Lab-Grown Diamond Treatments

Not every lab-grown diamond comes out of the growth chamber looking its best. Some, particularly those grown by CVD, emerge with a brownish or greyish tint. To improve their colour, they are given a further treatment after growth, most often high pressure and high temperature annealing, which changes the crystal’s structure and removes much of the tint.

Other treatments, such as irradiation followed by heating, are used to create fancy colours like pink and blue.

Grading laboratories examine lab-grown diamonds for signs of treatment and note what they find. A report may state that the diamond is as grown, meaning no post-growth treatment was detected, or note indications of post-growth treatment. The report also states the growth method.

Always read this line. It is the only reliable way to know, since treated and untreated diamonds look the same to the eye.

The colour improvement from HPHT annealing is permanent and stable: it will not fade or change in normal wear. A treated diamond is still a diamond, graded on the same scale.

For some people that is enough. Others prefer an as grown stone, one whose colour comes entirely from how it grew, much as some people prefer an untreated sapphire. Both are legitimate positions. What matters is that the treatment is disclosed and that you choose knowingly.

Most vividly coloured lab-grown diamonds owe their colour, at least in part, to treatment after growth. The colours are stable in normal wear, though it is wise to tell any jeweller working on the ring that the stone is treated, since extreme heat, such as from a repair torch, can affect some treated colours.

Ask for the report, find the line about treatment, and decide what it means to you. If an as grown stone matters, say so at the start, since it narrows the choice. If it does not, a treated stone of the same grade will look identical on the hand.