India being a major cutting and polishing center as well as exporting country for diamonds, it is absolutely necessary to educate the Indian industry about the qualitative aspects of the diamonds.

In the international markets there exists various standards for grading of diamonds; the most important being CIBJO (European standard) and GIA (American standard).

In India, there is no any specific standard for diamond grading and hence most of the exporters grade and classify diamonds according to their convenience.

Grading and classification of diamonds are based on the internal features and defects seen in diamond. Grading of diamonds according to the commercial point of view, began in the beginning of the last century in Paris. About 100 years back Paris was the most import and trade center for diamonds. In order to differentiate the clean diamonds from those diamonds having inclusions, two designations were arrived at, "pure" for clean and "pique" for spotted diamonds.

In course of time, the term "clarity" was preferred to "pure" as purity suggests that there are only two types of diamonds, pure and impure.

Diamond grading is based on the qualitative aspects such as clarity, colour, cut and carat weight - popularly known as 4-C's. These fundamentals have been defined according to various classifications. Two of the major standards emerged in the world today are GIA (Gemmological Institute of America) in the United States of America for American standards and CIBJO (International Confederation of Jewelry, Silverware, Diamonds, Pearls and Stones) for European standards.

Out of the above four quality factors, this articles will be dealing with the clarity grading aspects of diamonds. The clarity or purity of a polished diamond depends up on the inclusions, cracks, cleavage, or other natural fractures or external defects present in a diamond. Another words inclusions are the basic parameters on which the clarity grading is done.

The colour of inclusion is equally important aspect. It should be noted very carefully as to what is the colour, w3hether it is black or colourless or any other colour. Many a time, a single inclusion may appear more prominent than a collection of several smaller colourless inclusions. Similarly a colourless transparent mineral inclusion is less obvious than a coloured inclusion of the same size. Some of the coloured inclusions can be seen with naked eye. These inclusions may also hamper the brilliance of a diamond. Some of the inclusions are crystalline. The shape of the inclusions is also important. Some are flat, some are pin point.

Inclusions are also in the form of cracks and sometimes thes4e cracks may dev4elop further. Due to external mechanical stress like that can happen while setting or while removing the diamonds from its setting, sudden temperature changes etc. can enlarge a fracture or a cleavage and tension cracks. Therefore larger cracks are generally evaluat4ed at a lower scale than solid crystalline inclusions which cannot change any further. In other words, it is not only the size of the inclusions is important, its nature is more important. Cracks which are exposed to the surface of the stone contain sometimes a coloured liquid, which makes them more obvious and diminish the brilliance of the diamond. This is the nature of the inclusions and should be studied carefully.

Equally important or perhaps the most important is the position of inclusions in diamond. There could be a lot of difference in the grades of diamonds having identical inclusions, one on the girdle and another under the table. In other words, two identical inclusions could lead to two different grades. Types of cracks, perpendicular to the cleavage plane and appear white and feathery are graded differently, because of their positions in the diamond.

Diamond having reflection inclusions near the facet edges are assigned lower grade as they are more clearly visible than similar inclusions which are not reflected.

Magnification :

It is an internationally accepted trade practice to use ten times of magnification with an achromatic and aplanatic loupe for clarity grading.

Illumination :

The lighting is very important. Diffused light should be ideal for determination of the inclusions. Day-light lamps used for colour grading is a suitable instrument. Soft light causes strong surface reflections and viewing inside would be more difficult and hence such soft light should be avoided.

Diamonds do not have fluid inclusions. The inclusions in diamonds are generally crystalline solid inclusions of minerals, not like inclusions, clouds, cracks (cleavage, fracture, tension cracks.) etc. and which are wholly or partly surrounded by the stone.

Cleavage cracks occur in the direction of the cleavage planes which are parallel to the four octahedral faces. Cleavage planes often show fine striations. Along the girdle of the diamond may a time fine hairline like cracks are developed due to the carelessness and fast bruiting, of the rough diamond.

Fracture cracks are irregular and often jagged and can occur in any direction. These cracks do not run along a cleavage plane. Fracture cracks are caused by some mechanical reasons like pressure of a blow. Both cleavage and fracture cracks can occur in the stone internally or can penetrate deeper in to the stone from the surface.

Tension cracks are caused by differential thermal expansion of an included crystal of a foreign mineral and often surrounded the inclusion in a fan like manner.

Feathers are caused due to a small blow or an indentation mark on the edge of the facet.

Crystalline inclusions are included minerals which according to their nature can be colourless, reddish, brown, yellowish greenish or black.

