The value of a polished diamond is mainly determined by four factors (the so called four C’s):
- Carat weight;
- Clarity; and
The first three are reflections of how perfectly a diamond was formed, while the fourth, cut, is added during the polishing process.
The factors that generally determine the value of a diamond:
- The larger (heavier) the diamond, the more expensive it is;
- The whiter (more colourless) the diamond the higher the value;
- Superior clarity (fewer inclusions) increases the value;
- The closer the polishing is to an ideal set of standards, the higher the value.
Large, colourless, inclusion free diamonds with an ideal cut (polish) are a rare find; therefore, they have the highest value.
This principle excludes the fancy colour diamonds where the rarity of the colour is the main factor determining the value.
The grading of diamonds may appear to be puzzling as there are a few grading systems that are used to grade diamonds. The GIA (Gemological Institute of America) grading system is regarded as the standard of reference on which most grading institutions base their grading.
The GIA Grading System:
A. GIA Colour Grades
Colour grades are allocated using the letters of the alphabet, starting with D through to Z:
Grades D to H: Colourless (white) with D the highest colour grade.
Grades I to L: Progressively more tinting of the diamonds. I represents the least and L the most obvious tinting.
Grades M to Z: Obviously coloured with increasing intensity of the colour.
Note: Stones with a colour more intense than “Z” are grades as Fancy Colour Diamonds.
Colour Grading method:
A diamond is graded by comparing it with a set of master colour reference stones. Colour grading instruments can also be used.
Yellow and sometimes brown, are the most common tints seen in diamonds.
2. GIA Clarity Grades:
Virtually all diamonds have inclusions consisting of mineral crystals, growth artefacts, cracks, fractures and so forth. The only inclusion free diamonds are the two top grades Flawless (FL) and Internally Flawless (IF).
Clarity Grading Method - Clarity grading is done under a 10x magnification as the standard reference procedure.
The following grading scale is used:
- Top grade clarity with no inclusions or surface marks.
IF (internally flawless)–
- No inclusions but have surface marks, e.g. polish marks.
VVS (very, very small inclusions) –
- Very difficult to see inclusions under magnification.
- Divided into VVS1 (the higher grade of the two) and VVS2.
VS (very small inclusions) –
- Very small inclusions which are somewhat difficult to find under the 10x magnification.
- Divided into VS1 (the highest clarity grade of the two) and VS2.
SI (slightly included/ small inclusions) –
- Small inclusions but noticeable under a 10x magnification.
- Divided into clarity grades 1 and 2 with SI1 the higher clarity grade.
- Some grading systems also add and additional grade, SI3.
- Depending on the position and its darkness the inclusions may be visible with the unaided eye from grade SI2 and lower.
I (Included) or P in some reports –
- Obvious inclusions, visible without magnification (unaided eye)
- I1 – obviously included, but the quality of the stone is not significantly impaired.
- I2 – More heavily included, and some surface reaching fractures can be observed, which impairs the quality.
- I3 – This is the lowest clarity grade; with quality and durability seriously impaired.
The visibility of an inclusion is sometimes more obvious in a diamond, due to:
- The position of the inclusion (inclusions in centre are more obvious);
- Its colour, darker inclusions are more readily recognised; and
- The cut of the diamond. Inclusions are more readily visible in some fancy cut stones.
(SSW/ Aug 2017) Next Article: Potential pitfalls with grading.