Advanced Diamond Info

An in-depth look at some other characteristics of diamonds: fluorescence, type I and II diamonds, and fancy colours.

Type I Diamonds

In the 1930's it was discovered that about 98%-99% of all found diamonds contained nitrogen (N) as their primary impurity. This nitrogen is detected using a spectroscope, as the nitrogen absorbs infrared light. This impurity usually occurs in one of two ways, either in large groups (aggregates), of nitrogen, or as single nitrogen atoms scattered within the diamond's crystal lattice. These two forms of impurity are further broken down into two sub-groups: Type Ia and Ib.

Type Ia diamonds are those diamonds that contain nitrogen in aggregates. When these aggregates occur in pairs within the diamond lattice (A aggregates) or as aggregates of four (4) nitrogen atoms (B aggregates) they do not absorb any of the wavelengths of visible light. When nitrogen occurs in groupings of three (known as N3 center) however, the nitrogen groups absorb the visible light within the blue end of the spectrum, causing a yellowish colour to appear in the diamond. This means that the nitrogen in Type IaA-aggregate and IaB-aggregate diamonds does not affect a diamond's colour, whereas the nitrogen of Type IaN3 center does affect the diamond's colour, saturating it with the yellowish tint we are familiar with.

Type Ib diamonds are far less common than Ia, occurring in less than .1% of all naturally occurring diamonds. Type Ib diamonds are diamonds that contain single nitrogen atoms scattered throughout the diamond's crystal lattice framework. It is this scattering of single nitrogen atoms, allowing the absorption of visible light in the blue end of the spectrum that gives rise to the intense yellow colour found in the true Canary yellow diamonds (rare and valuable Fancy coloured diamonds). This atomic formation can also give rise to browns and yellowish -green diamonds.

Type II Diamonds

In Type II diamonds, there is no sign of nitrogen present when viewing the diamond's light properties on infrared light with a spectroscope, as there is little absorption of infrared light occurring within these diamonds. This does not mean that absolutely no nitrogen atoms are present within the diamond's crystal lattice. The spectroscope's resultant findings simply indicate that nitrogen does not appear in a large enough quantity to have any affect on the diamond's optical properties. Type II diamonds are also split into two categories, Type IIa and Type IIb. These sub-groups are separated with Type IIa diamonds not capable of conducting electricity and Type IIb diamonds that are able to conduct electricity.

Type IIa diamonds are colourless, unless they have an inclusion or defect in the crystalline structure that would allow light absorption to occur. Diamonds of this type can be gray- brown, yellow, pink, light blue, or light green (with these two last arising from radiation exposure), but more often these are the perfectly colourless diamonds that most people are looking for. This is due to the fact that their structure does not easily absorb short-wave ultraviolet light wavelengths, but instead allows the light to pass through. Such famous diamonds as the Cullinan (the world's largest cut diamond, found in the South African Premier Mine in 1905) and the Koh-i-Noor (Urdu for "Mountain of Light"), which was found in India and now rests in the Tower of London, are type IIa diamonds.

Type IIb are diamonds that are electrically conductive, and the most distinguishing feature is the presence of boron (B) in this type. Boron is not present in Type IIa diamonds, and serves as the primary difference between the sub-groups. The presence of boron within this diamond type causes almost all of them to be either blue or bluish gray. Boron, as a foreign element in Type IIb diamonds, provides the blue colour due to the boron's absorption of light towards the red end of light's colour spectrum.

The colour of "fancy" diamonds comes from the mineral elements found in the individual diamond, such as chromium, magnesium, cobalt, titanium, iron, vanadium, nickel and copper. The pink colour of some diamonds, as well as the rare green, often get their colour not from trace elements, as with the other coloured diamonds, but from radiation and temperatures acting during the diamond's formation. "Fancy" diamonds are some of the best known and famous. One of the most famous diamonds, the dark grayish-blue, 45.52 carat Hope Diamond, is also one of the most sought after, and costly, of all diamonds.

All fancy colour grading must be made under a prescribed set of conditions. These conditions include: viewing the diamonds under a 10x loupe by three trained gemologist; viewing the diamond in a diamond box (which provides a white background and white surroundings); viewing the diamond through the table, pavilion down; and viewing the diamond from multiple angles, still with the pavilion down.

The GIA Fancy Coloured Grading Scale

GIA does not grade fancy coloured diamonds on the colourless diamond colour-grading scale. They instead use a scale that rates the diamond's colour on three primary characteristics: Hue, Tone and Saturation.

Hue: The Hue in colour grading refers to the primary and notable colours that are present in the diamond, such as Pink, Blue, Yellow, Brownish-Yellow, and so on. GIA recognizes 27 hues in grading fancy coloured diamonds.

Tone: The Tone of colour grading refers to the lightness or darkness of the hue, or primary colour of the diamond.

Saturation: Saturation is the measure of how strong and intense the primary colour of the diamond actually is, such as light, deep, intense or vivid.

The 9-grade GIA colour grading scale runs as follows:

• Faint
• Very Light
• Light
• Fancy Light
• Fancy
• Fancy Dark
• Fancy Deep
• Fancy Intense
• Fancy Vivid

This grading scale measures how the level of colour saturation is found in a given fancy coloured diamond. It is also important to note that when a fancy coloured diamond is being graded it is viewed from the top down, as opposed to the normal grading method for colourless diamonds (which are looked at with the bottom, or pavilion up and the top, or table, down).

In recent years fancy coloured diamonds have gone from being interesting oddities and curio pieces to being immensely sought after and greatly desired gems in their own right. Many of the world's most famous diamonds (such as the South African mined 128.54 carat, canary-yellow Tiffany diamond, brought out in 1877) have been fancy coloured diamonds. This mixture of history and celebrity has only increased the current desire for fancy colour diamonds.

The very colour of fancy coloured diamonds also makes them more difficult to cut properly. Fancy coloured diamonds have their own demands for the diamond cutter, in that the diamond cutter is not cutting to produce the same effect that is sought after in colourless diamonds. In the case of fancy coloured diamonds, the main goal of the diamond cutter is to preserve and enhance as much of the natural colour of the diamond as is possible. Therefore, it is to this end that the cutter must strive to facet and polish the diamond to facilitate the entering light to produce the most vivid display of the diamond's colour. In the end, the goal in cutting a fancy coloured diamond is not to produce maximum scintillation or fire, although these are desired, but to bring out the most colour. The very nature of the fancy coloured diamonds preclude them from being particularly exceptional in brilliance and fire, as many wavelengths of the entering light are being absorbed by the diamond's colour producing agent, whether this be foreign matter, irregular crystal growth or radiation.