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Diamond Guide




Treatments Used to Improve the Color of Diamonds

Color affects diamond prices

A diamond's color—or lack of color—is one of the components that affects its value. Diamonds with the least amount of color, graded D, E, and F, are rare and command higher prices than diamonds with yellow or brownish tones.

On the other end of the spectrum, vivid, fancy color diamonds are even more unique, with price tags to reflect their rarity. So it's no wonder that the jewelry industry has developed methods to turn ho-hum diamonds into the show-stoppers that the public demands.

Turning yellow and brownish diamonds into gemstones with more visual appeal isn't a new idea, but some of the technology used to accomplish it is. Like other diamond treatments, only some of the methods used to enhance the stones are permanent.

Coatings & Other Color Tricks
Coatings applied to change a diamond's color are not permanent and are nearly always done to deceive the buyer.

  • Diamonds are sometimes coated with a substance that masks yellowish tints.

    Though it is applied with heat, the coating will eventually rub off with normal wear and cleaning.


  • Sometimes dots or larger areas of purple or blue ink are painted on the diamond to help counteract a yellowish color. The dots are usually obscured by the diamond's setting, so they are difficult to see in a mounted stone. This type of coating can usually be removed with water or cleaning solutions.

Irradiation & Heat Treatment
Irradiation, followed by a high heat treatment, can turn brown and yellow diamonds into fancy colored diamonds--greens, vivid yellows, blues, purples, reds and other colors. The color is usually permanent, but could possibly change if high heat is used during setting repairs.


  • Natural fancy colored diamonds are expensive and out of the reach of most buyers. A certificate from a respected grading lab should accompany all fancy colored diamonds that are marketed as natural.


  • Question the ethics of anyone who attempts to sell you a natural fancy colored diamond for a bargain price.


  • Treatment-produced fancy colors are affordable, and allow more of us to own a brightly colored diamond. They should not be considered an investment. Buy one because you love it, not because you think you can sell it for a profit later.


  • Ask the jeweler for care instructions when you buy an irradiated fancy color diamond.

High Pressure High Temperature Treatment (HPHT)
HPHT was first used to turn yellowish diamonds into fancy colored gemstones, but now it's also used to transform some brown diamonds into colorless diamonds that can be sold for a much higher price.

Some companies claim HPHT isn't a treatment at all, calling it a technique that finishes the job nature started. That attitude, and the fact that the process is difficult to detect, has made HPHT a controversial topic.

General Electric is producing colorless diamonds, called Bellataire, from type IIa diamonds that are nitrogen-free. The company has applied for a patent on the process used to transform the stones. On their Bellataire Web site, GE states:


    "BELLATAIRE Diamonds are extremely rare Type IIa diamonds that were originally crystallized without color and were destined to become extraordinary gems. During their journey to the surface of the Earth through volcanic pipes, though, these crystals were subjected to intense heat, tremendous pressure, and explosive turbulence. These conditions caused some molecular misalignment in these crystals, resulting in a brownish color and internal stress."

GE's position is that the process they use restores diamonds to their colorless state.

Gemological Institute of America (GIA) grading reports now indicate when HTPT treatments are detected by stating "HPHT Annealed" or "Artificially Irradiated" in the Origins portion of a report.


  • Only diamonds that are laser-inscribed with the words "HPHT PROCESSED," "IRRADIATED," or a specific registered name are graded.


  • GE uses a registration number and the letters "GE POL" to inscribe their diamonds.


  • There have been instances where inscribed lettering has been removed before a diamond was submitted for grading.

HPHT will continue to be a controversial topic, with grading labs trying to perfect ways to detect the always-improving process so that consumers can receive full disclosure about the diamonds they purchase.

Should you purchase an HPHT diamond? You're the only one who can make that decision. The diamonds are definitely gorgeous, but choosing between altered and natural is a very personal decision.

A few facts about HPHT Diamonds:


  • HPHT is permanent.
  • The Federal Trade Commission (FTC) requires that HPHT be disclosed.
  • Most HPHT diamonds are over .5 carats.
  • HPHT diamonds should cost less than similar natural diamonds.

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