Natural Fancy Black Diamond
Natural Fancy Black Diamond
Diamond made opaque by graphite, hematite, or fracture-network inclusions, distinct from treated black goods
A natural fancy black diamond is a diamond whose body appears black to the unaided eye because dense dark inclusions or networks of fractures absorb and scatter light through the body of the stone. The cause of colour is mechanical and inclusion-driven rather than electronic in the lattice: graphite, magnetite, hematite, ilmenite, and pyrite inclusions, often present in quantities of tens of thousands of microscopic particles per stone, render the diamond effectively opaque. Fancy black diamonds occupy a separate market position from the more familiar coloured fancy diamonds (yellow, blue, pink, green) and are graded on the GIA fancy-colour scale with explicit notation of cause of colour.
Cause of colour
Three mechanisms produce the black appearance. The first and most common is dense graphite inclusions: clusters of graphitic carbon throughout the diamond absorb visible light and produce the metallic-grey to black appearance, often with a characteristic surface lustre when the diamond is polished. The second is heavy iron-oxide and sulphide inclusions — magnetite, hematite, pyrite — which produce a similar opaque appearance but sometimes with a more brownish or reddish cast. The third is dense networks of internal fractures that scatter light without absorbing it; stones in this category may show a slightly lighter, almost translucent black under transmitted light.
Most natural fancy black diamonds combine more than one mechanism. The combination of graphite inclusions and dense fracture networks is particularly common in the alluvial diamonds of the Central African Republic and parts of West Africa.
Distinction from carbonado
Natural fancy black diamond is distinct from carbonado, the polycrystalline black diamond aggregate found principally in alluvial deposits in Brazil and the Central African Republic. Carbonado is a sintered aggregate of microscopic diamond crystals with intergranular porosity, generally not transparent or translucent at any scale, and used historically as industrial cutting and polishing material rather than as a fancy gem. The visual distinction is in lustre and structure: a carbonado has a characteristic pebbled, dull-to-greasy surface, while a natural fancy black diamond cut into faceted form shows a more metallic surface lustre.
Distinction from treated black diamond
The other distinction that matters for trade purposes is between natural and treated black diamonds. Most black diamonds in commercial jewellery are not naturally black but have been treated to produce the colour, principally by high-pressure-high-temperature graphitisation of internal fractures (HPHT) or by neutron or electron irradiation that produces dense colour-centre absorption. Treated black diamonds are typically cheaper than natural fancy black, often by an order of magnitude, and are routinely used in mass-market black-diamond jewellery. Disclosure of treatment is required under the FTC Jewelry Guides and equivalent regulation in other jurisdictions; sale of treated black diamond as natural is misbranding.
Laboratory testing distinguishes natural from treated black diamonds by the pattern and distribution of inclusions and fractures, by characteristic spectroscopic signatures of irradiation or HPHT, and by the geometry of the colour distribution within the stone. GIA grades natural fancy black diamonds and notes the cause of colour explicitly on its reports.
Cutting and care
Black diamonds are cut differently from transparent diamonds. The cutting goal is surface lustre rather than internal brilliance: a fancy black diamond's optical effect comes from light reflected off the polished facets, not from refraction through the body. Step cuts (emerald, baguette) and brilliant-style cuts both work, but the depth and proportion calculus is different from transparent stones, since light return from the pavilion is not the design objective.
The fracture networks that contribute to the black colour also make the diamond more brittle than transparent diamond. Cutters approach black diamond rough with extra care for chipping, and finished stones should be set in protected mounts (bezel, half-bezel, or recessed prong) where the girdle and pavilion are protected from impact. Standard hardness (10 on Mohs) applies to the diamond material itself, but the inclusion-rich body has reduced toughness compared with cleaner stone.
The market
Market interest in natural fancy black diamonds increased substantially in the late 1990s and 2000s, driven by contemporary high-jewellery designs from de Grisogono, Solange Azagury-Partridge, and several other houses that built collections around the unusual visual character of the stones. Prices for natural fancy black diamonds remain modest compared with other fancy colours — typically a small fraction of fancy yellow or fancy brown per carat at equivalent weights — reflecting both the inclusion-rich character of the material and the more limited consumer demand. Treated black diamonds dominate the mass-market segment and trade at substantially lower prices again.
Famous examples include the Black Orlov (a 67.50-carat cushion-cut stone of disputed natural origin) and the Spirit of de Grisogono (a 312.24-carat black diamond carved into the largest cut diamond known in any colour for several years after its 2002 completion).