diamond colour treatments



Coating or painting a diamond is a primitive and easy way to improve or change the colour of a diamond. For a diamond with a slight yellow tint, a thin blue coating will neutralize this colour show and make the diamond appear whiter. Foiling involves putting a thin sheet of coloured foil behind a diamond in a setting to imporove or change the colour.

These treatments, although not common at all, are very easy to detect to a qualified gemologist. A 10x loupe is usually all that is required and signs to look out for include colour fade or concentration along facet lines, the colour appearing mottled and peeling of the colour. These treatments are non-permanent and will be disclosed on the diamond certificate.


Irradiation and heat treatment is used to change the colour of a diamond or to strengthen the already present colour in a diamond. Electron or neutron bombardment to the stone will change the atomic structure of the diamond to bring the desired colour. Other types of irradiation are also used, generally this type of treatment refers to the exposure of a diamond to radioactivity. Generally, a certain “type” of diamond will be treated in this way although this is not a strict rule. Spectrometers and other laboratory apparatus are used to detect this type of treatment. At IGR we specify whether a diamond has had this type of treatment on the certificate.


HPHT treatment involves subjecting a diamond to an environment of high pressure and high temperatures. This process will permanently change the colour of a diamond by altering it’s molecular structure. This process is usually difficult to detect and requires specific machinery to show whether a diamond has been subjected to this type of treatment.

At IGR we have the relevant tools to detect this treatment and will disclose this treatment on certificates where treatment is found.