Daniel Howell Ph.D.
Chief Scientist and Co-Founder,
Diamond Durability Laboratory

Nitrogen is almost ubiquitous in diamonds. So much so that its rare absence is highly sort after in gem diamonds. Some estimates1 suggest that over 98% of diamonds contain detectable amounts of nitrogen. As a result, diamonds are even classified based upon the characteristics of the nitrogen that they contain. The valuable colorless Type II diamonds have nitrogen contents of about less than 10 parts per million (for every 1 million atoms of carbon that make up the diamond, less than 10 are nitrogen), while Type I diamonds have been reported to contain up to 5000 ppm (0.5%; average values ~200-300 ppm).

While nitrogen is responsible for yellow color in diamonds, it is how the nitrogen is bound in the diamond that causes the color. When nitrogen is incorporated into a diamond, a single nitrogen atom takes the place of a single carbon atom. Diamonds containing nitrogen in this form are classified as Type Ib. They exhibit yellow color because the single nitrogen atoms absorb light in the violet and blue portion of the spectrum, resulting in our perceiving the color yellow.

In the old world this type of color was commonly termed canary yellow because of its unique high yellow saturation. More recently, the term Zimmi has entered into the gem industry to refer to these yellow Type Ib diamonds. The reason...