 July
22, 2002 - GIA documented a new laser treatment in the Summer 2000
issue of Gems & Gemology (pp. 138–146). The purpose of
this treatment, as with typical laser drill holes, is to provide a
path for acid solutions to bleach dark, totally internal inclusions.
By focusing a laser beam on or near such an inclusion, the technician
creates feathers (cleavages) or enlarges existing ones so that they
extend to the surface of the faceted diamond. Within the feathers one
can see irregular lines or channels (black or white, often with a sugary
or frosted appearance) that have been left behind by the laser. In
most of the earlier examples, the treatment is fairly obvious when
the diamond is examined with magnification.
Recently, in GIA's laboratories on both coasts, they have encountered
a number of feathers that have small, white, disk-like or tabular
areas with irregular outlines and a sugary texture (see figure),
rather than the channels described above. These tabular features
are located in the same areas of the fractures where we would expect
to see the more obvious irregular channels. The “tablets” are visible
when one looks perpendicular to the plane of the feather, and they
are practically invisible when the viewing direction is more parallel
to the feather.
The fact that we have seen these unusual features in a large number
of diamonds clearly indicates that they are being created by design.
These tabular characteristics are more difficult to recognize than
the irregular channels noted earlier in laser-induced feathers, which
makes this treatment more challenging to detect. It is, therefore,
very important to use high magnification and various light sources
to check all surface-reaching fractures that extend from totally
internal inclusions. |
The causes of these colours lies at atomic level. Diamond comprises covalently
bonded carbon atoms. In pure diamond visible light does not possess enough
energy to excite electrons in the bonds and consequently no light is absorbed
in the visible band and all the light falling on the diamond is transmitted
and refracted back to the eye causing the diamond to appear completely colourless.
However, most diamonds are not perfect. The diamond lattice contains impurities
such as nitrogen and the lattice is sometimes defective with a missing atom.
This presence of impurities, or more specifically the electrons associated
with the impurities, is the cause of colour in the majority of diamonds.
The rarety and subsequent high value of fancy coloured diamonds has led to
the development of artificial colouration of diamonds.
There are two main types:
Cyclotron Treatment:
This is a device used to accelerate sub atomic particles such as protons, deuterons
(heavy hydrogen), and alpha particles (Helium nucleus mass 4, charge +2e)
and smash them into the diamond lattice. The colour produced is from dark
green to almost black. The particles are charged and depth penetration is
poor, forming a skin. The colour is permanent unless the stone is repolished.
Further heating converts the green to yellow, orange or brown.
Electron Treatment:
Electrons are accelerated in to the diamond, again only skin deep and produce
a blue to blue/green colour. heat treatment produces orange-yellow, pink-
mauve, and brown.
Gamma Ray:
Not used today due to its slow effects taking months to colour a stone. Produces
permanent blue and blueish-green colours.
Neutron Treatment: 
This is the most common form of irradiation used today. The diamonds are bombarded
in a nuclear reactor and produce permanent green. When heated, yellow, orange,
brown, pink and mauve colours may be produced.
Radium:
Produces colours from alpha, beta, and gamma radiation, but is not used as
stones are left radioactive.
Evidence of treatment:
If you should ever consider buying a coloured diamond have it checked by
a reputable laboratory to ascertain whether the colour is natural or
otherwise. The difference in price is substantial. A report may also
indicate its permanance.