Diamond enhancement
These include clarity treatments such as laser drilling to remove black carbon inclusions, fracture filling to make small internal cracks less visible, color irradiation and annealing treatments to make yellow and brown diamonds a vibrant fancy color such as vivid yellow, blue, or pink.
The CIBJO and government agencies, such as the United States Federal Trade Commission, explicitly require the disclosure of all diamond treatments at the time of sale.
Some treatments, particularly those applied to clarity, remain highly controversial within the industry—this arises from the traditional notion that diamonds hold a unique or "sacred" place among the gemstones, and should not be treated too radically, if for no other reason than a fear of damaging consumer confidence.
The size, color, and position of the inclusions are factors in determining the value of a diamond, especially when the other gemological characteristics are of a higher standard.
The development of laser drilling techniques has increased the ability to selectively target, remove and significantly reduce the visibility of black carbon inclusions on a microscopic scale.
Once the location of included black carbon crystal has been reached by the drill channel, the diamond is soaked in sulfuric acid.
After soaking in sulfuric acid the black carbon crystal will dissolve and become transparent (colorless) and sometimes slightly whitish opaque.
Under microscopic inspection the fine drill or bore holes can be seen, but are not distracting and do not affect sparkle or brilliance of the diamond.
The surface-reaching holes can only be seen by reflecting light off of the surface of the diamond during microscopic viewing such as a jeweler's 10x magnifying lens or loupe and are invisible to the naked eye.
The details behind the Yehuda process have been kept secret, but the filler used is reported to be lead oxychloride glass, which has a fairly low melting point.
The fracture-filling of diamond is a controversial treatment within the industry[citation needed]—and increasingly among the public as well—because some companies do not disclose this process when selling these stones.
Conversely, HPHT treatment is used to modify and remove color from either rough or cut diamonds—but only certain diamonds are treatable in this manner.
Sir William Crookes, a gem fancier as well as a chemist and physicist, was the first to discover radiation's effects on diamond color when in 1904 he conducted a series of experiments using radium salts.
Diamonds enveloped in radium salt slowly turned a dark green; this color was found to be localized in blotchy patches, and it did not penetrate past the surface of the stone.
[5] A diamond octahedron so treated was donated by Crookes to the British Museum in 1914, where it remains today: it has lost neither its color nor radioactivity.
These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers.
The annealing process increases the mobility of individual carbon atoms, allowing some of the lattice defects created during irradiation to be corrected.
In these natural stones the color is imparted by "radiation burns" in the form of small patches, usually only skin deep, as is the case in radium-treated diamonds.
[6] The application of colored tinfoil to the pavilion (back) surfaces of gemstones was common practice during the Georgian and Victorian era; this was the first treatment—aside from cutting and polishing—applied to diamond.
In 2001, however, NovaDiamond quit the HPHT gem business because of what the company's leader, David Hall, characterized as the underhanded practices of dealers.
Apparently, dealers were passing off NovaDiamond enhanced gems as naturally colored, and the company refused to be party to this deception.
Definitive identification of HPHT stones is left to well-equipped gemological laboratories, where Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy are used to analyze the visible and infrared absorption of suspect diamonds to detect characteristic absorption lines, such as those indicative of exposure to high temperatures.
Indicative features seen under the microscope include: internal graining (Type IIa); partially healed feathers; a hazy appearance; black cracks surrounding inclusions; and a beaded or frosted girdle.
