The rarity and allure of fancy color diamonds has led the jewelry industry to transform typical “white”, “D”-“Z” scale diamonds into more unique, yet affordable, colorful versions of their pricier, naturally occurring counterparts. Fancy color diamonds are rarer than white diamonds and are sought after for their vivid color and graded differently than rare, colorless diamonds. Some methods of changing the color of a diamond are permanent, while other treatments will fade over time.
Coating diamonds is the most prevalent treatment because of its low cost and beautiful end result.
A very thin silica film is placed over the bottom half of the diamond, the pavilion, which then disperses color through reflection. The material is only 60 nanometers thick (approximately a millionth of an inch) and does not affect overall weight.
Once a coated diamond is set, it is fairly durable, difficult to detect, and protected from most surface scratches. Only mild jewelry cleaner should be used for general care and coated diamonds should not be exposed to excessive amounts of heat, steam, or hot ultrasonic cleaning.
You should always notify your jewelry of any treatments to your stone before taking it in for any repair of cleaning.
Over time, the coating will eventually wear away with normal cleaning and use.
Chemist, physicist, and gem connoisseur, Sir William Crookes, first discovered radiation's effects on diamond color in 1904 he conducted a sequence of experiments using radium salts. Diamonds submerged in radium salt gradually turned the exterior dark green in patches and left the diamonds exceedingly radioactive and unwearable. In 1914, Crookes donated one of these diamonds to the British Museum where it has lost neither color nor radioactivity. Irradiation can also occur naturally, but is rarer.
Today, diamonds are safely irradiated. Irradiation physically alter the diamond's crystal lattice, moving carbon atoms out of place and creating color centers. After the initial irradiation treatment, they turn brown and yellow diamonds into shades of green, blue, or black. Annealing (high heat treatment) is performed to further transform their color into vivid shades of pink, purple, red, yellow, orange, or brown. The annealing process individual carbon atoms more ductile, allowing some of the lattice defects created during irradiation to be adjusted. The final color is reliant on the temperature, length of annealing, and the diamond's composition.
After a diamond had been irradiated, the color is typically permanent, but could perhaps change if high heat is used during repairs.
High Pressure High Temperature (HPHT)
In 1999, General Electric introduced HPHT treatment to specific brown and yellowish diamonds. The end result significantly removes color altogether or enhances the existing color to a more vivid and sought after color. HPHT uses temperatures of up to 2,000 °C (3,632 °F) and pressures of up to 70,000 atmospheres during treatment. HPHT alters the color of nitrogen impurities and also repairs structural deformations that occur during the crystal’s growth.
There are a few companies out there that claim HPHT is simply a technique that completes that job that Mother Nature started versus unnatural treatment while the Federal Trade Commission requires that a stone treated by HPHT be disclosed. Some synthetic diamonds also receive HPHT treatment to alter their appearance and make them harder to differentiate between naturally occurring diamonds.
Gemological Institute of America (GIA) certificates now specify when High Pressure High Temperature treatments are detected by indicating "Artificially Irradiated" or "HPHT Annealed" on the report.
HPHT is permanent and the most difficult treatment to detect.