CVD vs. HPHT: Breaking Down the Differences

CVD – Chemical Vapour Deposition

  • Process used to create gem-grade diamonds as well as optics and semiconductors
  • Uses ultra-pure carbon-rich gasses in a controlled chamber where they are heated until they break apart, allowing the carbon atoms within the gas to separate, and finally, fall onto a diamond substrate layer by layer, resulting in a rough diamond crystal
  • Process takes between six to ten weeks and yields gem-grade Type IIa diamonds
  • Modified versions of CVD which produce different chemical reactions:
    1) Low-pressure CVD (LP-CVD)
    2) Microwave Plasma Vapor Deposition (MP-CVD)
    3) Ultrahigh Vacuum CVD (UHV-CVD)
    4) Plasma-enhanced CVD (PE-CVD)


HPHT – High-Pressure High Temperature

  • Recreates a diamond's natural growing environment found deep within the Earth
  • Has the ability to build up the pressure of almost 60,000 atmospheres and temperature of 2,500 degrees Celsius
  • The catalysts inside the HPHT chamber are the first to react to the added heat and pressure and change from solid to molten form causing the graphite to dissolve
  • The cooling process takes several days, allowing the carbon atoms to build upon the original diamond seed
  • Three primary tools necessary for the production of lab-grown diamonds:
    1) Bars Press: uses combination of inner and over anvils to apply hydraulic pressure to the diamond seed/growth cell
    2) Belt Press: capable of producing several diamonds in one cycle by using two large anvils that press together to create the necessary pressure
    3) Cubic Press: Uses six separate anvils to create necessary pressure for diamond crystal growth, and also used to create diamond powder for industrial purposes

Both laboratory methods are capable of producing high-quality grown diamonds, but they still differ in popularity. Even though scientists have always advocated for the HPHT method since it imitates the same environment as a diamond from the Earth and is typically the faster process, CVD has become the method of choice for those selling larger bridal stones. Whether they’re made by CVD or HPHT, “lab-grown diamonds have the same exceptional hardness, stiffness, and thermal conductivity as their Earth-mined counterparts”. The GIA (Gemological Institute of America) even grades them according to the same 4Cs—cut, clarity, color, and carat—that gemologists use to assess diamonds formed in the Earth.

Source: VIPortal