Structural phenomena are mostly clouds or obscurities consisting of microscopically small crystals of dust like appearance or they look like clouds in the sky. When these clouds are small in quantity and spread out, the impact on the clarity of the diamond is much low. If they are large and compact, they do infuence the transparency and the brilliance of a diamond and hence the diamond is to be down graded.

A twinning plane is the growth plane between two thin crystals. In this plane the twin crystals meet in mirror image. This is generally a straight line, but many a times it appears as curved when viewed through the opposite side of the stones. Thus twinning lines which occur in the pavilion are seen through the crown appear definitely curved because of the cone shape of the pavilion.

Many a time the twinning lines of twin crystals show a slight yellow or brown coloration which makes them appear as thin reflecting areas inside the stone, which is classified as twinning planes.

In any case, these twinning planes / lines influence the clarity grade of diamond.

Twinning lines are evaluated as external faults when graded for the cut.

Growth lines and planes are in-homogeneties which originated during the growth of the diamond. Growth planes are such irregularities which occur internally and which influence the clarity grade.

LOUPE CLEAN (IC)

A diamond can only be termed loupe clean if an expert examines it with a ten times achromatic and aplanatic loupe in normal light and it is found to be absolutely transparent and free from inclusions nothing is seen. It is Loupe Clean.

Further external features or faults include fractures, extra facets, dot-like inclusions, blow indentation, natural crystal faces (naturals) scratches, polishing marks, polishing traces, damaged edges, burnt facets and other surface defects.

American and Scandinavian countries consider the internal and external defects in their clarity grading. That is the reason the scale of the American and Scandinavian nomenclature begins with the term "flawless". This term refers to cut diamonds, which are free from internal and external faults, the term fla3wless defined by GIA states that cut diamonds are termed as flawless if no internal or external defects can be seen under a ten times magnification. However smallest external faults as extra facets or naturals, which are not larger than the widest part of a fine girdle and which do not in any way influence the symmetry of the girdle nor are visible through the crown are not characterized as external defects.

Internally flawless (IF) is defined by GIA as diamond is considered to be internally flawless if it is free from internal false under ten times magnification. Certain external faultless such as small polishing marks which can be removed with a minimum loss of weight, extra facets and naturals also above the girdle are excluded.

These definitions mean, that a diamond which is described as loupe clean in Europe could in America or Scandinavia be classified as VVS, VS or even SI because of external defects. But in the final evaluation, both systems evaluate the stone at the same level; what one system grades under clarity, the other deals with under cut grading.

These terms describe cut diamonds which when viewed through a ten times achromatic and aplanatic loupe by an expert show only very, very small inclusions which are very difficult to see.

Crack like inclusions which are separately recognizable fringes on the girdle, as well as small blow indentations which may extend into the interior of the stones are counted into this clarity grade. The inclusions should be light coloured.

The term comprises cut diamonds which, when viewed with ten times magnification, have small inclusions. These are usually easily to be been with a 10x loupe and at the same time not seen with the naked eye through the crown side. The inclusions under the table should be light, they should not be too obvious, around the girdle there can be small dark inclusions.

Lately this grade is not sub-divided any more, that is, the group has been condensed and inclusions which up to some time ago would be classified as SI1 and SI2, are now graded as I1.

The SI2 grade has inclusions that can be easily seen with 10x loupe in the table but not visible with naked eye. It may have some definite external features.

With increasing size and number of inclusions in the I grades two further definite criteria are added. : recognition with the naked eye, solely through the crown in natural day light and the influence of inclusions on the brilliance effect.

This t6erm comprises cut diamonds, which when viewed with ten times magnification show several Inclusions immediately, but which do not impair the brilliancy. With the naked eye, when viewed through the crown, these faults even in larger stones are only discernable with difficulty. Typical defects of this group are larger colored inclusions as well as larger cracks or plane - like clouds. It is also termed as I1

This lowest grade of clarity comprises cut diamonds with large and / or numerous which are very easily visible through the crown with the naked eye, and these inclusions diminish the brilliancy of the diamond considerably. The group has definite external faults. It is also grouped as I3.

Some grades of clarity grouped according to number, position and size of inclusions are given below as sketches. Table (crown) and pavilion facets are marked with inclusions. Red markings indicate internal inclusions and green marking indicated external blemishes. These markings are guidelines and not exact inclusions.

Verena Pagel - Thaisen "Diamond Grading ABC".

Eric Bruton "Diamond".

GIA "Diamond Symposium".

CIBJO "Diamond Book".

G.I.I. "Diamond Grading" notes.