Fashion for black diamonds has reached its peak. Right after the jewelry house Chopard (that has been using black diamonds for a long time), Angelina Jolie and Brad Pitt created cufflinks made of white gold and black diamonds for London-based Asprey.
Jeweler Itay Malkin has designed a ring adorned with a large-sized black diamond dedicated to the Sex and the City 2 movie, where it is of importance.
Gresso company is promoting the Luxor Las Vegas Jackpot cell phone decorated withblack diamonds totally weighing 45.5 carats, while 208 polished black diamonds amounting to 1.34 carats are used to make every Meridiist Black Diamond phone.
Choron Diamond, an Indo-Yakutian joint venture and an official sponsor of the Russian Football Championship, crafted the Choron Diamond Cup in the form of a life-size ball made out of 2.5 kg of gold, grade 585, and 33 140 white and 10 728 black diamonds (indemnified to the tune of $1 million).
Natural color black diamonds are produced by a number of companies, for example, by OOO Rony Carob in Moscow.
However, there is no such a great quantity of genuine black diamonds that circulates on the world market. Most of them are artificially blackened natural gems that initially were of yellow or brown hues.
Three main techniques are used for artificial blackening:
1. Impact graphitization using ultra-short thermal actions, for example, laser exposure. There are two types: a) treatment by visible or infra red laser ranges resulting in multiple inclusions of sub-micron graphite crystals and nano-particles of non-diamond carbon uniformly distributed over the diamond parent matrix; b) exposure to ultra-violet (excimer) laser results in graphitization of the surface layer of about 1 micrometer. Great progress in the study of laser treatment applied to diamonds is achieved in Taiwan (Institute of Electro-Optical Engineering), Switzerland (Gemtechlab), Germany (AphroDiamante GmbH) and France (Institut des Matériaux Jean Rouxel, Nantes). Technological lasers are available in great variety. In jewelry, yttrium aluminum garnet-based neodymium lasers are widely known. These are also used for processing jewelry metals (for example, in welding chain links) and in diamond cutting. To blacken a diamond, a skilled process engineer just needs to select a mode by changing focus, radiation power and dose.
2. Hard neutron radiation creating a bulk structure of radiation damage, mainly vacancy defects (able to join in clusters, nano-cavities or nano-honeycombs of graphite-like structure) in the parent crystalline diamond body. A typical dose is 1017 neutrons per square centimeter. Theoretically, any of the 283 research nuclear reactors existing in the world can be used for diamond blackening operations. Russia ranks first as for the number of research reactors (62), followed by the USA (54), Japan (18), France (15), Germany (14) and China (13). Many small and developing countries also have research reactors, including Bangladesh, Algeria, Columbia, Jamaica, Ghana, Libya, Thailand and Vietnam. De Beers calls on gemmologists and consumers to be careful with such gems due to danger of secondary radiation.
3. Ion bombardment. Subsurface blackening can be achieved by accelerating the ions under vacuum conditions with an implantation energy in a range of between 50-100 keV, for example, by boron or nitrogen ions, with the ion density of 1017 ions/sq.cm. US Patent 7604846 belongs to the Korea Atomic Energy Research Institute. Similar work has been done in Taiwan at the National Tsing-Hua University. The essence of the method lies in the ion implantation into the diamond subsurface layer inducing amorphous phase, which is converted into graphitic phase after annealing. Ion-vacuum processes are widely used in the South-East Asia at many factories producing electronic components (chips, data carriers, etc.). Even written off equipment used in the electronic industry can be adapted for ion treatment of rough and polished diamonds.
According to scientists, gemmologists and business men, from 2008 to 2010, production and sales of blackened diamonds reached a commercial scale. However, real manufactures cannot be identified from open information sources. In particular, it is due to the fact that in a number of countries, some treatment methods are restricted or prohibited. While neutron irradiation is not legal in the U.S., it is used to treat black diamonds for color in other countries.
Only dealers and suppliers of black diamond jewelry declare themselves openly. Most of the suppliers are located in Asia, for example, in India (Global Impex, Khanna Jewels, Bello Jewels, Gemstone, Harsh International, Diajewels), Thailand (Bangkok Gem Mart Co., Metamorphose, Regent Jewellery, Tina Jewelry), Indonesia (Tatra Jasa), China (Apith). There are suppliers in other countries, for example, in Israel (Fancy Diamond Leibish Polnaauer, Just Jewelry), Canada (Global Weather Trade), and Columbia (JGH Import Export).
In Russia, blackening of diamonds is not carried out on commercial scale due to strict government control. This is mainly done abroad, that is why the major channels are loose diamond dealers bringing them from abroad and jewelers making such items abroad and bringing them to Russia.
However, sometimes natural black diamonds can be found on the Russian market. Their color is attributed to the micro-inclusions (in particular, those of magnetite causing weak magnetism which can be good for health, whereas, the properties of irradiated polished diamonds are hazardous to health).
Experienced gemologists, like those from the Moscow State University Gemmological Center, can easily distinguish between the natural black color by non-carbon inclusions; in this respect, inclusions of magnetite, enstatite, olivine, polydymite, chalcopyrite, native iron, earlier thought as a defect, now are considered to be a positive criterion being an evidence of natural color. “Radiation” black diamonds can be easily identified due to several features well studied in the radiation materials technology, for example, by radiation crystal swelling.
However, there are no reliable techniques to identify natural and artificial graphitization and unfair jewelers so far make use of the situation.
Vladimir Teslenko, for Rough and Polished
