For those who appreciate coloured gemstones, lab-created diamonds made by the HPHT process are generally yellow, orangey-yellow, or brownish-yellow. Almost all are type IIb — rare in natural diamonds. Blue lab-created diamonds form by adding boron into the growth process. Pink and red lab-grown diamonds are less common and can be produced by subjecting the crystal post-growth to heat treatment processes involving heating and radiation. Colorless HPHT synthetic diamonds are challenging to create as nitrogen needs to be excluded from the growth process, so modifications to the growth conditions and equipment are required.
CVD synthetic diamonds are usually grayish or brownish. Adding a small amount of boron or nitrogen into the chamber will create yellow, pink-orange, or blue diamonds. Colorless crystals are easier to produce with this method, but they require a longer time to grow. Many CVD lab-created colorless diamonds available are believed to have been originally brown crystals decolorized by HPHT annealing. CVD synthetic diamonds are most commonly type IIa.
Fancy-coloured lab-created diamonds sell at comparatively reasonable prices compared to their natural fancy-colored diamond counterparts.
