Determination of colour authenticity of diamonds

Following the determination of the nature of a coloured diamond (synthetic or natural), the colour authenticity is tested. Treatments applied to fancy coloured diamonds tend to improve their colour. These treatments consist either in coating the surface with a coloured substance, or in irradiating the whole or part of a diamond. This last treatment is the most common and is generally followed by a heat treatment (annealing).

Diamonds with a reduced colour (high-pressure high-temperature treated diamonds) are disclosed as Treated Diamond.

In order to determine whether a diamond is of natural or artificial colour, the following
investigations are routinely performed on loose stones:

• Thorough observation with a binocular microscope in dark field, transmitted light, polarized light, and immersion (if necessary)
  
• Quick test with a spectroscope
  
• FTIR spectroscopy to determine the type of diamond (type IaA, IaA/B, IaB, Ib, IIa, IIb), the presence or absence of C-H stretching bonds and the presence or absence of irradiation/annealing absorption peaks (H1b, H1c) and other infrared characteristics.
  
• UV-visible-near-infrared spectroscopy of the diamond, cooled down to approximately -130°C.
• Photo-Luminescence spectroscopy of the diamond, cooled down to approximately -130°C.

SSEF uses the widely accepted trade terms to disclose fancy colour diamond grades if their
colour is natural:

• faint
  
• very light
  
• light
  
• fancy light
  
• fancy
  
• fancy intense

Reports for natural coloured diamonds are issued on GEMSTONE REPORTS stating

• Weight
  
• Shape and Cut
  
• Measurements
  
• Colour
  
• Identification
  
• Comments concerning the colour authenticity of the diamond
  
• Colour photo of the stone

For more information, please refer to our STANDARDS & APPLICATIONS catalogue.