There's a lot of science and research involved in growing diamonds; we’ll do our best to explain what we’ve learned. So without getting into the manufacturer's science and procedures (because that is all patented and proprietary information), here’s what we know about the science behind creating lab-grown diamonds.
There are two types of processes used when growing a lab-created diamond. HPHT and CVD start with a carbon seed and use different methods to develop a diamond from that seed.
CVD is short for Chemical Vapor Deposition. This means that a material is deposited from a gas onto a substrate (surface or material on or from which an organism lives or grows), and chemical reactions are involved which causes the Diamond to begin to grow. Growth is a very long process; on larger areas (less than 100cm2), diamond is usually deposited at growth rates between 0.1 and 10 microns per hour. To put that into perspective, the average piece of hair on your head is around 45 microns. So it's a very slow process and requires precisely controlled environments and gas levels to form a gem-quality diamond.
HPHT is short for High-Pressure High Temperature. This process has a much more used history in the jewelry industry. Some larger companies started using this process in the 1940-the 50s to make diamonds but were never used or able to make gem-quality diamonds. HPHT uses a catalyst (carbon seed- pure carbon source); under the same environments (High-Pressure, High Temperature) that natural diamonds form, they grow a diamond. This process requires large machines to maintain the Pressure and Temperature needed for diamond growth.