Diamonds: the 4Cs, Carats and GIA Certificates
A diamond's value comes from four qualities known worldwide as the 4Cs: cut, color, clarity and carat weight. They are graded on the scale of the Gemological Institute of America (GIA).
Carat weight
The carat is a measure of weight: 1 carat is 0.2 grams. Larger stones are rarer, so the price rises faster than the weight: a 1-carat diamond usually costs clearly more than two 0.5-carat stones of the same quality. Approximate diameter of a round brilliant:
| Weight | Diameter |
|---|---|
| 0.25 ct | ≈ 4.1 mm |
| 0.30 ct | ≈ 4.3 mm |
| 0.50 ct | ≈ 5.2 mm |
| 0.75 ct | ≈ 5.8 mm |
| 1.00 ct | ≈ 6.5 mm |
| 1.50 ct | ≈ 7.4 mm |
| 2.00 ct | ≈ 8.2 mm |
Color
Color is graded from D to Z: D is completely colorless, and toward Z a visible yellowish tint appears.
- D, E, F: colorless, the rarest.
- G, H, I, J: near colorless; once set, they are hard to tell from colorless stones.
- K and below: a faint tint.
Clarity
Clarity shows whether a stone has natural inclusions and how visible they are under 10× magnification:
- FL, IF: flawless; FL has nothing inside or on the surface, IF nothing inside.
- VVS1, VVS2: very, very small inclusions, hard to find even under a loupe.
- VS1, VS2: very small inclusions, invisible to the eye.
- SI1, SI2: small inclusions, visible under a loupe.
- I1, I2, I3: inclusions visible to the eye.
Cut
Cut is the only one of the 4Cs that depends on the craftsman rather than on nature. The proportions and symmetry of the facets decide how much light the stone returns to the eye, that is, how brightly it sparkles. GIA grades the cut of round diamonds from Excellent to Poor. The shape (round, oval, pear, marquise, emerald cut, radiant) is a matter of taste.
The GIA certificate
A GIA certificate (GIA Diamond Grading Report) is the independent finding of the Gemological Institute of America's laboratory on one particular stone: its weight, measurements, color, clarity, cut and report number. The report number is often laser-inscribed on the girdle, the stone's thin outer edge. You can check a certificate by its number on GIA's website (Report Check).
MJ. engagement rings carry diamonds from 0.30 ct, including GIA-certified stones. The color, clarity and certificate of each stone are listed on the piece's page.
Engagement and wedding rings · Diamond rings · Earrings · Gold purity: 375, 585 and 750