Sign up for our newsletter |

Home Page


Pink Scare

When EGL was first asked to test the new hard-coated pink (and orange) diamonds, they were told the stones owed their deep colors to a process call "infusion." The word evokes "diffusion," a process generally reserved for chemically coated gems that have been heated to high temperatures so that trace element additives will dissolve, penetrate the surface, and trigger a color change as they interact with the chemicals in the stone. Diffusion usually creates a thin rind of color around the entire stone which is, technically speaking, a part of its atomic structure. True, the color may only be skin deep, but it is, molecularly speaking, a part of the stone. The term "diffusion" says as much.

Coatings, by their very nature, are affixed to gems, usually on the pavilion where light reflection spreads the color they produce into the crown. These coatings, which both GIA and EGL found to be composed of alternating layers of SiO2 and metallic compounds, are no exception. No matter how durable and tightly bonded, they are extrinsic. Both GIA and EGL found that the new thin-film color coatings on the diamonds they tested had not infused beneath or into the surface. "Use of the term ‘infused' is clearly not appropriate," Deljanin says. What is, I asked? "‘Coated,'" I am answered.

Begging Big Questions

As long as they are accompanied by identification papers from leading gemological laboratories, the new coated diamonds do not pose any kind of threat from a standpoint of deception. Further, no recognized lab that we know of is issuing grading reports for these diamonds. Currently, gemologists frown on grading diamonds that owe their looks to an unstable treatment. But what if the treatment were stable? Would these diamonds then qualify for color, clarity, and cut grading?

A year ago, such a question would not have been raised. But now that most leading labs have decided to issue grading reports for synthetic diamonds, one has to wonder if this privilege—once reserved for natural diamonds alone—will be extended even farther to stones with permanent treatments. One thing for certain: The dividing line between natural and synthetic—as well as natural and treated—diamonds is shrinking fast.

So the question of grading coated diamonds is of more than theoretical interest. EGL reports that some coated diamonds have been submitted to labs as HPHT (high pressure, high temperature) treated. Since such diamonds are now entitled to grading reports, the use of this term with hard-coat color-improved diamonds is understandable. That's why the trend to use language to legitimize treatments has some jewelers worried.

"I don't care how scuff and scratch-resistant a coating is," says Jim Adair, a jeweler in Missoula, Montana, "you're talking about something that is essentially like mylar bonded to a diamond's surface. I see no room or reason for such stones in any jewelry store. This is going to come back to bite us—hard."

purple-pink coated diamond
Face up: A 4.02 carat purple-pink coated diamond.
diamond under microscopic testing
EGL USA reports that in some coated cases, under standard microscopic tests, the body color was found to be uneven on both the crown and pavilion, and a few diamonds exhibited a lack of color in nicks on facet junctions.
diamond lost color from coating substance
EGL USA found that at higher temperatures of 900 to 1200ºC, the color was lost from the coating substance.
pink diamond
Surface treated: A 0.52 carat coated pink diamond.
two coated diamonds before boiling in sulfuric acid
Two coated diamonds before (ABOVE) and after (BELOW) boiling in sulfuric acid. All the coated diamonds reverted to their presumed original light brown color after being boiled for a few minutes, reports EGL USA.
two diamonds after boiling in sulfuric acid