HPHT Color Treatment (7.40)
General Electric and LKI (Lazare Kaplan, Inc.) developed the method of HPHT (high pressure high temperature) to lighten or intensify color in natural diamonds -- type IIa browns -- trademarking it “Bellataire” (formerly Pegasus) came to market in March, 1999. This newest scare and sensation had many people in the business concerned, due to its non-detection by several labs in the U.S. to which LKI submitted their newest treatment.
Producers of the HPHT color enhanced diamonds laser inscribe the girdles to make sure the that disclosure is apparent.
The above image is courtesy of: https://www.ssef.ch/identification-of-colourless-hpht-treated-diamonds-e-g-ge-pol/
Identification: Since the treatment is permanent and stable GIA will do a lab report on this type of treated diamond and add a laser inscription on the girdle (if not already present), to make sure it is fully disclosed which is required in the trade. HPHT treatment is also used in creating lab-grown diamonds which we will delve into in section 8.
After checking for any laser inscriptions that might identify it as such we must determine the type. As with lab-grown diamonds, identifying the type (also discussed section 8) is first on the check list.
HPHT-color-treated are natural in atomic structure so they cannot be identified with the basic tools such as thermal or electrical testers.
Identify the diamond type: The HPHT color-lightening process is only effective on the less common Type IIa and rarely Type IaB diamonds. Therefore, the first step is to use Fourier Transform Infrared (FTIR) spectroscopy to determine if a diamond belongs to one of these types.
Photoluminescence Analysis: The standard detection methods will include a spectroscope (spectrophotometer) along with photoluminescence analysis. A high-intensity laser is applied to the diamond whereas the energy from the laser's photons is absorbed by electrons, causing them to jump from their ground state to a higher excited state.
As the electrons return to their lower energy state during the relaxation stage new photons are released known as luminescence.
Using the FTIR spectroscope the emitted light is recorded and plotted on a photoluminescence spectrum, which reveals the intensity of the light versus its wavelength. A key principle is that the emitted photons have a longer wavelength (lower energy) than the absorbed laser photons, a phenomenon called a Stokes shift.
Remember HPHT color treated diamonds will be valued at a significant discount below its natural untreated counterpart.
For a closer and sharper view at the wavelength bands a liquid nitrogen immersion environment is also used in spectroscopy.
The above images are courtesy of: https://www.gemmoraman.com/detecting-hpht-treatment-of-natural-type-iia-colorless-diamonds/#:~:text=There%20is%20no%20single%20tool,Raman%20spectrometer%20such%20GemmoRaman%2D532.