Diamond guide
Every diamond is described by the same four measures, known as the 4Cs. This guide walks through them using a real 0.71 carat round brilliant as the example.
Diamond color is graded on a scale from D (colorless) to Z (light yellow or brown). The differences between neighboring grades are so small they're judged against master stones under controlled light.
The example stone is a J, the last grade in the near colorless range. Face-up in a ring it looks white to most people, and it typically costs noticeably less than a G or H of the same size.
Why it matters for value: a single color grade can shift price meaningfully, which is why an appraisal grades color rather than estimating it.
Nearly every diamond forms with tiny internal features, called inclusions, and surface marks, called blemishes. Clarity grades how visible they are at 10x magnification.
The example stone is VS2, very slightly included. Its report plots a small feather, a crystal and a few pinpoints, all internal, plus a natural at the edge. None of these are visible without magnification.
Cut is the only C shaped by human hands. It grades how well a round brilliant's angles, proportions and finish return light as brightness, fire and sparkle.
The example stone is Very Good, with Excellent polish and Very Good symmetry. A well-cut J can look brighter and larger than a poorly cut G.
Polish and symmetry are graded on the same five-step scale and appear on every lab report under additional grading information.
Carat is weight, not size. One carat equals 0.2 grams, and each carat divides into 100 points, so the example stone at 0.71 carat is a "71 pointer."
It measures 5.65 to 5.69 millimeters across and 3.54 millimeters deep. Two stones of the same weight can face up at different sizes depending on how they were cut, which is why an appraisal records measurements as well as weight.
Prices jump at popular weights like 0.50 and 1.00 carat. A 0.90 carat stone can look nearly the same as a 1.00 carat for considerably less.
Proportions
A round brilliant works like a hall of mirrors. Light enters through the top, bounces off the angled pavilion facets underneath, and comes back up to your eye. Cut too shallow or too deep, and light leaks out the bottom instead.
The example stone's 36.5° crown and 41.0° pavilion sit in a classic range for bright, lively stones. An appraisal records these numbers because they affect how a diamond looks and what it's worth.
Good to know
A grading report from a lab like GIA describes the diamond: its weight, grades and measurements. By its own terms it is not a valuation. An appraisal uses those facts, plus the setting, metal and condition, to put a documented value on the whole piece.
Good to know
An insurance replacement value reflects what it would cost to buy a comparable piece new at retail. If you sell the same piece, buyers typically pay well below that. Neither number is wrong; they answer different questions.
Ready when you are
Matthew grades every stone this way at your home, then documents its value in a signed report.
