identifying color enhanced diamonds

hpht treated diamonds
Fourier transform spectroscopy (FTIR) and Raman spectroscopy are used to analyze the visible and infrared absorption of suspected HPHT treated diamonds to detect characteristic absorption or emission lines, such as those indicative of exposure to high temperatures.

 These are two examples of colours produced by HPHT annealing
of type Ia diamonds. © GIA

 

irradiated diamonds

Prior to annealing, nearly all irradiated diamonds possess a characteristic absorption spectrum consisting of a fine line known as the GR1 line and an associated broad band. This is usually considered a strong indication of treatment. Subsequent annealing usually destroys this line, but may create several new ones; the most persistent of these is at 594 nm. If, however, an irradiated diamond is annealed above 1000°C, the 594 nm line is also destroyed, but leaves two new lines at 1936 and 2024 nm in the infrared. These lines are detected using spectrophotometers: the lines are best detected when the stone is cooled to very low temperatures (below -180°C).
It should be noted that some irradiated diamonds are natural. One famous example is the Dresden Green Diamond. Naturally irradiated diamonds also possess the GR1 line.

These are typical examples of colours produced by irradiation or irradiation followed with a heat treatment. Most of the samples in this picture underwent a heat treatment after irradiation. © GIA

 

coated diamonds
With a borazon needle (Mohs scale hardness of 9.75), a coating can be easily scratched and thus a fake can be unmasked by relatively simple means. However, in some rare cases, the diamond may be damaged as well. The dyes may be removed in hot water or alcohol, while vacuum-sputtered films are simply removed by dipping the diamond in sulfuric acid. The films can be detected by worn areas where the coating has been scratched off or by differential interference contrast (DIC) microscopy. With this latter technique, elevations on the surface in the order of a few hundred nanometers (1 nm = 0.000001 mm) can be detected, enough to detect any thin coating on the surface of a diamond.

The intense pink colour of this diamond as a result of surface coating. © GIA