Today most searched diamond topic is whether the lab grown diamond is CVD or HPHT so let’s understand both the process their advantages and uses in detail.

Diamonds are naturally formed deep inside the earth’s crust and transported to surface by kimberlites and lamporites and finally mined by humans, traded legitimately or illegally, transported to manufacturing companies worldwide to cut and polish assorted and graded for size and quality, certified by labs and sold to customers.

Now the scientists sitting in their research labs created various methods to grow the same diamonds from same raw materials in their crucibles and ovens, trying to perfect mother nature’s creations, altering the speed, colour and size of growth and get it cut and polished assorted and graded for size and quality, and sold to customers.

The most used process of production among dozens of diamond growing methods

1. High Pressure High Temperature (HPHT)

2. Chemical Vapor Deposition (CVD)

 Hpht is a method of growing diamonds very similar to mother nature’s method, the graphite powder along with certain additives are loaded in an anvil of a giant hydraulic press, (fig 1) high pressure and high temperature is applied for few hours and boom diamonds are formed in different sizes and different qualities.

Cvd is a method of growing diamonds where a carbon source for example methane gas is heated in plasma chamber where the methane is turned into plasma and seeds crystals of diamond are placed on a platinum plate where the carbon from plasma cools down and pours like rain droplets on seed crystals and grown layer by layer forming a single diamond crystal of a very controlled and predictable colour, size and quality.

A simple comparision for easy identification and analysis.

HPHT	CVD
Mixed clarity and various inclusion	Generally cleaner and inclusion free
Mixed colour shades due to impurities	Colour can be controlled and optimized
Sizes vary and unpredictable	Sizes are determined by the seed and duration
Crystals grow very similar to natural diamond	Layered cubes with poly crystalline overgrowth
Common colours like yellow or brown	Colourless, pink, blue, and many more
Small and medium sizes only possible	Large crystals over 75 cts are grown already
Mostly abbrasives and gems are made	Gem and scientific research specimens are made
Cheaper to produce large quantites	Expensive to produce
Faster production cycle	Long production cycle
High phosphorescence	Low phosphorescence
Different trace elements are found	Hydrogen is found in lattice
Weaker  fluorescence comparitvely	Stronger fluorescence
Nitrogen related centers in lattice	Nitrogen vacancy centers in lattice
Irregular growth structure can be observed	Uniform growth structure
More consistent spacing in lattice	Slight distorted spacing in lattice
Metallic inclusions can be observed	Polycrystalline diamond can be as inclusion
Black spots, Iron, nickel n cobalt inclusion,	Micro gas bubbles, carbon defects,
	Planar inclusions, striation patterns
Raman spectroscopy 1332 peak,NV peaks	2800-3100, D band 1350,
IR Spectroscopy 3100 small peaks,H defects	1100-1400, CH bands 2950
PL Spectroscopy NV center 575-637 nm,N3center	Variable PL intensity
LIBS stable to temp, consistent composition	High level of hydrogen n gaseous impurities
Cross Polars Microscopy growth pattern	Layered and spectral colours pattern

The above data is compiled to test and certify manmade diamonds and also classify its method of production using highly advanced instruments at our laboratory.

Sandeep Kumar N

Gemologists