THE NEWS BULLETIN

GIA Announces Refinements for Fancy Colours

By: John M. King, James E. Shigley and Robert C. Kammerling

GIA Gem Trade Laboratory, Gemological Institute of America

The GIA Gem Trade Laboratory (GIA GTL) has made important refinements to its system for colour grading coloured diamonds. To help disseminate this information to the trade, the following report has been developed from the article "colour Grading of coloured Diamonds in the GIA Gem Trade Laboratory," by John M. King, Thomas M. Moses, James E. Shigley, and Yan Liu. It was published in the Winter 1994 issue of Gems & Gemology (Vol. 30, No. 4, pp. 220-242), the quarterly journal of the Gemological Institute of America. Readers are encouraged to obtain and read the original article on this subject. Additional topics in the article include a brief history of diamond colour grading at GIA GTL, some basic colour science concepts, GIA GTL colour terminology for coloured diamonds, and a note on some special situations encountered in describing coloured diamonds.

One of the primary goals of the GIA Gem Trade Laboratory is to support the diamond industry through services that help protect the trade and facilitate business. Particularly significant to the trade today are coloured diamonds. Two important concerns with these diamonds are their colour origin--that is, whether their colour is natural or laboratory treated--and their colour description or grade. As part of its ongoing research and development efforts in the area of colour, GIA GTL has recently announced improvements to its system for colour grading fancy colour diamonds. These improvements represent refinements to the long- established system which in its essentials remains unchanged in concept and application. So that members of the trade could better understand these refinements, GIA GTL decided to explain the concepts on which the colour grading system is based through the article cited above.

Why the Refinements? Until fairly recently, coloured diamonds were encountered infrequently in GIA GTL, as in the trade. Today, however, increasing numbers, and a broader variety of colours, are seen. One reason for this is the Argyle deposit in Western Australia, which has brought many more coloured diamonds to the marketplace during the last decade. Some of these diamonds, such as the intensely coloured pinks, command high prices. In addition, recent auction sales have spurred interest in coloured diamonds--and these well-publicized sales have generated a number of articles in the trade press. Recognizing that a system to communicate the colours of these diamonds clearly and consistently is vital for effective commerce, GIA GTL undertook a comprehensive re-evaluation of its system.

Importance of Standard Procedures Clearly, standard procedures must be established and followed if coloured diamonds are to be graded effectively and consistently. In the GIA GTL system, colour science methodology is used as the basis for these procedures. At the same time, sensitivity must be maintained to both the unique properties of coloured diamonds and GIA GTL's 40-year history of grading these stones. Among the factors that must be taken into consideration during colour grading are the following:

* A consistent, standard source of light with known illumination characteristics

* An appropriate visual environment for grading

* The "geometry" between the positions of the light source, the diamond, and the observer

* The use of standard colour reference materials for colour comparison

* The normalcy of the colour vision of the observer * The language used to describe colour

* The relationships between the chosen colour terms

To address these factors, GIA GTL uses a standard light source, viewing environment, and viewing "geometry"; in addition, all graders are tested to establish that their colour vision is "normal." For the actual colour grading of coloured diamonds, we follow a basic three-step procedure: First, we determine the face-up colour to be described (referred to as the "characteristic" colour). Next, we locate the position of that colour in relation to other colours by using known reference comparators. Last, we select appropriate terminology to describe that colour. This process uses colour grading concepts similar to those applied when grading near-colourless to light yellow (or brown) diamonds on the D to Z colour scale; for example, in most cases boundaries are marked with diamond masterstones, colour terms are applied to ranges of colour appearances, and controlled side-by-side visual comparisons are made. Unlike D to Z grading where stones are judged primarily in the table-down position to establish the relative absence of colour, the fancy colour grading system judges the relative presence of colour in the face-up position.

New Fancy Grades

To strengthen the already-established system, GIA GTL has expanded the use of its Fancy-grade terms to all hues and has introduced two new Fancy-grade terms--Fancy Deep and Fancy Vivid--to better address areas of strong colour. The other GIA GTL Fancy grade terms are: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark and Fancy Intense. Fancy Deep is the term used to represent moderate to strong colours that are dark in appearance. Fancy Vivid represents hues that are medium to light but very saturated.

The locations of boundaries between different Fancy grade terms vary depending on the diamond's hue. For example, a relatively rare diamond colour such as blue, which typically occurs in lower saturations, is assigned certain "Fancy" grades at lower saturation levels than a colour such as yellow, which usually occurs in higher saturations.

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