Coatings are not permanent and are typically done to deceive the buyer. The diamond may be coated with a substance to mask yellowish tint or have an area of dark ink painted strategically under the setting to counteract the yellowish color. Some coatings may be applied with heat but will eventually rub off with normal wear and cleaning.

Color Enhancement

The most well-known color enhancements are HPHT and Irradiation. Although color enhanced diamonds may be accepted by the GIA for grading, the FTC requires that such treatments be disclosed on the grading report.  The AGS will not grade color enhanced diamonds.

Whiteflash will not sell color or clarity enhanced diamonds.

High Pressure / High Temperature Treatment (HPHT)

General Electric developed the High Pressure/High Temperature (HPHT) annealing method for artificially influencing a diamond’s natural color. It was first used to turn yellowish diamonds into fancy colored diamonds, but now it is also used to improve the color of unpopular yellowish-brownish diamonds.

In 1999 the GIA began accepting these diamonds for grading. They were involved in research with GE at the time. The Federal Trade Commission requires that HPHT must be disclosed, so GIA notes "HPHT Annealed" or "Artificially Irradiated" on grading reports when it is detected. The diamonds themselves are laser-inscribed with the words "HPHT Processed," "Irradiated" or a specific registered name so there is full disclosure. "GE POL"has been inscribed on Bellataire diamonds.

GIA’s reasoning is as follows: "/diamonds_info.by grading them in the lab, we were able to indicate that they were HPHT annealed on their reports (and on the diamonds themselves). Our “greater good” goal was to protect the trade and the public by protecting the integrity of all diamonds/diamonds_info."

Whether such diamonds should be considered 'treated' is a controversial issue. The Bellataire diamond began as GE/POL (General Electric/Pegasus Overseas Ltd). Bellataire developed a marketing campaign proclaiming that the annealing process was ‘restoring’ diamonds to their natural color, rather than artificially influencing their existing color. Bellataire maintains that since the GIA does not issue grading reports on treated diamonds theirs don't fall into this category. They generally hold the minority opinion: Many view such color treatment as an unnatural enhancement, like clarity enhancements (laser drilling & fracture filling).

Irradiation

Usually associated with fancy colors, exposing the diamond to radioactivity can turn brown and yellow diamonds into green, vivid yellow, blue, purple, red and other colors. Afterwards, high heat treatment may be used to stabilize the new color. This is usually permanent, but could possibly change if high heat is used again in the future; during setting repairs for instance. Only a small percentage of diamonds can be successfully improved using these methods.

Whether you are a fan or not - as long as treatments are disclosed it's up to the buyer to decide if it is acceptable, and to enjoy wearing the diamond.