Fancy Colored Diamonds

Colored Diamonds

Diamond (from the ancient Greek αδάμας – adámas "unbreakable") is a meta-stable allotrope of carbon, in which the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding  between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material.  

Diamonds have remarkable optical characteristics. Since diamonds have an extremely rigid lattice they can be contaminated by very few types of impurities, such as boron and nitrogen. Combined with wide transparency, this results in the clear, which contributes to the colorless appearance of most natural diamonds.

Small amounts of defects and/or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green (radiation exposure), purple, pink, orange or red. Diamond are the most popular gemstone because they have a relatively high optical dispersion. Optical dispersion refers to the ability to disperse light of different colors, which results in their luster characteristic. The combination of optical dispersion/luster and the diamond’s natural hardness makes it the most sought after gemstone.

Diamonds have a wide band gap of 5.5 eV corresponding to the deep ultraviolet wavelength of 225 nanometers. This means pure diamonds should transmit visible light and appear as if is a clear colorless crystal.

Colors in diamonds originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations. Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by high-pressure high-temperature techniques, have been detected in diamond as individual atoms; the maximum concentration is 0.01% for Ni and even much less for Co. Virtually any element can be introduced to diamond by ion implantation.

Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds.

Boron is responsible for the blue color in diamonds. Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds; and plastic deformation of the diamond crystal lattice. Plastic deformation is the cause of color in some brown, pink, and red diamonds.

 

Below is a list of fancy colored diamonds in order or rarity:

Yellow Diamonds

Brown Diamonds

Colorless Diamonds

Blue Diamonds

Green Diamonds

Pink Diamonds

Orange Diamonds

Purple Diamonds

Red Diamonds.

Black Diamonds

 

Black Diamonds or “carbonado diamonds” are not truly black, but actually contain numerous dark inclusions that give the gem their dark appearance.

Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless.

Most diamond impurities are carbon flaws, which replace a carbon atom in the crystal lattice.  The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present in the stone. The GIA classifies low saturation of yellow and brown diamonds as diamonds in the normal color range and apply the traditional diamond color grading scale. This scale grades the color of the diamonds from “D” (colorless) to “Z” (light yellow). Diamonds of different colors, such as blue diamonds are called fancy colored diamonds and fall under a different grading scale.

Yellow or brown color diamonds having color more intense than "Z", as well as diamonds exhibiting color other than yellow or brown are considered fancy colored diamonds. These diamonds are graded using separate systems, which indicate the characteristics of the color and not just its presence.

These color grading systems are more similar to those used for other colored gemstones, such as: rubies, sapphires, or emeralds rather than the traditional white diamond color grading scale.  Any light shade of diamond other than light yellow or light brown automatically falls out of the traditional white diamond scale. For example, a pale blue diamond won't get a "K", "N", or "S" color grade, it will get a Faint Blue, very Light Blue, or Light Blue grade. Laboratories use a list of 27 color hues that span the full spectrum for colored gems and diamonds.

 Red, Orangish-Red, Reddish-Orange, orange, Yellowish-Orange, Yellow-Orange, Orange-Yellow, Orangish-Yellow, Yellow, Greenish-Yellow, Green-Yellow, Yellow-Green, Yellowish-Green, Green, Bluish-Green, Blue-Green, Green-Blue, Greenish-Blue, Blue, Violetish-Blue, Bluish-Violet, Violet, Purple, Reddish-Purple, Red-Purple, Purple-Red, Purplish-Red

A modifying color combination can also be added (e.g., Olive or Brown-Olive) for stones without the purest hues. Additionally, for diamonds the following colors are used: White (which are milky), Black (which are opaque), Gray, Pink, Brown. The saturation of these hues is then described with one of nine descriptors: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark, Fancy Intense, Fancy Deep, Fancy Vivid.

The terms 'Champagne', 'Cognac' and 'Coffee' refer to different types of brown diamonds. In the diamond processing/dealing industry, the word 'Brown' is considered a killer as far as diamond value goes. Even though champagne is a light yellow color, champagne diamonds are Light Brown. Cognac is usually used to describe a diamond that is Orangish-Brown because cognac is a deep golden-orange color. Coffee is usually used to describe a diamond that is a Deep Brown or Vivid Brown color. Some grading agencies may also describe brown stones as Fancy Yellowish-Brown, Fancy Light Brown, Fancy Intense Brown, etc.

Diamonds that enter the GIA’s scale are valued according to their clarity and color. For example, a "D" or "E" rated diamond (both grades are considered colorless) is much more valuable than an "R" or "Y" rated diamond (light yellow or brown). This is due to two effects: high-color diamonds are rarer, limiting supply; and the bright white appearance of high-color diamonds is more desired by consumers, increasing demand. 

 

Fancy diamonds are valued using different criteria than those used for regular diamonds. When the color is rare, the more intensely colored a diamond is, the more valuable it becomes. Another factor that affects the value of Fancy-Colored diamonds is fashion trends. For example, pink diamonds became more valuable because of the demand on them after Jennifer Lopez (J-LO) received a pink diamond engagement ring. Le Vian has taken this same angle by marketing dark brown diamonds “Chocolate Diamonds.” Deep-colored fancy colored diamonds, such as the hope diamond have become the most valuable diamonds in the world, due to how rare they are.

Synthetic colored diamonds

 

The majority of synthetic diamonds are yellow in color and are produced by High Pressure High Temperature (HPHT) processes. The yellow color is caused by the nitrogen impurities. Other colored diamonds may also be reproduced such as blue diamonds, green diamonds, and pink diamonds. These fancy-colored diamonds are reproduced by adding boron or from irradiation after synthesis.

Another popular method of growing synthetic diamond is chemical vapor deposition (CVD).  The growth occurs under low pressure (below atmospheric pressure) and involves feeding a mixture of gases (typically methane to hydrogen) into a chamber and splitting them to chemically active radicals. This method is generally used for coatings, but can also produce single crystals several millimeters in size.

As of 2010, nearly all 5,000 million carats of synthetic diamonds produced per year are for industrial use. Around 50% of the 133 million carats of natural diamonds mined per year end up in industrial use.The cost of mining a natural colorless diamond runs about $40 to $60 per carat, and the cost to produce a synthetic, gem-quality colorless diamond is about $2,500 per carat.However, a purchaser is more likely to encounter a synthetic diamonds when looking for fancy-colored diamonds. Nearly all synthetic diamonds are fancy-colored, while only 0.01% of mined natural diamonds are naturally colored diamonds.

Diamond enhancements are specific treatments performed on natural or synthetic diamonds, which are designed to better the gemological characteristics of the stone in one or more ways. The diamond enhancements are generally performed on diamonds that are already cut and polished into a gem. Some of these diamond enhancements include:

laser drilling to remove inclusions from the diamonds

application of sealants to fill cracks in the diamonds

treatments to improve a white diamond's color grade

treatments to give fancy color to a white diamond