About Diamonds

Diamonds are graded across four characteristics - Carat, Color, Clarity, and Cut. Of these, Cut is the only one that depends on the cutter's skill rather than the rough; the other three are intrinsic to the stone.

Carat - weight, not size

1 carat (ct) = 200 mg (0.2 g) = 100 points. Carat is weight, so two stones at the same carat can look different sizes depending on cut depth. Common trade ladder: 0.30 · 0.50 · 0.70 · 1.00 · 1.25 · 1.50 · 2.00 · 3.00+. The whole and half-carat marks ("magic sizes") carry a 5-15% premium over the carat just below - a 0.99ct is structurally identical to a 1.00ct but often 10% cheaper.

Color - D through Z

The GIA scale runs from D (absolutely colorless, rarest) to Z (light yellow). Below Z, the diamond moves into the fancy-color scale (see below). The shift across the scale is gradual - most untrained eyes can't tell D from G, but H from K is visible side by side.

Clarity - FL to I3

Graded under 10× magnification by trained graders. Position of an inclusion matters as much as the grade - a central SI1 is more visible than a girdle-edge SI2.

Cut - proportions, symmetry, polish

The most important C for brilliance. GIA grades cut for round-brilliants as Excellent · Very Good · Good · Fair · Poor. "Triple Excellent" = Excellent Cut + Excellent Polish + Excellent Symmetry - the benchmark for top-tier rounds, commanding 5-10% premium over single-Excellent.

Fancy shapes are not Cut-graded by GIA. They receive only Polish + Symmetry grades. Judge cut quality on fancy shapes via L/W ratio (see Shapes below), table %, depth %, bow-tie severity (ovals/pears/marquises), and window / fish-eye effects on shallow stones.

Below Z on the regular color scale, or in any non-yellow/brown hue, diamonds are graded on the fancy color scale. Color is evaluated on three axes: hue (the actual color), tone (lightness/darkness), and saturation (intensity of the hue).

GIA intensity scale

Reads left to right from least to most saturated. The same hue at "Fancy Vivid" can cost 5-10× the price of "Fancy Light."

Color families

Approximate hue palette below. Actual stones vary by tone + saturation. Many fancy colors result from trace elements (boron → blue, nitrogen → yellow), structural defects (pink, brown), or natural irradiation (green).

Natural vs treated color

Many off-white diamonds are treated to enhance or change color. Common methods:

• HPHT (High Pressure / High Temperature): turns brownish stones near-colorless, or saturates fancy yellows/greens. Permanent. Must be disclosed on cert.
• Irradiation: gamma-ray or electron-beam exposure produces blues, greens, and (with annealing) other colors. Permanent. Must be disclosed.
• Coating: thin film of color applied to the pavilion. Not durable; cleans off. Must be disclosed.

Natural-color stones command a steep premium over treated equivalents - often 3-10× depending on hue. Always require origin-of-color disclosure on the cert.

Fewer than 2% of all natural diamonds qualify as Type IIa - the chemically purest form of diamond, with no measurable nitrogen impurities. They are also the most highly prized. Many of the world's most famous historical stones are Type IIa: the Cullinan, the Koh-i-Noor, the Lesedi La Rona, the Graff Pink (a rare Type IIa pink).

What makes them rare

Most diamonds (Type Ia) contain trace nitrogen aggregated through the crystal lattice. Type IIa stones formed under conditions that excluded nitrogen almost entirely - they are essentially pure carbon. The result is a stone that often face-up brighter than its color grade alone would predict, with exceptional optical transparency to UV.

How they're identified

• UV transparency - Type IIa diamonds transmit short-wave UV light (most diamonds absorb it). A short-wave UV lamp gives an initial screening.
• Fluorescence - typically inert (None) under long-wave UV.
• FTIR spectroscopy - Fourier-transform infrared spectroscopy is the definitive lab test; checks for the absence of nitrogen absorption peaks.
• GIA Type IIa Verification - issued as a separate document or noted in the Comments section of the main grading report.

Trade value

About 25-35% of natural diamonds fluoresce under long-wave UV (commonly blue). GIA grades fluorescence as None · Faint · Medium · Strong · Very Strong.

Test in daylight + UV before buying. Maybe 1 in 10 strong-fluorescent stones shows the haze problem; the rest are fine.

All treatments must be disclosed on the cert. Treated stones are legitimate inventory at the right price - but never sell as natural.

Always trade on cert. Without one, every stone is a guess. The major labs differ in grading strictness and what they grade.

What's on a cert

• Report number (unique, verifiable via lab's online lookup)
• Shape + measurements (mm × mm × mm)
• Carat weight
• Color + clarity grades
• Cut grade (rounds only) + Polish + Symmetry
• Fluorescence
• Inclusion plot (clarity diagram)
• Proportions diagram (table %, depth %, crown angle, pavilion angle, etc.)
• Comments (laser inscriptions, treatments, origin claims)

Always verify the cert. GIA: gia.edu/report-check · IGI: igi.org/reports · HRD: hrdantwerp.com.

A GIA report (or any major lab cert) is a structured technical document. Each section answers a specific question about the stone. Here's the trader's read.

1 · Header

2 · Measurements

Three numbers in millimetres: length × width × depth. For round brilliants the report shows min-max diameter (round stones aren't perfectly circular). Compute L/W ratio yourself and cross-check against the shape's ideal range.

3 · The 4 Cs panel

• Carat weight - two decimal places (e.g. 1.07 ct)
• Color grade - D through Z (or fancy color hue + intensity)
• Clarity grade - FL through I3
• Cut grade - Excellent / Very Good / Good / Fair / Poor (rounds only; fancy shapes are not cut-graded)

4 · Additional grading information

• Polish - surface-finish grade
• Symmetry - facet-alignment grade
• Fluorescence - strength + colour (e.g. "Medium Blue"). Read against the stone's color band - see the Fluorescence section.

5 · Proportions diagram

A side-view illustration of the stone with the key proportions labelled. Watch these:

6 · Clarity plot

Top + side-view diagrams of the stone with inclusions and blemishes marked. Red marks are internal inclusions; green marks are external blemishes (naturals, polish lines). Two stones with the same clarity grade can read very differently depending on where the marks sit - always check the plot, not just the letter.

7 · Comments - always read this section

The plain-English notes the lab adds. Look for:

• Treatments - HPHT, irradiation, fracture filling, laser drilling. F. BINSABBAR rejects all of these.
• Type IIa designation - premium chemical purity (see the Type IIa section above).
• Additional clouds / pinpoints - "Additional pinpoints are not shown" or "Clarity grade is based on clouds that are not shown" - both mean there's more in the stone than the plot reveals.
• Surface graining / internal graining - affects optics in extreme cases.

8 · Inscription

Most GIA-certified stones have the report number laser-inscribed on the girdle (visible under 10× magnification). Match the inscription to the report number - that's how you confirm the cert is for this stone, not a different stone with a fraudulently-attached cert.

9 · Security features

• Holographic security pattern visible at angles
• Microprint that becomes visible under magnification
• QR code linking to the lab's verification page

The plot on a cert is a top-and-bottom-view diagram of the stone with inclusions marked. Red = internal inclusions; green = external blemishes.

Common inclusion types

Reading the plot

The plot is a top + side view diagram showing where inclusions sit. Position matters as much as size - two SI1 stones can look very different.