How Fancy Colors Are Produced

Most colored laboratory-grown diamonds get their color after growth, through HPHT processing, irradiation and low-temperature annealing, while blue can be achieved during growth through boron doping — a different object, and worth knowing which one you are holding.

There are two routes. Color can be built into the crystal as it grows, by adding an element such as boron or nitrogen to the growth. Or a finished crystal can be treated afterward, changing how its atoms are arranged until it absorbs light differently. Both produce real, permanent color. They are different processes, and a laboratory report can tell you which one a stone went through.

This Operia guide explains each route, how to read a fancy color grade, and what the report says about treatment.

How are colors added after growth?

Most CVD crystals come out of the reactor with a brownish tint. The treatments that follow can remove that tint, or turn it into a fancy color. GIA’s review of CVD-grown diamonds found that the great majority of fancy-color CVD stones were pink, produced by multiple post-growth treatments of light brown starting material.

Growers often combine them. GIA has documented a 2.00-carat Fancy Deep orange and a 3.00-carat Fancy Vivid orangy pink, both CVD-grown, that “underwent multiple treatments, including HPHT processing, irradiation, and low-temperature annealing” to reach their final colors.

The result is permanent

IGI is explicit on this point. These treatments change the diamond itself, not its surface, and reversing them would take exposure to an equal or stronger process.

Which colors can be grown in?

Two, reliably, and both come from the same impurities that define diamond type. Boron added during growth produces blue: a Type IIb stone, the same chemistry our guide to diamond type traces behind blue nuance. Nitrogen produces yellow, which is why many HPHT-grown stones come out yellow without any treatment.

Controlling either is hard, and controlling both in one crystal is harder. In 2023, IGI analyzed a 4.38-carat radiant cut from Meylor Global, graded VVS2 and Fancy Deep greenish blue, Type IIb, with distinct blue and yellow zones: blue from boron doping, yellow from traces of nitrogen. IGI found no evidence of post-growth treatment, and examined it alongside a 10.96-carat rough crystal with the same zoning.

Meylor priced the stone at $4,500 per carat. A blended 5-carat colorless laboratory-grown diamond stood at about $467 per carat on a market price index as this guide was written: close to a tenfold difference, and a measure of what control over color is worth.

How do you read a fancy color grade?

A D-to-Z grade measures the absence of color. A fancy color grade measures its presence, in three dimensions: hue, the color itself; tone, how light or dark it is; and saturation, how strong it is. The grade combines the hue with a single term that describes tone and saturation together.

Vivid and Deep are the two most often confused. Fancy Vivid is the strongest saturation at a medium tone. Fancy Deep is strong saturation at a darker tone. Deep is not a stronger Vivid; it is a darker one. Meylor’s greenish blue stone is Fancy Deep.

Where fancy color begins depends on the hue. For blue, pink and green, IGI adds a comment such as “Faint Blue” or “Faint Pink” to stones in the G to J range of the colorless scale, and treats anything more saturated than J as Fancy Light.

What does the report say about treatment?

IGI’s Fancy Colored Diamond Report states that a stone is laboratory-grown, gives its fancy color designation, and grades hue, tone and saturation, along with how evenly the color is distributed. On treatment, IGI’s own wording is direct:

So a full IGI report on a colored lab-grown diamond tells you two things about treatment: whether a permanent treatment is present, and, by the fact that the report exists at all, that no impermanent treatment such as a coating is involved. On IGI’s laboratory-grown reports, the comments state the growth process and, where there is no sign of treatment, “As grown.”

What to ask for

What Operia states per stone

[OPERIA TO CONFIRM: which colors are stocked, and for each, whether the color is grown in or produced after growth]

Treated and grown-in color are both real and both permanent. They are still different objects, so each colored stone’s page states:

Shop Diamonds|Read The Operia Standard

Frequently asked questions