Professional Jeweler Archive: Judging Fancy-Color Diamonds: Is the Color Natural?

December 2002


Judging Fancy-Color Diamonds: Is the Color Natural?

Part 3 of our series discusses color treatments

Last month, we talked about how to judge the purity of color, depth of color (tone and saturation) and color distribution throughout colored diamonds. But in addition to a rainbow of colors that occur naturally, diamonds can be transformed by treatments into beautiful, desirable colors using several techniques. Radiation has been used for many years to change tinted, off-white diamonds into various shades of yellow, blue and blue-green, and in most cases can be easily distinguished from the natural by any competent gemologist. But new techniques are creating new challenges, and determining whether color is natural may require very sophisticated, high-tech procedures only available at a major gem testing laboratory.

HPHT Processes

Most retailers are now aware of the relatively new technique known as “high-pressure, high-temperature annealing” that is being used to transform very off-white and brownish diamonds into “colorless” and “near colorless” stones. This technique is also used to transform these diamonds into a variety of “fancy” colors, from yellowish-green and greenish-yellow to exquisite shades of pink and blue. While the yellowish-green and greenish-yellow diamonds often have a distinctive look that sets them apart from most diamonds of comparable natural color, this is not the case with pink and blue, which are very difficult to distinguish from the natural.

Since natural fancy-color diamonds can be costlier than “colorless” diamonds – and fancy-color blue and pink diamonds much costlier because of their rarity – I recommend against selling any such diamond represented as having natural color without a current laboratory report; if it lacks one, be sure to obtain one. Today, most major labs will grade diamonds treated in this manner, indicating the treatment in a special comment on the report.

There is nothing wrong with selling a diamond that has obtained its color through some form of treatment. Increasingly, fine jewelry designers are using color-treated diamonds to create distinctive jewelry at very attractive prices. But it is important to know whether the color is natural or the result of some treatment process so you know you have paid an appropriate price.

The information presented here is an excerpt from Diamonds: The Antoinette Matlins Buying Guide and is reprinted with the permission of the publisher, Gemstone Press (Woodstock, VT). For more information about the book, call Gemstone Press at (802) 457-4000 or visit

Extra Word of Caution on Pink and Blue Diamonds

Anyone considering the purchase of a diamond represented to be natural blue or natural pink must be sure it is accompanied by a current
report issued by a major laboratory after December 2000. If the date on the report is earlier than that, ask your supplier to resubmit the diamond to a major laboratory for verification, or make the purchase contingent upon getting this documentation.

Most laboratories were unaware of the use of HPHT techniques to create blue and pink diamonds until 2000, and diagnostic data with which to detect the treatment were not available until later that year.

Because standard “routine” testing would not have detected the treatment, earlier reports may not be accurate.

The treated color in the red heart and octagonal natural diamonds is achieved by irradiation and controlled annealing. Even treated reds are considered rare because the color is very hard to achieve. Diamonds are courtesy of Nice Diamonds Inc., New York City. Photo by Robert Weldon.
Much like their natural color counterparts, green treated diamonds like this one owe their color to irradiation. Diamond is courtesy of Nice Diamonds Inc., New York City. Photo by Robert Weldon.
Treated blue diamonds like this one owe their color to irradiation rather than natural blue diamonds, which owe their color to the presence of boron. In general, the treated colors are far more saturated than in natural color diamonds. Diamond is courtesy of Nice Diamonds Inc., New York City. Photo by Robert Weldon.

Copyright © 2002 by Bond Communications