NOTE: Due to the increase and improvement of synthetic and enhanced “white” and coloured diamonds, no appraisals of coloured diamonds or major diamonds will be done without a laboratory report from a qualified lab such as GIA or AGS confirming the nature of the stone and/or colour origin.
Gemstones have been treated to enhance clarity and primarily colour since antiquity. The most common forms for treatment have been heat and dying. Diamonds have also been enhanced through the years. Back in the day, irradiation was common for turning stones from off-colour to intense blues and yellows. With the increasing popularity of coloured diamonds, this is still a treatment used today.
Fracture filling or clarity enhancement is another treatment used to lessen the appearance of inclusions. The filling is considered permanent for normal wear and cleaning. The process takes place under extreme pressure and is done where a feather breaks the surface or can be done after laser drilling. Care must be taken however, when repairing a piece of jewelry with clarity enhanced stones. The heat from a jeweler’s torch will nullify the treatment and the stone would have to be refilled.
A more recent treatment that is much more difficult to detect is HPHT which is High Pressure High Temperature. This was first announced in 1999 by General Electric and Lazare Kaplan International. This treatment is primarily used to improve the colour of diamonds by lightening them from tinted, usually brown to whiter or colourless but can also be used to turn stones into fancy colours.
The brown color in diamonds is caused by mechanical stresses at elevated temperatures while still deep within the earth. This causes their crystal lattices to become deformed in a process known as plastic deformation. This process begins the induction of linear defects into the crystals, which are known as dislocations.
When a diamond crystal is subjected to very high temperatures, the structure of the dislocations is modified, causing the brown coloration to be reduced or lightened. Conversely, at these very high temperatures, diamonds will convert to graphite unless very high pressure is also applied. This is done using the same kind of equipment in which diamonds are synthesized from “scratch”. Use of such extreme conditions is not without its dangers. There is always the danger that inclusions and fractures can be exacerbated, the stones can break and the surfaces can become frosted and pitted. If the brown coloration is reduced sufficiently by HPHT treatment, the result is a colourless, near-colourless or sometimes a pink diamond. In rarer stones, if boron is present a pale blue color can be produced by HPHT treatment.
Less than 1 percent of natural diamonds are type II of adequate quality to be suitable for HPHT treatment. In other brown diamonds, HPHT treatment produces particular nitrogen-containing defects which give rise to a fancy yellow to greenish-yellow color, often with strong green fluorescence.
What does this mean to you as a potential diamond owner? When purchasing any diamond but particularly a fancy coloured one, only buy with an accompanying report from a nationally known laboratory such as GIA or AGS. These treatments are very difficult to detect with the normal equipment used by most appraisers. It is imperative that you know exactly what you have. Yantz Bradbury Associates will not appraise any coloured diamond cut to modern proportions without a report attesting to the colour origin.
Yantz Bradbury Associates
P.O. Box 10123 – Rockville, Maryland – 20850
Office: (301) 335-6687
Serving MD, VA and DC Metro Area