Diamond Basics
Diamond Colour Enhancement: HPHT and Irradiation
High-pressure high-temperature processing and irradiation can alter a diamond's colour permanently, and both must be disclosed on grading reports.
HPHT treatment
High-pressure high-temperature (HPHT) processing can change a diamond's colour — for example, turning brownish stones colourless or producing fancy colours — by altering the crystal structure under extreme conditions similar to natural formation.
Irradiation and annealing
Bombarding a diamond with radiation, sometimes followed by heating, can produce fancy colours such as green, blue or pink. The resulting colour is permanent and safe to wear, but origin must be disclosed.
Why disclosure matters
Treated-colour diamonds sell for substantially less than natural-colour diamonds of the same visual hue, so a reliable grading report stating colour origin is essential before paying a fancy-colour price.
Buyer checklist
- ✓ Request a report that states colour origin as natural or treated
- ✓ Compare pricing against natural fancy colour benchmarks
- ✓ Ask for lab verification if origin is not already documented
Verification tools & references
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