Clarity

Clarity measures the absence of inclusions and blemishes inside and on the surface of a diamond. Every natural stone forms under extreme pressure and heat, and almost every stone carries tiny mineral traces, internal fractures, or growth structures from that process. These are inclusions. Marks on the external surface — scratches, nicks, naturals — are blemishes. Clarity grading assesses both, using a standardised ladder originally codified by GIA in the 1950s.

The 11-grade ladder

The boundary that matters most in commercial trading sits at SI1 / SI2. Everything above it is reliably eye-clean in commercial sizes; everything below it is not. That single line is where the bulk of value optimisation happens.

How clarity is graded

Graders evaluate clarity under 10× magnification with controlled lighting, looking at the stone from multiple angles — face-up through the table, through the pavilion, and from the sides. They catalogue inclusions by type, count, size, position, and effect on transparency and durability, then assign an overall grade. The process is systematic, but the final grade carries a subjective component: the same stone can receive a slightly different grade from two graders, or from the same grader on two different days.

Every certificate from a major lab includes a plot — a schematic drawing of the stone with inclusions marked in their actual positions. Red marks denote internal inclusions; green denotes surface blemishes. The plot is often more useful than the grade letter itself, because it tells the buyer where the inclusions sit and whether they will be visible face-up or masked by the setting.

What inclusions look like

Inclusions come in recognisable types, each with its own grading weight:

• Pinpoints — tiny mineral crystals appearing as dots at magnification. Individually harmless; in large numbers they form a cloud that slightly reduces transparency
• Crystals — larger mineral inclusions, usually dark garnet or diopside. More visually disruptive than pinpoints
• Feathers — small internal fractures, appearing as curved or jagged lines. Flat feathers parallel to the table catch light and become visible as white reflections
• Needles — long thin crystals, occasionally grouped
• Twinning wisps — faint ribbon-like growth structures along twin planes, typically harmless
• Clouds — dense groups of pinpoints; large clouds can compromise transparency and give the stone a hazy appearance
• Naturals — remnants of the rough surface left on the girdle during cutting, counted as blemishes
• Cavities — small pits in the surface, usually a durability concern

The type and location matter as much as the count. A single feather in the centre of the table is more detrimental than a cloud at the girdle edge, even though the latter contains more inclusions by count.

Step through the ladder and toggle between Naked eye and 10× loupe views. The key observation: from FL through VS2, the naked-eye view is identical — a clean stone. Only when you switch to 10× do the grades start to separate. This is exactly how a commercial buyer experiences the difference: they can't see it without a loupe, and most of the time they don't need to.

At SI1, the first naked-eye mark appears. At SI2, a second shows up. Below SI2 — the I grades — the inclusions are visible without any magnification at all.

The eye-clean boundary

The most valuable concept in clarity sourcing is eye-clean — whether the stone's inclusions are visible to the unaided eye at a normal viewing distance (roughly arm's length).

For commercial sourcing, the payoff is concentrated at SI1: roughly half to two-thirds of SI1 stones are eye-clean, and they trade at a material discount to VS2. A well-chosen eye-clean SI1 can look face-up identical to a VS1 at 15–25% less per carat. Experienced buyers cherry-pick SI1 goods by reading plots — rejecting stones with centre-table inclusions, accepting stones with inclusions near the girdle or under the crown.

SI2 eye-clean hunting is a more speculative play: only a small fraction of SI2 goods are eye-clean, but those that are trade at 30–45% below VS1 pricing. It requires individual inspection of every stone and a relationship with a supplier who will let you return rejects.

How the market prices clarity

Clarity premiums compress at the top and stretch at the bottom. The gap between FL and IF is almost pure price — no buyer sees the difference. The gap between VS2 and SI1 is psychologically large but often visually zero. Below SI2 the gaps become real, visible, and economically justified.

Clarity and stone size

Inclusions read more heavily in larger stones. A one-carat SI1 with a centre crystal may be perfectly eye-clean because the face is small enough that the inclusion sits near the limits of unaided vision. The same relative inclusion in a three-carat stone is scaled up — the diamond is larger, the inclusion is larger in absolute terms, and the eye catches it immediately.

Practical consequence: clarity grades translate differently across sizes.

• Sub-0.50 ct: VS2 and SI1 look identical face-up; SI2 is often eye-clean. Commercial goods live in SI1–SI2
• 0.50–1.00 ct: SI1 eye-clean rate roughly 60–70%; worth selecting
• 1.00–2.00 ct: SI1 eye-clean rate drops to ~40–50%; plot-reading becomes essential
• 2.00 ct+: SI1 becomes risky without inspection; most buyers target VS2 or better; at 3 ct+ the standard moves up to VS1

The rule of thumb: for every whole-carat step upward, move one clarity grade up to maintain the same face-up appearance.

How clarity interacts with cut

A well-cut stone returns so much light that face-up inspection becomes a scintillation dance — the eye struggles to fix on any single point long enough to resolve an inclusion. A poorly-cut stone is flatter and more transparent; inclusions are easier to spot.

This means cut quality partly masks clarity weakness. A well-cut SI1 can outperform a mediocre VS2 in face-up appearance because the buyer's eye never settles on the inclusion long enough to register it. Pricing models don't formally reward this, but experienced trade buyers factor it into individual stone selection.

Practical sourcing notes

• Read the plot before the grade. A VS2 with a centre-table feather can face up less clean than an SI1 with a girdle-edge crystal. Position matters
• Build SI1 eye-clean inventory through trusted suppliers. The stones that matter are the ones with plots favourable to face-up appearance — you can't buy them algorithmically
• For investment-grade goods, stay above VS1. Resale and auction markets reward certificate prestige; below VS1 the discount to liquidation widens
• Fluorescence can help in SI goods. Medium or Strong blue fluorescence can slightly obscure small yellow-brown crystals at the SI level — a secondary but measurable effect in favour of the stone's appearance
• Watch for "cloud grade-making". A stone whose clarity grade is driven by a large cloud rather than discrete inclusions may be formally SI1 or SI2 but present as hazy in face-up viewing, which is more damaging than a single point feather. The lab report usually includes a "Clarity characteristics: cloud" note — treat it as a caution flag

Related

• Carat — clarity grades translate differently across sizes
• Color — the other half of the optical quality picture
• Cut — why well-cut stones mask inclusions face-up