Colour grades

For each coloured stone variety, a set of colour grades and qualities are determined. The colour grade ruler allows one to evaluate the quality of the gem. In most cases, rare colours would fetch higher gem values. The rarer the colour, the greater the demand for it, generally resulting in a higher worth of the gem as buyers would be willing to pay more for it. Colours corresponding to more than one gem type are graded differently for every case, using separate colour grading rulers (or sets of rulers) and pricing lists.

Following is the colour scale, which is in use by most of the professional trade members, and will be used in the course. For the sake of the visualization of each colour grade, a tanzanite colour ruler, made up of actual gem images and Gemewizard colour references, was chosen to demonstrate the topic.

GEM   The gemstone displays the most attractive and sought-after colour (which is usually also the rarest one). GEM-grade stones usually produce a vividly-saturated, medium-toned colour.

AAA   The gemstone displays a good colour, very close to the GEM quality. AAA-grade stones usually produce a highly saturated, medium-light or medium-dark toned colour.

AA   The gem displays a relatively good colour. This grade also acts as the separating border between high quality goods to medium ones. AA-grade stones usually produce a moderately saturated colour, with a light or dark tone.

A   The gem displays a nice pleasant colour, but of medium quality. A-grade stones usually produce a slightly pale colour, with a very gentle touch of grey or brown.

B   The gem displays a low quality colour. B-grade stones usually produce a pale and/or dark colour, with a nuance of grey or brown.

C   The gem displays the lowest quality of colour seen in gem materials. C-grade stones usually produce a very pale and/or very dark colour, with a noticeable greyish or brownish tint.

Some traders use other grades in their grading scale. These grades are usually part of their own in-house grading method. Even if some of these grade names are used by other traders, they are inconsistent in their meaning. Such grades may include:

• High grades of 4, 5 or even 7 times A ('AAAAAAA'). These grades sometimes replace the GEM grade.
• New highest grade of 'Super Gem' (representing a stone with a high quality above the regular GEM grade).
• A specific grade called 'Gem Dark' for over toned, good colour gems.
• A sub grade between A and AA called A+

As these grades are inconsistent and not widely accepted, for the purpose of this course, we shall not use them.