What is a CVD stone (lab-grown diamond)? Difference between CVD and HPHT

Lab-grown diamond is a pure carbon crystal that is chemically, physically and optically identical to a natural diamond. The only difference is that it does not take millions of years deep underground; It occurs within a few weeks under controlled laboratory conditions.

Therefore, a lab diamond is not an 'imitation' or 'fake' stone. Stones such as zircon (cubic zirconia) or moissanite are different materials that resemble diamonds; Lab diamond is the real diamond itself. Its hardness is 10 on the Mohs scale, and its refractive index and shine are the same as natural diamonds.

Lab diamonds, just like natural stones, are graded and certified by independent laboratories such as GIA or IGI according to 4C (cut, color, clarity, carat) criteria.

CVD is the abbreviation of the English words 'Chemical Vapor Deposition'. In this method, a thin plate of diamond 'core' (seed) is placed in a vacuum chamber. The chamber is filled with carbon-containing gases such as methane.

At high temperature (approximately 800–1200 °C), the gas breaks down into plasma and the released carbon atoms collapse layer by layer on the seed crystal, enlarging the diamond. The process takes place at relatively low pressure.

Stones produced by CVD generally grow with uniform layers; Brown tones may occur in some stones during production, which can be removed by post-growth treatment.

HPHT stands for 'High Pressure High Temperature' and imitates the conditions in which natural diamonds are formed on earth. The carbon source is melted under a temperature of approximately 1300–1600 °C and very high pressure of 5–6 GPa (gigapascals).

In these conditions, the carbon dissolved in the molten metal catalyst crystallizes on a seed crystal and forms diamond. The HPHT method is also used to improve the color of other manufactured or natural stones.

The main difference is the production environment: HPHT uses high pressure + high temperature and imitates natural formation; CVD, on the other hand, grows layer by layer from the gas phase at low pressure.

The crystal shape is also different: HPHT stones grow cuboctahedral (multidirectional), while CVD stones grow in a single direction, layered. This difference is used by expert gemologists to distinguish the origin of the stone.

For the daily user, the result does not matter: a correctly cut CVD stone with high color and clarity cannot be distinguished from a HPHT stone of the same quality with the naked eye. Both have the same hardness and shine; The selection is usually made based on the stone's individual 4C quality and price.