This section contains basics of diamonds and explanation of some advanced topics. We strongly recommend going through this section. There is much more than Four C’s for analysis but they are the most fundamental concepts for analyzing diamonds.

There has been lot of research going on for many years on diamonds. Various universities and gemological laboratories are continuously doing research on diamonds. Analysis of diamonds is basically divided into four C’s. Four C’s are internationally recognized for diamond analysis and grading. The explanation of these four C’s is as follows.

They are:

1. Clarity
2. Color
3. Cut
4. Carat Weight

1) Clarity

The process of the growth of a diamond in the interior of the earth did not occur evenly, but in several phases. In these various phases, the conditions – pressure, temperature and cooling – did not always remain constant and that caused internal features, so called inclusions. These inclusions have the major impact on diamond cost. Clarity features are represented by internal defects inclusions and external defects. The internal defect of a diamond cannot be removed without weight loss.

All other factors being equal, defect -free diamonds are considered the most valuable.

When examining the inclusions, it is important to observe them through crown. Following points should be considered during inclusion examination.

• Size and number of inclusions
• Visibility of inclusions
• Appearance of inclusion
• Nature of inclusions
• Position of inclusions
• Type of inclusion
• Influence on brilliance and durability of stone

The list of internal and external features of a diamond is as follows:

Internal Features

1. Pinpoint
   A very small inclusion, which usually appears as a point under the Loupe. Some specimens contain groups of pinpoints.
    
2. Needle
   A long thin crystal - acicular inclusion.
    
3. Cloud
   Hazy or milky zone consisting of a great number of tiny inclusions.
    
4. Cracks (also called feathers)
   A cleavage fracture or fissure with an irregular path inside the stone, usually breaks the surface of the stone. Types of cracks are as follows.
    
   1. Cleavage Cracks
      These occur in the direction of the cleavage planes parallel to the four octahedral faces. They always occur in straight lines and the cleavage plane often shows a fine striation, similar to that of a cleaved piece of wood.
       
   2. Fracture Cracks
      These can occur in all directions and do not run along a cleavage plane. Their direction is irregular and often jagged. Fracture cracks are caused mainly by mechanical means, such as pressure or a blow.
       
   3. Tension Cracks
      These are caused by differential thermal expansion of an included extraneous crystal and often into the interior from the surface.
       
   4. Feathers
      All types of cracks, which are perpendicular to the crack plane and appear white and feathery are termed “feathers” or “glets”. Also small blow marks and indentation marks on the edge of a facet are sometimes so described.
       
5. Nick
   A small and shallow pit typically occurring on the girdle edge. Some nicks may have a greater size.
    
6. Cavity
   A large three-dimensional opening on the surface of a polished diamond.
    
7. Bearded girdle ("bearding")
   Micro cracks extending from the girdle into the stone.
    
8. Bruise
   A deformation zone on the diamond surface caused by a blow.
    
9. Crystal in crystal
   A diamond microcrystal inclusion in polished diamond.
    
10. Knot
    A diamond inclusion standing out against the surface of the polished.

External Features

1. Abrasion
   Smoothing of edges and vertexes mainly caused by careless cutting. Micro cracks orientated along the edges are often perceived as white lines rather than sharp edges.
    
2. Extra facet
   A facet present in addition to those required by a given cutting style and which does not fit the symmetry pattern.
    
3. Natural
   Part of the original natural diamond surface which is left on the polished stone after cutting.
    
4. Pit
   Micro opening which often appears as a white point.
    
5. Polish lines
   Thin parallel lines left after polishing; thin parallel ridges within one facet caused by the irregularity of the crystal structure; small parallel polished trenches formed by the cutting disk surface.
    
6. Polishing marks
   Hazy areas of the stone surface caused by excess heating (superheating) during cutting or polishing.
    
7. Rough girdle
   Feathery or cavernous girdle surface, often with micro cracks.
    
8. Scratch
   A linear trench, which typically appears as a thin white line (curved or straight).
    
9. Surface graining
   Defects and distortions of the diamond crystal structure which reach the surface of the stone and often cross facet junctions.

