In other articles in this series we looked at the various ways in which modern, technological processes can be used to improve the perceived quality of a diamond – laser drilling and fracture filling. In this article we shall be taking a closer look at a number of processes that influence and enhance the color of a diamond.
Natural, fancy colored diamonds are a rarity, in fact, only one out of every 10,000 diamonds possess natural coloring and can be classified as a “fancy colored diamond”. So, unlike white or clear diamonds where the less color means a greater value, with natural fancy colored diamonds the intensity and distribution of color within the diamonds matrix increases its value. As a result, over the years at least three techniques have been developed that enhance or even alter a diamonds natural color.
Note: As with any diamond that has been treated to improve the natural characteristics and qualities it displays after cutting and polishing, color enhanced diamonds should not be considered natural fancy colored diamonds and their price should reflect this.
Diamond were being given a coat of tinfoil on their pavilion (back) surfaces as far back as the early 1700’s. Early plated diamonds were often set closed back settings so that identifying the coating was problematical. However, because of the relatively primitive techniques used, the coating was prone to flaking or the accumulation of moisture between the coating and the diamond. Strangely, because of their antique value, coated diamonds from this era (and the Victorian period) does not, usually, detract from the value of older jewelry.
Over the years, moderntechnology has introduced new, difficult to detect coating techniques such as the use of violet to blue dyes and vacuum coating processes. Dye processes can often be revealed and removed by soaking the diamond in hot water or wiping with alcohol making them prone to damage during day to day usage.
Note: Reputable diamond dealers and stores will tell you if a diamond has been given a coating to alter its color. If they don’t and you find out the diamond has been coated, you could have grounds for pressing charges of fraud against the seller. If in doubt – ask!
The first attempts at using radiation to enhance a diamonds color was made by Sir William Groakes in 1904. Diamonds that he immersed in radioactive radium salt turned a dark green. This process had a number of drawbacks: the color was not uniform, it only effected the diamond’s surface, and it left the diamond highly radioactive. So much so, that the diamond, which is held by the British Museum, is still unwearable due to its radiation levels.
Note: If the last paragraph has you worried – then don’t! The irradiation and annealing treatments in use today have come a long way from those early experiments are 100% safe!
Four different techniques are in common usage today. All work by altering the diamond’s crystal matrix, displacing carbon atoms which produces localized concentrations of color. All irradiated diamonds produce diamonds with a green, black or blue hue. However, additional heat treatments (annealing) can produce yellow, orange, pink or brown diamonds.
Without going into scientific details and explanations, they are:
Cyclotrons are used to bombard diamonds with protons and deuterons. After treatment with the cyclotron, diamonds has a bluish to green surface color. After heating this can change to orange or yellow.
Diamonds are exposed to concentrated and focused cobalt-60 gamma rays. This process produces a blue colored diamond but, as it can take several months to complete, is less commonly used today.
Diamonds are exposed to and saturated with neutrons which give them a blue to black color that permeates the entire stone. If heated to temperatures of up to 900 °C can change the color pink, orange, yellow or brown.
Diamonds are treated to an electron bombardment from Van de Graff generators and take on a blue to green color that only penetrates about 1 mm. into the diamond. Heating up to 1200 °C can result in pink, orange, yellow or brown diamonds.
This is a relatively new process first used by General Electric in 1999. By subjecting diamonds to pressures of up to 70,000 atmospheres and temperatures of up to 2,000 °C (3,630 °F) used this process to transform brown, type IIa diamonds to colorless or almost colorless stones (some may have a slightly pink hue).
Note: The HPHT process is very similar to the process, introduced by the General Swedish Electric Company in 1952) and General Electric in 1953 for the production of synthetic diamonds.
Later it was discovered that the same process could be used to transform type IIb brown diamonds into blue diamonds and type IaA and IaAB diamonds to yellow-orange and yellow-green.
The HPHT process is a much more expensive one than irradiation treatments but it does have the advantage of producing colored diamonds where the color is considered to be permanent and stable even under extreme conditions (heat). As a result, this technique has gained great popularity since its introduction.
Note: HPHT treated diamonds can only be identified by fully equipped gemological laboratories with the equipment needed for a full spectroscopic examination and professional staff able to interpret the results of testing. Diamond Certificates from reputable gemological labs will show if the diamond has been irradiates or undergone any other color enhancement process.
In conclusion, buying a diamond or a piece of diamond jewelry usually marks a significant event in your life (and a lot of money). You have the right to get full value for your investment and total disclosure regarding any enhancement techniques used on the diamonds you’re buying. Ask to see the gemological certificate and also ask the seller if the diamond has been treated and how? This way, you’ll be able to know if you’re getting a fair deal.
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