The two main methods used to create lab-grown diamonds are High Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD). In both methods, a small diamond seed is placed in an environment where it can grow into a larger diamond. HPHT uses high pressure and high temperature to mimic the conditions found deep below the earth's surface where natural diamonds are formed. CVD involves depositing carbon atoms onto the diamond seed in a low-pressure chamber, gradually building up the size of the diamond.