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The 4 C’s
The price of a diamond is determined by four main factors, forming what is called call the 4 C’s: Carat weight, Clarity, Color and Cut.

We highly advise you to look up specialized books or publications before proceeding to evaluate diamonds offered for sale. The following facts about diamonds correspond only to the minimum knowledge you should possess on this subject when choosing a diamond.

Carat weight

The first criterion when deciding a diamond’s value. Weight is always expressed in carats (1ct = 0,20g) and in its subdivisions, the points (1point = 0,01ct). The carat value rises with the weight, because big stones are more rare than smaller ones. For diamonds of the same quality, the cost of two half-carat stones is less than that of a single one-carat piece.

Clarity
Clarity is defined by the absence of inclusions visible with the unaided eye or through 10X magnification. Clarity is defined by different grades represented by letters and numbers:

>F (Flawless) Total absence of inclusions and total absence of minor surface blemishes (with 10X magnification).
>IF (Internally Flawless) Total absence of inclusions and presence of very minor surface blemishes (with 10X magnification).
>VVS1 (Very Very Small inclusions) Presence of minute inclusions difficult to see even for a skilled grader and/or minor surface blemishes (with 10X magnification).
>VVS2 (Very Very Small inclusions) Presence of minute inclusions difficult to see even for a skilled grader and/or minor surface blemishes slightly more present than in VVS1 (with 10X magnification).
>VS1 (Very Small inclusions) Presence of small inclusions clearly visible and/or minor surface blemishes (with 10X magnification).
>VS2 (Very Small inclusions) Presence of small inclusions clearly visible and/or minor surface blemishes slightly more present than in VS1 (with 10X magnification).
>SI1 (Slightly Included) Important presence of small inclusions and/or surface imperfections (with 10X magnification).
>SI2 (Slightly Included) Important presence of small inclusions and/or surface slightly more present than in SI1 (may be seen with the unaided eye by a skilled grader).
>I1 (Imperfect) Obvious presence of inclusions, generally white, and/or important surface imperfections (seen with the unaided eye).
>I2 (Imperfect) Same as I1 with amore obvious presence of inclusions, generally black and/or very important surface imperfections.
>I3 (Imperfect) Very included stone.

Tip: To check the clarity grade in the SI2 and lower grade and to avoid being bothered by reflection, which tends to mask imperfections. Look at the stone with the magnifying lens through the pavilion, table down on a sheet of white paper.

Color

Another factor affecting price. The total absence of color in a diamond is very rare. A totally colorless stone is considered having the highest value. As a general rule, diamonds tend to have a yellow tint, due to the presence of atoms of nitrogen in the structure.

One Exception: pronounced red, blue, pink, green or yellow colors, called “fancy,” are also very rare and claim high prices. Letters in a scale, ranging from colorless to yellow, represents diamond color.

Letters in a scale, ranging from colorless to yellow, represents diamond color. This scale with its different grades is given for your information only. Today, the international diamond trade tends to consider only the GIA (Gemological Institute of America) scale. Its gradation starts with D (colorless) and ends with Z (fancy yellow).

View the GIA scale

Beware

when looking for a diamond’s color use daylight from the North or tube light corrected “daylight”.

When checking a diamond’s color, avoid being bothered by unwanted reflections. These tend to mask the color. The best way is to look at the stone through the girdle, table down on a folded white paper (see sketch).


Cut (or proportions)

In order to preserve the maximum of weight from the rough, the cutter has to make choices that will have a direct effect on the stone’s proportions and their qualities. If the cut diamond has a deep pavilion, the stone will appear less lively or even dark. With a shallow pavilion, it will display a light hole or a fisheye effect at the center due to the absence of internal reflection. A perfectly cut stone should send back the full amount of light through the table without leaks through the back facets.

Many different cutting factors can also affect the beauty and therefore the value of a diamond. A more or less wide table will show respectively more or less fire (or dispersion), the ability of a ray of light to split in rainbow colors. A girdle too thin can easily break during setting. Etc.

The cut is defined by 5 different grades:
Excellent - Very good - Good - Medium - Poor.

Other minor factors affecting the value of a diamond
>Finish
The presence of polishing lines, of a bearded or misaligned girdle, or a table or culet slightly off center, or an imperfect octagonal table, or a bad junction between table and pavilion facets, or missing or extra facets, are factors that belong to the finish grade if they don’t have an effect upon the clarity grade.

Different appreciations used in the finish grade are:
Excellent - Very good - Good - Medium – Poor

>Fluorescence
The property of a diamond, and of other stones, to change or to emit a form/color of luminescence when excited by invisible rays like X rays or ultraviolet rays (UV). While excited by UV light, the emitted color is generally blue. A small amount of stones can show a pink, green, orange or yellow color. Approximately 35 % of diamonds on the market have UV fluorescence. Some diamonds emit a very strong fluorescence when excited by sunrays. This can give them a cloudy or milky appearance. Moreover, this fluorescence, generally blue, tends to mask under sunlight the real color of the diamond (generally yellow or brown) and therefore falsify the color grade.
The appellation “blue-white”, now forbidden for diamond, indicate a stone with a very strong fluorescence masking its true color. In fact “blue white” diamonds can be in reality slightly, and sometimes even strongly, yellow or brown.

Different appreciations of the fluorescence grade are:
Nil (or none) - Slight (or faint) - Medium - Strong - Very strong

Examples
>George, VS1, excellent, good, medium
It means a stone of G color, clarity grade VS1, excellent proportions with a good finish and a medium fluorescence.

> Henry, VVS1, very good, medium, nil (or none)
It means a stone of H color, a clarity grade VVS1, very good proportions with a medium finish and no fluorescence.