Growth Principle
HPHT Rough Diamonds: Using the high temperature and high pressure method, simulating the formation conditions of natural diamonds in the earth's mantle, carbon atoms are placed in growth chambers, and through high temperature (about 1,500 degrees Celsius) and high pressure (about 60,000 atmospheres), the carbon atoms crystallize on the diamond crystal seeds to form diamonds.
CVD Rough Diamond: Using the chemical vapor deposition method, carbon containing gases (such as methane) are mixed with hydrogen in a high temperature and low pressure reaction chamber, and heated by microwave plasma, hot wire, laser or arc discharge to dissociate the carbon atoms in the gas and deposit them layer by layer on the substrate to form diamond crystals.
Color
HPHT Rough Diamonds: The primary colors are usually D - E, less often F, with a few blue tints.
CVD Rough Diamonds: Primary colors are predominantly F, with fewer D - E colors, and a few shades of brown or green, but a variety of colors can be obtained through post-processing.
Clarity
HPHT Rough Diamonds: Due to the presence of metal mediators during the growth process, high clarity diamonds are produced in relatively small quantities, and some diamonds may be magnetic.
CVD Rough Diamonds: grown in a relatively pure environment with few impurities, usually of high clarity, no metal inclusions, non-magnetic.
Size
HPHT Rough Diamonds: Due to technical limitations, diamonds of less than 2 carats are produced, with fewer diamonds above 3 carats.
CVD rough diamonds: more suitable for the production of large carat diamonds, mainly concentrated in more than 1 carat, more than 2 carats of the process has obvious advantages.
Internal Characteristics
HPHT Rough Diamonds: Often contain metal inclusions such as iron, nickel and cobalt, which are used in the growth process and sometimes enter the diamond crystals as part of the identification of the diamond as a laboratory-grown diamond.
CVD Rough Diamonds: Usually contain no metal inclusions, but may have graphite or other mineral inclusions as a result of the growth process.
Growth Form
HPHT Rough Diamonds: occur as cubes or octahedrons that may develop into rhombic dodecahedrons or other complex crystal forms with 14 growth directions.
CVD Rough Diamonds: Usually cubic in shape with only 1 growth direction.
Cost and Price
HPHT Rough Diamonds: The production process requires specialized high temperature and high pressure equipment, which is costly to produce, has higher operating costs, and produces a relatively low yield, making it slightly more expensive than CVD Rough Diamonds for the same parameters.
CVD drills: The production process is relatively simple, the cost is low, and it has a certain cost advantage in mass production, so the price is relatively more affordable.
