High Pressure High Temperature
Diamond Color Treatment (HPHT)
Fancy colored diamonds are more popular than ever, so gemologists have developed ways to create affordable versions by treating diamonds in a lab. Treated diamonds are natural diamonds that started out with an unappealing or slightly off color. By exposing these less desirable diamonds to the same high-tech alchemy used to create synthetic colored diamonds, the apparent color and appearance of these diamonds can be significantly improved. Irradiation, followed by a high heat treatment, turns brownish and yellow diamonds into fancy colored diamonds of all hues. The color of some diamonds can be dramatically changed by using HPHT diamond color treatments. Recently, we have seen HPHT color treated diamonds with vibrant yellowish green, radiant red and deep blue colors enter the market. Diamond color treatments make it possible for more people to own a vivid fancy colored diamond because most natural fancy vivid colored diamonds are very rare and extremely expensive. Choosing between color treated diamonds and natural diamonds is usually a monetary decision.
HPHT diamond color treatment was originally used to turn yellowish “off color” diamonds into fancy colored diamonds, but now it is also used to transform some unpopular brownish diamonds into the more expensive colorless diamonds. The fact that the process is so similar to nature and very difficult to detect has made HPHT diamond color treatment a controversial topic in the diamond industry. The process heats the diamond to about 3,600 degrees Fahrenheit while the diamond is under the extreme pressure of 60,000 atmospheres. The pressure is needed to stabilize the process and enable the diamond to heal any dislocations and promote the growth of crystal structures. The result of healing these natural dislocations in the diamond’s crystal structure is a reduction in the brownish color. Because of the heat and pressure of the HPHT diamond color treatment process, most HPHT color treated diamonds are larger than .50 carats; the smaller diamonds just cannot handle the process and implode or burn up.
To detect the difference between a natural colored diamond and a HPHT color treated diamond, you would have to freeze the diamond with liquid nitrogen; then excite the cryogenically cooled diamond with a laser to see what colors appear. Last, you would use a spectrometer to measure to the nanometer the difference in light absorption patterns and excitation peaks. Or you could just ask to see the Origin of Color on the diamond certificate.
The diamond grading labs are perfecting ways to detect the HPHT diamond color treatment so that consumers can receive full disclosure about the diamonds they purchase. If HPHT diamond color treatments are detected, Gemological Institute of America (GIA) grading reports now state "HPHT Annealed" or "Artificially Irradiated" in the Origin of Color portion of a report. Only HPHT color treated diamonds that are laser-inscribed with the words "HPHT PROCESSED," "IRRADIATED," or a specific registered name (GE for example) are fully graded by GIA.
Since 1999, European Gemological Lab (EGL USA) has been profoundly involved in the HPHT diamond color treatment’s research and development. As colorless diamonds and fancy colored diamonds modified by HPHT diamond color treatments have proven to be stable to normal wear, EGL USA began grading these permanent color treated diamonds in January 2000. They were the first gemological lab to design a grading report especially for colored HPHT treated diamonds.
The facts about High Pressure High Temperature color treated diamonds:
- HPHT diamond color treatment is permanent.
- The Federal Trade Commission (FTC) requires that any diamond color treatment be disclosed.
- Most HPHT color treated diamonds weigh over .50 carats.
If you question a diamond color's origins, ask for the gem lab certificate to verify its color as natural. HPHT color treated diamonds should cost significantly less than natural fancy color diamonds. For example, a GIA certified natural .50ct VS2 vivid fancy green colored diamond will sell for $50,000 per carat, whereas a .50ct VVS2 vivid fancy green HPHT and irradiated diamond will sell for $3,000 per carat. Even though the VVS2 diamond has a higher clarity, it costs less because it was color treated. Although color treated diamonds and synthetic diamonds can be just as beautiful as their natural counterparts, the origin of their color should be fully disclosed by the seller. Ethical practice and the law require that synthetic diamonds and any diamond color treatments be fully disclosed to consumers.
Synthetic Fancy Colored Diamonds
Synthetic fancy colored diamonds are another affordable option. Synthetic fancy colored diamonds are real diamonds, created in a lab and introduced to different trace elements, such as nitrogen for yellow diamonds, boron for blue diamonds, or radiation for green, during the diamond forming process to create their vivid colors. Synthetic fancy colored diamonds make owning a vivid fancy colored diamond a reality for those who cannot afford a natural fancy color diamond. Remember, a diamond is a diamond whether nature made it or if man created it in a lab.
Synthetic diamonds are produced each year at nearly four times the rate of natural diamonds. About 130 million carats of diamonds (29 tons) are mined annually, and about 100 tons of diamonds are created in a lab annually. However, the vast majority of synthetic diamonds produced are small, imperfect diamonds suitable only for industrial-grade use. Industrial diamonds are used as an abrasive in sandpaper, or they are embedded in steel drill bits and saw blades. 
