A straight-A report card is something every parent wants to see. But for a diamond, a D is a very good grade indeed.

Why does a diamond need a report card? After all, it’s not applying to college or looking to get a job.

A diamond report card—called a certificate—is an objective evaluation of its quality characteristics. These characteristics are what determine the stone’s market value.

Many retail jewelers employ graduate gemologists on staff who are qualified to evaluate a stone’s physical qualities, but many also use a gemological laboratory to provide an independent evaluation. While there are a number of gemological laboratories in the world, the one that is recognized universally as a leader is the Gemological Institute of America in Carlsbad, CA. It’s most commonly called by its familiar acronym, GIA.

A GIA certificate describes a diamond’s physical attributes, including the Four C’s: its color, its clarity, its carat weight, and how well it’s been cut. Color grades go from D (clear as pure water) down to Z, which has very noticeable color. Clarity grades go from “Flawless” (Fl), down to “Included” (I), meaning that inclusions (tiny imperfections) are large enough to be seen by the naked eye. Cut grades range from “excellent” (displaying optimum fire and brilliance) to “poor,” which often means that the stone has been cut to retain as much carat weight as possible, but to the detriment of its natural beauty.  A certificate also can identify whether the stone is natural or laboratory-grown, and whether it’s had any enhancements or treatments.

Sample grading certificate, © GIA. Reprinted by permission.

A GIA certificate does not provide a monetary valuation for the stone. The monetary value of a stone is determined by comparing its objective physical qualities to the market and establishing a fair price based on the current state of the market. In that respect, it’s much like real estate, except that location doesn’t matter. A qualified retailer or appraiser would take the certificate, compare it to the market, then determine the value and/or set a price for the stone.

Because diamonds are graded by human eyes—whether in a lab or by a jeweler—slight variances in grade may occur between two people looking at the same stone. But these variances should be very small—within one grade—and GIA often will have several graders review a stone.  Where there are disagreements, the diamond is referred to the most experienced graders to be the “umpire” and render a final opinion.

But let’s get back to the diamond report card. Why is it so good for a diamond to get a D, when that same grade got you grounded in high school?

Simple. Until the middle of the 20^th century, there was no single consistent method for evaluating a diamond. One jeweler’s A, B, or C was another’s I, 2, or 3 was another’s 0, 1, or 2—which made it very difficult to determine market value. In the early 1950s, GIA developed its International Diamond Grading System, now the global standard. But to set itself apart from all other grading methodologies in use at the time, GIA chose D as the top grade for its color scale. It also, incidentally, leaves room at the top in case someday some intrepid explorer unearths a diamond whose color is better than the best anyone has yet seen.