Lab-grown diamonds are fascinating gems created using sophisticated technologies that mimic the natural diamond-forming conditions. There are two main methods for producing these diamonds: High-Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD).
High-Pressure High Temperature (HPHT) involves using heavy mechanical presses and intense heat to replicate the conditions under which natural diamonds form deep within the Earth. Chemical Vapor Deposition (CVD), on the other hand, superheats gas into plasma, releasing carbon atoms that build a diamond crystal at the atomic level.
While these methods produce diamonds that are optically, chemically, and physically identical to natural ones, they do result in distinct types of inclusions. Recognizing these inclusions is crucial when grading the clarity of lab-grown diamonds, a key aspect of their value.
Watch How Lab-Grown Diamonds Are Made Using the Chemical Vapor Deposition (CVD) Method
Inclusions in HPHT-Grown Diamonds
The HPHT process uses a metallic catalyst to dissolve carbon, which then migrates to a diamond seed to stimulate growth. Sometimes, pieces of this catalyst get trapped within the diamond crystal, leading to distinctive inclusions.
1. Metallic Features
These are pieces of undissolved flux, often made of iron or nickel, that solidified as the diamond cooled.
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2. Metallic Needles
Common in HPHT diamonds, these inclusions are long and thin, often aligning with the crystal growth pattern.
Image Source: IGI
3. Dendritic Remnants
These branch-like inclusions are relatively rare and can resemble trees or bushes. They form when molten flux becomes trapped by the growing crystal.
Image Source: IGI
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Inclusions in CVD-Grown Diamonds
In the CVD process, carbon atoms rain down on a substrate of diamond seed, growing the diamond in vertical layers. This process also results in unique inclusions.
1. Comet-like Remnants
These carbon inclusions appear comet-like and form when crystal growth continues around dark or opaque inclusions.
Image Source: IGI
2. Planar Clouds
These are groups of small growth remnants that occur on a single geometric plane due to interruptions in the crystal growth process.
Image Source: IGI
3. Internal Graining
Also known as Stria, these reflective lines or angles are caused by stops and starts in the vertical CVD crystal growth.
Image Source: IGI
Common Inclusions in Both Natural and Lab-Grown Diamonds
Certain inclusions can be found in both natural and lab-grown diamonds. These include:
Bruise: A small area of impact with tiny feathers.
Cavity: A large or deep opening in the gemstone.
Chip: A shallow opening in the gemstone.
Cleavage: A crack parallel to one of the diamond’s crystallographic planes.
Cloud: A group of minute growth remnants giving a cloudy appearance.
Feather: A fracture resembling a white feather.
Pinpoint: A tiny dot-like growth remnant.
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Blemishes in Both Natural and Lab-Grown Diamonds
Blemishes are often caused by polishing or wear after sale. They include:
Abrasion: Minute nicks along facet junctions.
Burn Mark: Hazy areas caused by excessive heat or uneven polishing.
Extra Facet: An unnecessary facet placed without regard to symmetry.
Nick: A small notch on a facet junction.
Pit: A small opening resembling a tiny white dot.
Polish Lines: Parallel ridges left by polishing.
Scratch: A thin white line on the gemstone’s surface.
Surface Remnants in Lab-Grown Diamonds
These are similar to Naturals and Indented Naturals found in natural diamonds:
Surface Remnant: Part of the rough stone left unpolished.
Indented Surface Remnant: Part of the rough stone dipping below the polished surface.
Fun Fact: HPHT Magnetism
Some HPHT-grown diamonds contain enough metallic remnants to be picked up with a magnet. Additionally, these diamonds may be falsely identified as moissanite by handheld electronic diamond testers, which measure electrical conductivity.
Understanding these unique characteristics helps in appreciating the beauty and complexity of lab-grown diamonds. For more information on diamond detection and false positives, refer to our post on Diamond Detection and Handheld Testers.