About Light

Light, wavelengths and color, and everything we perceive through our eyes, are intricately related.

There are many different wavelengths around, ranging from 400 nanometers to 800 nanometers. And each wavelength gives us a perception of a different color.

Of all these different wavelengths/colors, there are three primary colors and each of these primary colors has one secondary color:

Primary and Secondary colors cancel each other out: a blue wavelength accompanied by a yellow wavelength of the same intensity will give us the perception of seeing white.

Combinations of primary and secondary colors

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However if the blue wavelength is unaccompanied by its yellow counterpart, then we will have the perception of seeing blue.

What would make the color "Yellow" disappear? Absorption by objects: when light hits an object, the object will, depending on its composition, absorb some of the wavelengths and in varying degrees. If all the light that hits the object manages to escape, then we see white; and if none of the light manages to get out, then we see black.

So basically what we perceive as the color of an object is actually the part of the light that escaped from the object: by playing around with all the wavelengths and all the different degrees of absorption for each of them, we see the infinite variety of colors around us.

About Diamonds

An absolutely perfectly pure, "white" diamond would be composed of carbon atoms arranged in a perfect tetrahedral lattice. With this atomic structure, none of the light would be absorbed, the diamond would return all the light it receives and would be perceived as completely colorless.

However such diamonds don't exist: during their crystallization phase, diamonds lie 150 to 200 km under the earth's crust, and are subjected to pressures of about 70,000 kg/cm2 (about 1,000,000 pounds/in2) and to temperatures ranging from 1300 to 2000°C. (2300 to 3600°F). Under these conditions, diamonds lose their atomic integrity: their orderly tetrahedral structure is twisted and they come to absorb other types of atoms. As a result, they do not reflect all the light they receive - some of the wavelengths are absorbed and the diamond takes on some color.

Diamonds are classified depending on what happened to them during their crystallization phase.

Type I Diamonds

Are diamonds that ended up absorbing a detectable quantity of nitrogen atoms, which absorb blue light.

Type Ia: If the nitrogen atoms are clustered together within the carbon lattice, then the diamond is said to be a Type Ia diamond. Because these diamonds absorb blue light, they can have a pale yellow color. 98% of diamonds are Type Ia

Type Ib: If the nitrogen atoms are evenly spread out throughout the carbon lattice, then the diamond is said to be a Type Ib diamond. These diamonds absorb green light as well as blue light, and have a darker color than type Ia diamonds. Depending on the precise concentration and spread of the nitrogen atoms, these diamonds can appear deep yellow ("canary"), orange, brown or greenish. Less then 0.1% of diamonds belong to Type Ib.

Type II Diamonds

Are diamonds that absorbed no, or very few, nitrogen atoms.

Type IIa: These diamonds can be considered as the "purest of the pure" - they contain no, or minuscule amounts of impurities and are usually colorless. Unless, that is, the carbon tetrahedrons that make up the diamond were twisted and bent out of shape while the diamond rose to the surface of the earth. An imperfect carbon lattice will make the diamond absorb some light, which will give it a yellow, brown or even pink or red color. 1-2% of diamonds belong to Type IIa.

Type IIb: These diamonds contain no nitrogen - but they contain boron, which absorbs red, orange and yellow light. These diamonds therefore usually appear to be blue, although they can also be grey or nearly colorless. All naturally blue diamonds belong to Type IIb, which makes up 0.1% of all diamonds.

Summary of diamond classification

What about green diamonds?

Green diamonds are a separate case: these diamonds can contain clustered nitrogen atoms or they can contain no nitrogen atoms - what gives them their color is that they have been bombarded by nuclear rays during their growth. This bombardment makes them absorb magenta wavelengths, which gives them their green color. These diamonds are extremely rare.