Learn more about diamonds: Diamond's colour and diamond's fluorescence

The diamond is translucid or transparent.
The light breaking index of diamond is particularly high and depends on the lenght of the wave: these characteristics give the diamond its characteristic sparkle, « adamantin ».

1- The colorless diamond

The most frequently found color of diamonds is white : actually free from color. 
In this case it is the colorless or almost colorless diamond that is the most sought after.
The diamonds reflect the light and break it into a rainbow of colors. This small reflection of color, or flash, has no effect on the technical evaluation of the color.²
Rare diamonds without a trace of color are graded D. This grade can vary from D to Z depending on the intensity of color, starting from absolutely free of color to light yellow, brown or grey.
The color of a diamond is affected by chemical impurities and/or structural defects in the atomic structure of the carbon crystal.

D   exceptionally white +
E   exceptionally white
F   extra white +
G   extra white
H   white
I/J  white with slight trace of color
K/L slight hue
M-Z hue

The grading of the diamond’s color can only be executed on a single, unmounted stone.
To determine the exact hue present in uncolored diamonds, a certified comparison diamond is used, which is presented by the GIA. The stones are examined in special white lighting. The stones used for comparision are chosen with the help of numerous criteria.

The majority of uncolored diamonds will glow when exposed by ultraviolet light: this phenomenon is called fluorescence. It is not directly linked to the color of a diamond, it shows the amount of absorption of UV light.
The degree of fluorescence is defined by it’s intensity:
- no fluorescence
- faint
- medium
- strong
- very strong

The fluorescence is seen as an impurity and therefore will have a negative effect on the value of a diamond. Diamonds with no fluorescence are very rare.

In very highly graded colors like D, E and F, fluorescence has a slight effect on the transparency of the diamond. Ironically, for stones in the lower color categories like I, J and further down, the blue-ish fluorescence can rule out a bit of the yellow mostly seen in these diamonds, and therefore has a positive effect on the diamond’s value.
While the fluorescence can have an effect on the certification of a diamond, while buying one this effect is rarely of influence on choosing the stone. But it plays a big role for de value of a diamond.

Private Diamond Club only presents diamonds with no or faint fluoresence.

2- Colored or « fancy » diamonds

While a faint yellow hue (ranging from I to Z) can lower the value of a diamond, naturally colored stones can reach very high prices. The diamonds exists in all colors, of whih red is the most rare. Because the diamonds are colored (and not slightly tinted) they are not classified by letter but by the name of the color and it’s intensity.

These rare colored diamonds are referred to as fantasy (or fancy) and are graded with the help of a group of different color characteristics, for example the hue and the saturation.

Colored diamonds are the most expensive because they are extremely rare. The most sought after are the most intense and heavily colored stones.

In this table the different hues and saturation in the color yellow are shown, these tables exist for every color (blue, pink, red etc.). The basic color of the diamonds can be graded by these characteristics. For example, a diamond is graded as Fancy Yellow, or Fancy Vivid Yellow.