A diamond is estimated according to the 4 C : cut, carat, clarity, colour.

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1. The cut

Diamond Cut refers to the quality of a diamond’s proportions, angles, symmetrical facets, fire, brilliance, scintillation and finishing details. It determines the beauty of the diamond. It's the most important criterion. It can be observed to the naked eye. The diamond must be cutted and polished according to well-defined proportions. The diamonds have a high dispersion of the light. This dispersion is the cause of the flashes of colours, what we call the fire of the diamond. A diamond well cutted seemes full of flashes of colours.

The grades of the cut are :
- Ideal,
- Excellent, 
- Very Good, 
- Good, 
- Fair,
- Poor.

The cut is determined too by the parts of the diamond : the table, the crown, the girdle, the pavilion and the culet.

The Ideal and Excellent grades signify proportions and angles cut for maximum brilliance and fire.
One special Ideal cut is the "hearts and arrows". Under a special light, we can see 8 hearts and 8 arrows perfectly symmetrical. This cut is rare due to the time to cut it and the waste of rough diamond.

 

2. Carat - weight

1 carat = 0.20 g.

This unit has nothing to do with gold carats. 

An idea of what represent carats in diameter :

- 0.03 carat = 2 mm

- 0.05 carat = 2.5 mm

- 0.07 carat = 2.7 mm

- 0.10 carat = 3 mm

- 0.15 carat = 3.40 mm

- 0.20 carat = 3.80 mm

- 0.25 carat = 4.10 mm

- 0.33 carat = 4.40 mm

- 0.40 carat = 4.80 mm

- 0.50 carat = 5.20 mm

- 0.65 carat = 5.60 mm

- 0,75 carat = 5.90 mm

- 0,85 carat = 6.20 mm

- 1,00 carat = 6.50 mm

- 1,25 carat = 7.00 mm

- 1,50 carat = 7.40 mm

- 1,75 carat = 7.80 mm

- 2,00 carats = 8.20 mm

- 2,25 carats = 8.60 mm

- 2,50 carats = 9.00 mm

 

3. Clarity

The clarity of a diamond is defined by its blemishes and its inclusions. Too much inclusions and blemishes prevent the light from dispersing. So the diamond has less flashes of colour.
The clarity is analysed by an expert with a magnifying glass 10 x or with a binocular microscope.

- FL (Flawless)
- IF (Internally Flawless)
- VVS1 (Very, Very Slightly Included 1)
- VVS2 (Very, Very Slightly Included 2)
- VS1 (Very Slightly Included 1)
- VS2 (Very Slightly Included 2)
- SI1 (Slightly Included 1)
- SI2 (Slightly Included 2)
- I1 (Inclusions 1)
- I2 (Inclusions 2)

The inclusions are dissolved with laser or acid and filled with resin but they are noted anyway in the clarity.

 

4. Colour

There are a lot of coloured diamonds. The colour analyses white diamonds. More colorless they are, more flashes of colour they disperse.

- Colorless : D - E - F : D diamonds are rare.
- Near colorless : G - H - I - J : they contain traces of colour. 
- Faint color : K - L - M : color (usually a yellow tint) is more easily detected by the naked eye.
- Very light color : N to R : yellow or brown tint.
- Light color : S to Z :  for many people, they have too much color for a white diamond.