, it does grade Bellataire diamonds – and notes the fact of the treatment on the report.
Today, many companies worldwide use high pressure, high temperature treatments to remove diamond color and also, in rare cases, to create fancy diamond colors like green, yellow, blue, and pink.
