Black diamonds are relatively rare in nature and has been introduced for jewelry since the end of 1990s and it comes naturally and artificially. It has been known that the natural black diamond contains inclusions such as granular or needle-like graphite or sulphide minerals. The artificial black diamond is known to be produced mainly by neutron irradiation in a nuclear reactor, however, this black Colour is actually deep blue to green. Recently, a new type black diamond has been produced by the high temperature (HT) treatment using diamonds of very poor quality single crystal or polycrystalline diamonds. The Colour of diamond can be changed to black by graphitization on the surface and/or crack-like defects reaching to the surface. In this work, we produced black Coloured diamond by N ion implantation and heat treatment in vacuum or inert gas atmospheres.
Determining origin of Colour for some green diamonds still poses a great challenge for the gemologist. The green Colour is usually caused by irradiation, but the source of the radiation may be either natural or the product of a laboratory. Some have features that are unlike those typically seen in diamonds treated by cyclotron or lower-energy electron irradiation in a linear accelerator. The distinctive feature around the culet of this irradiated diamond (commonly referred to as the umbrella effect) is a result of the cyclotron. Lower-energy electron irradiation in a linear accelerator can create a thin layer of Colour beneath the pavilion facets. These days, the most common methods are neutron irradiation in a reactor and high-energy electron irradiation in a linear accelerator. These can completely penetrate even large stone, the resulting green Colour was created more uniformly throughout the diamond rather than near the surface. The Hanmi laboratory very recently examined very rare type green diamond that showed some interesting features. The 7.69ct diamond (12.38x10.30x6.89 mm) was Colour graded as Fancy bluish green. Colour concentration pattern was uniformly throughout the diamond. UV-Visible spectrum showed a GR band with the GR1 at 741 nm, thus, the green Colouration was due to an irradiation. Infrared spectroscopy revealed that this was a type_II_a diamond with peak at 1414cm-1. However, we would not conclude whether the diamond is of natural or artificial Colouration.