Black diamond engagement ring
Types of Black Diamonds
Black diamonds are actually relatively rare in the colored diamond series. Although black diamonds may appear as opaque black blocks, they come in different types:
1、 Natural black diamond
1. Inclusion Color Monocrystalline Black Diamond
Any type of diamond (Type I/II) may have a black appearance due to the presence of a large amount of opaque dark inclusions. The most common and common type of dark inclusion is graphite, which is because diamonds and graphite have the same composition, presenting different mineral phases only due to their different structures. Due to the changes in HP conditions in the deep environment where diamonds are located, local graphitization or the inclusion of a large amount of graphite phase inclusions appear naturally. If diamonds come from deeper sources, they can encapsulate iron mineral components (such as magnetite) during the growth process, giving the diamond an opaque black appearance.
The key identification feature of a single crystal black diamond containing dark inclusions is the dense point like, sheet-like, and irregular mineral inclusions observed at the thin edge thickness through strong light transmission and magnification
2. Monocrystalline diamonds of other dark colors
Diamonds with certain dark levels of color will appear almost black in appearance, such as very deep and dark purple, brown, red, green, and blue. When extremely strong fiber optic lamps transmit through thin edges, their true body color can be seen. The color source identification of this black diamond is the same as its relatively light and bright one
3. Aggregated Black Diamond
Black diamond, composed of a large number of fine-grained diamonds and appearing in aggregate form, is highly valued in industry due to its hardness similar to that of single crystal diamonds, as well as the highest toughness caused by fine-grained aggregates. There are also a small number of faceted gemstones cut and ground with aggregated black diamonds in the current market. The significant difference between this faceted gemstone finished product and the black diamond colored by the package is that the crystal gaps of the aggregate are usually dense and not deep cracks, while single crystals have feather like patterns like ordinary diamonds.
2、 Manual processing of black diamonds
Black diamonds can be obtained through manual processing. Common methods for processing black diamonds include the following:
1. Heat treatment
Heat low-quality single crystal diamonds with well-developed cracks under low pressure conditions. Due to their relatively weak structure, graphitization usually occurs preferentially at these cracks compared to areas without developed cracks. When the number of graphitized cracks is large and they are densely distributed in the diamond, this is common in many industrial grade diamonds and also in many P3 grade diamonds. This way, the heat-treated diamond can present a relatively uniform black appearance. However, due to the feather like and linear cracks in the diamond, the heat-treated black diamond can be observed to have a linear distribution of black under comprehensive illumination (usually fiber optic lamp+overhead lighting).
Although it is currently rare to see, it must be acknowledged that some gray white and gray aggregate diamonds that are not black enough can also have a uniform black appearance through heat treatment. The heat treatment of this type of microcrystalline diamond aggregate not only involves the graphitization of cracks, but also the surface or overall graphitization of some microcrystalline diamonds. Due to the small particle size of the aggregate diamond, this partial diamond microcrystalline graphitization can give the entire aggregate diamond a uniform black appearance. This heat treatment of the aggregate black diamond loses the microscopic characteristics of the natural aggregate black diamond "salt+black pepper powder" and the strong graphite peak in Raman spectroscopy as its key identification points.
2. Irradiation treatment
By irradiating ordinary diamonds, dark green and blue colors with low brightness can be obtained. The appearance of these irradiated dark green and dark blue diamonds is also black. The strong light transmission at the thin edge is green and blue, and the high intensity GR1 peak and the significantly narrow half width at half maximum of the GR1 peak are evidence of their color change by artificial irradiation treatment.
3. Film coating treatment
Covering ordinary diamonds with an opaque black film can result in a uniform black appearance. This treatment is unstable and prone to film abrasion, local detachment, etc., which can be easily magnified and visible under reflected light illumination conditions.
4. Dyeing treatment
Low quality single crystal diamonds with multiple cracks and aggregated diamonds with multiple pores can be easily dyed black. This treatment is also unstable and may cause fading. In addition, the cracks and pores that are dyed the same as other varieties of gemstones have obvious color aggregation and are easy to identify.
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