The diamond library

A guide to diamonds.

One chart for each idea. The letters are GIA’s. The opinion is ours.

Color.

Color, in a white diamond, is the absence of it. GIA grades that absence from D to Z, table-down, against masterstones. Face-up in a ring, D through F are the same conversation. Most of the rings we make live in G–H for white metal, I–J for yellow.

GIA color scale, D through Z, from colorless to light
Slide · Gemological Institute of America
GIA D-to-Z color examples, table-down, grades D, H, N, and Z
Gemological Institute of America

Clarity.

Clarity is a map of the crystal, read at ten times magnification. On the hand, Flawless and VS2 can be the same picture. We ask if it is eye-clean, then we put the loupe away.

  • GIA clarity diagram, VVS2

    VVS2

  • GIA clarity diagram, VS2

    VS2

  • GIA clarity diagram, SI2

    SI2

  • GIA clarity diagram, I2

    I2

GIA published these four. The other grades are read from the report, not from a second picture.

Cut.

Cut is the only C that is a craft. It is what turns the crystal into light. GIA grades Excellent through Poor on round brilliants. Fancy shapes receive polish and symmetry. We start every conversation here.

Gemological Institute of America
GIA anatomy of a diamond, with the parts of a round brilliant
Gemological Institute of America

Carat.

Carat is weight, not size. A metric carat is 200 milligrams. A 0.99 and a 1.00 can look the same. The price does not. Buy the spread, not the number.

GIA carat weight comparison, half carat through five carats
Slide · Gemological Institute of America

Fluorescence.

Some diamonds answer a lamp you cannot see. GIA grades that answer None, Faint, Medium, Strong, or Very Strong, under long-wave ultraviolet at 365 nanometers. Blue is the usual color. It is not simply good or bad. We have not photographed the lamp, and we will not tint a stone and call it one.

  • None

    No reaction under the lamp. The usual line on a report. Neither better nor worse.

  • Faint

    A whisper, almost always blue. Invisible once the stone is set. We sit with Faint the same way we sit with None.

  • Medium

    Visible under the lamp, rarely in daylight. On a lower color, about H through M, medium blue can offset a little yellow and make the face look whiter in sun. Not a defect. If the report names a color other than blue, we say so.

  • Strong

    Clear under the lamp. In D through F, strong blue often trades at a modest discount — buyer caution, not a flaw in the crystal. We still take it to a window.

  • Very Strong

    The intense reaction. A hazy or oily look is uncommon, and almost always here rather than across the scale. We do not skip the window.

The report.

A grading report is a trained stranger’s description of the stone. It is not the diamond. We still sit with it, and we still verify the number on the laboratory’s own site.

GIA wrote the 4Cs so a diamond could be described without theatre. We prefer GIA for natural diamonds. For laboratory-grown, GIA or IGI, with the origin in plain language.

GIA Diamond Grading Report 2231048162, a 0.70 carat round brilliant
A real GIA report

The number is at the top, and the same number is inscribed on the girdle. Enter it at gia.edu/report-check, or at igi.org for a laboratory-grown report. If it does not resolve, the conversation stops.

Questions we hear.

What is a diamond certification?

A laboratory grading report. A trained stranger’s description of the stone under laboratory conditions — the 4Cs, fluorescence, measurements, and a plot of inclusions. It is not the diamond. We still sit with the stone, and we still verify the number on the laboratory’s own site.

Why is a grading report necessary?

So two rooms can speak the same language. Without a report, color and clarity are theatre. With one, we can disagree about beauty — never about the letters.

Which laboratory do we prefer?

GIA for natural diamonds. For laboratory-grown, GIA or IGI, with the origin stated in plain language. If the number does not resolve on the laboratory website, the conversation stops.

Are certificates and grading reports the same?

A grading report describes the stone. A ‘certificate’ from an unknown lab is often a sales document. We do not treat them as equivalent.

What is the most sought-after grade?

There isn’t one that belongs on every hand. Cut is where we start — Excellent on a round. Color and clarity are decided in metal, on skin. D Flawless is a laboratory trophy. Most of the rings we make live in G–H, VS, and look colorless and silent on the hand.

Why sit with us?

Because the paper cannot hold character. We match every side stone to the center — lab or natural. We make 14k through 22k, rose, yellow, white, platinum. We will spend the 4Cs on the one you keep looking at.

Featured

The atelier

A round brilliant in platinum on white

Every diamond is evaluated to the 4Cs. The rest is done with the stone in front of you — in the room or on a call, natural or laboratory-grown, every shape.