Clarity Grading

Clarity of the diamond is divided into following grades

FL (Flawless): no blemishes or inclusions when examined by a skilled grader under 10X magnification.

IF (Internally Flawless): no inclusions when examined by a skilled grader, and only insignificant blemishes under 10X.

VVS1 & VVS2 (Very Very Slightly Included): Minute inclusions that are difficult to see. In VVS1, they are extremely difficult to see, visible only from pavilion, or small and shallow enough to be removed easily by repolishing. In VVS2, inclusions are still very difficult to see. Typical inclusions: scattered pinpoints, faint clouds, slightly bearded girdles, internal graining, and tiny feathers, chips, and bruises.

VS1 & VS2 (Very Small Inclusions): Minor inclusions ranging from difficult to somewhat easy to see. Typical inclusions: small included crystals and feathers, distinct clouds, and groups of pinpoints.

SI1, SI2 & SI3 (Small Inclusions): Noticeable inclusions that are easy (S1I) or very easy (S2I) to see. Inclusions are often centrally located and noticed immediately; that may be eye -visible. Typical Inclusions: included crystals, clouds, and feathers.

I1, I2 & I3 (Imperfect): Obvious inclusions that are often easily eye-visible faceup; in I3, they may threaten durability. Typical inclusions: large included crystals and feathers.

2) Color

The color of the diamond is very important factor in determining the value of the stone. The colorless diamonds are costliest. The grading of the color is carried out with the help of master stones. The diamond to be graded is compared to a master stone to determine its exact color. There are very minor variations in color shades, which is very difficult to differentiate with untrained eye. A letter denotes a diamond grade. The colorless diamond is assigned D and it is increased up to Z as the intensity of the color is increased. Due to perception ability of human's eye, even two stones of the same color can be perceived in a different way. Hence, to ensure the correctness of the color grading, a diamond should be examined on both sides of a masterstone.

3) Cut

The cut of the diamond is one of the few things, which are in human’s hand in making a polished diamond. Cut is very important factor in diamond pricing because it is directly related to diamond’s beauty. Brilliance and firing of the diamond is directly related to its cut. The cut quality is a complex parameter, which can be defined as a combination of Proportions, symmetry, and polish:

Cut grading = proportions grading + symmetry grading + polish grading

A stone shows the maximum brilliance and fire only when it’s cutting proportions exactly correspond to those calculated from physical and optical laws.

When analyzing the cutting of the diamond, following points should be taken into consideration.

• Table size evaluation
• Crown angle evaluation
• Examination of pavilion facet reflections
• Girdle Evaluation
• Estimation of pavilion depth
• Estimation of culet size
• Effect of proportions on stone value

Following is the list of main parameters of a cut diamond.

• Average girdle diameter (mm) (the mean value of the minimum and maximum Diameter) is taken as 100%;
   
• Table size (% of the average girdle diameter);
   
• Total depth (mm and % of the average girdle diameter);
   
• Crown height (from the upper edge of girdle to table; % of the average girdle
  Diameter);
   
• Pavilion depth (from the lower edge of girdle to culet; % of the average girdle Diameter);
   
• Girdle thickness (qualitative grading or % of the average girdle diameter);
   
• Crown angle (degrees; the angle between the bezel facets and the girdle Plane);
   
• Pavilion angle (degrees; the angle between the pavilion main facets and the Girdle plane);
   
• Culet size (qualitative grading).

The quality of polishing is also considered in diamond cut evaluation because the polish of diamond contributes to its firing and brilliance.

5) Carat Weight

Diamond weight is measured in carats. A carat is a unit of weight. Carat weight is one of the most important factors in deciding price of the stone. The weight of the diamond is taken into consideration first when analyzing the diamond. Carat is most commonly abbreviated as “ct”. The weight of a diamond is generally indicated to the second decimal point. For example if the weight of a diamond is one and quarter that means 1.25 ct.

1 carat = 0.2 gram= 100 points