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Some irradiated diamonds are completely natural; one famous example is the Dresden Green Diamond. [11] In these natural stones the color is imparted by "radiation burns" (natural irradiation by alpha particles originating from uranium ore) in the form of small patches, usually only micrometers deep. Additionally, Type IIa diamonds can have ...
Diamond color is graded by comparing a sample stone to a master stone set of diamonds. Each master stone is known to exhibit the very least amount of body color that a diamond in that color grade may exhibit. A trained diamond grader compares a diamond of unknown grade against the series of master stones, assessing where in the range of color ...
Most gem diamonds are traded on the wholesale market based on single values for each of the four Cs; for example knowing that a diamond is rated as 1.5 carats (300 mg), VS2 clarity, F color, excellent cut round brilliant, is enough to reasonably establish an expected price range.
Cyclotroned diamonds have a green to blue-green color confined to the surface layer: they are later annealed to 800 °C to produce a yellow or orange color. They remain radioactive for only a few hours after treatment, and due to the directional nature of the treatment and the cut of the stones, the color is imparted in discrete zones.
C centers impart a deep yellow to brown color; these diamonds are classed as type Ib and are commonly known as "canary diamonds", which are rare in gem form. Most synthetic diamonds produced by high-pressure high-temperature (HPHT) technique contain a high level of nitrogen in the C form; nitrogen impurity originates from the atmosphere or from ...
Type IIa diamonds can have their structural deformations "repaired" via a high-pressure, high-temperature process, removing much or all of the diamond's color. [5] Type IIa diamonds constitute a great percentage of Australian production. Many famous large diamonds, like the Cullinan, Koh-i-Noor, Lesedi La Rona, and The Lulo Rose are Type IIa ...
The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. A clarity grade is assigned based on the overall appearance of the stone under ten times magnification, which is the standard magnification for loupes used in the gem world.
Diamonds are mainly irradiated to become blue-green or green, although other colors are possible. [27] When light-to-medium-yellow diamonds are treated with gamma rays they may become green; with a high-energy electron beam, blue. [21] The difference in results may be caused by local heating of the stones, which occurs when the latter method is ...