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Treatments There are two types of treatments: treated natural diamonds, and synthetic diamonds. Treated natural diamonds The aim of treating natural diamonds is to artificially improve their quality by changing one or several of their characteristics, thereby increasing their value. Such treatments generally target color and purity. For color, treatments can help to resolve problems related to quantity and uniformity: if a jeweler needs a hundred or so identically colored diamonds to set in a pavé, treating an entire lot of diamonds will enable him to obtain a more uniform color. The main types of treatments are presented hereunder. This list is as complete as possible however this area is still the subject of much research and development. a. Modification of purity Crack filling : process of filling natural cracks or cleavages with substances that have a refractive index similar to that of diamonds. In this way, the light is less refracted than it would be if the cleavage were filled with air - and therefore much less visible. Laboratories do not issue certificates for diamonds that have undergone this type of treatment. Laser drilling : this process aims to lighten or completely eliminate dark inclusions. A tiny canal is laser-drilled and high pressure boiling acid is then injected in the hole. Laser drills are mentioned on certificates. b. Modification of color - Heat treatment or annealing : this technique produces black diamonds. Low quality diamonds are exposed to very high temperatures (around 1000°C) for several hours, until graphite residues appear in the heart of the crystal, making it dark and opaque or even uniformly black. Laboratories do not deliver certificates for these treated diamonds. - Irradiation : exposure of a diamond to a source of radiation will change the position of atoms within the crystal lattice, which will cause its color to change. Green, blue and black diamonds can be created using this technique. Laboratory certificates mention "treated". - Irradiation + heat treatment : after a first transformation via irradiation, the color can be changed again by exposing the diamond to temperatures of around 800°C. This will again re-position atoms within the crystal lattice, and atomic defects can be repaired or removed. The diamond will absorb light differently and will thus take on another color. As a general rule, brown, yellow orange, blue, pink and purple diamonds can be obtained with this treatment. Laboratory certificates mention "treated". - HPHT (high pressure, high temperature) : this process subjects the diamond to a combination of very high pressure (HP) and very high temperature (HT), similar to the conditions in which diamonds are formed in nature. This will cause imperfections in the crystal lattice to be "repaired", provoking a change in its color. Depending on the type of stone that is treated, the HPHT process can make a stone more colorless, or can produce blue, yellow orange, yellow green, pink or brown diamonds. Certificates mention "HPHT". - Coating : with this process, a thin layer of colored substance is deposited on the diamond in order to change its original color. Coating is falling into disuse and laboratories do not issue certificates for these types of treated diamonds. Color Heat treatment Irradiation Irradiation + heat treatment HPHT treatment Blue x x x Green x Yellow orange x x Yellow green x Pink x x Brown x Black x x Synthetic diamonds Synthetic diamonds are created artificially from carbon. This process barely requires three weeks, compared to tens of thousands of years for natural diamonds. Only laboratories possessing leading-edge technology are able to detect these diamonds, which have exactly the same physical and chemical properties as natural diamonds. Laboratories do not deliver certificates for these stones. Two different techniques are currently used to produce synthetic diamonds : - HPHT (high pressure high temperature) : this is the best-known technique. HPHT subjects carbon atoms to very high temperatures and pressures, re-creating the geological conditions in which diamonds crystallize. Diamonds created using this technique are extremely similar to the "real thing" and one of the only ways to detect them is to use special equipment that can reveal the growth lines of the crystal. These lines are younger in synthetic diamonds than in natural diamonds and this can be seen. HPHT processes produce yellow and orange diamonds that can be quite large (0.5 to 3 carats). - CVD (chemical vapor deposition) : this technique was developed in the late 1960's and involves the propulsion of CO2 into plasma. The diamonds created with that process are low nitrogen type IIa crystals. Their color is usually brown, but also sometimes colorless, faint pink, blue or black.