The 4Cs of Lab-Grown Diamonds

The 4Cs — cut, color, clarity, carat — were built by GIA in the 1950s to standardize how natural diamonds get priced and described. They work as a rationing mechanism. Natural supply is fixed, so the rarest grades carry the largest premium, and most buyers accept tradeoffs to land at a price they can pay. Lab-grown diamonds change that math. The same crystal, the same optical behavior, the same 10 on the Mohs scale — but supply is elastic, so the premium curve flattens. A D color, VVS2 clarity, 1.5ct stone that prices at $20,000+ in natural runs $3,000–$5,000 in lab. The 4Cs stop functioning as a rationing matrix and start functioning as a spec sheet.

This guide walks each C in the order they actually affect what you see on the hand: cut first (it is the only C that is about light), then color, then clarity, then carat. Each section has a comparison table, a note on what is specific to lab-grown stones — CVD versus HPHT inclusion patterns, growth-chamber color outcomes — and a recommendation for where to stop spending. The Sula house default at the end — D color, VVS2 clarity, GIA Excellent cut, IGI graded — is locked because at lab-grown prices the upgrade math always works out. We do not sell lower because we do not need to.

Cut is the only C that is about light. Color, clarity, and carat describe the stone's body — what it weighs, what color tint it carries, what is inside it. Cut describes how the stone returns the light that enters it. A poor-cut D VVS1 looks duller than an excellent-cut H VS2, because the duller stone is leaking light out the pavilion instead of returning it through the table.

The GIA cut grade — Excellent, Very Good, Good, Fair, Poor — only applies to round brilliant diamonds. It is calculated from polish, symmetry, table percentage, depth percentage, crown angle, pavilion angle, and a handful of other proportions. To earn GIA Excellent, every component grades Excellent. The drop-off below Excellent is steep: light return falls 8–15% at Very Good, and the stone starts to look windowed. You can see through it instead of light bouncing off it.

Sula stocks GIA Excellent only for rounds. For other shapes — oval, pear, emerald, cushion, radiant, marquise, asscher, heart — GIA does not issue a cut grade. We judge each shape against a proportional spec: oval at length-to-width 1.35–1.50, pear at 1.45–1.75, emerald at 1.30–1.50, cushion at 1.00–1.20. Polish and symmetry are graded separately on all shapes; both should read Excellent or Very Good on the IGI report. Anything below Very Good on symmetry produces a silhouette no setting can hide.

IGI's lab-grown grading uses the same proportional thresholds as GIA. The two labs are not graded against different bars; the bar is the same and the report layout differs. IGI Ideal for rounds is functionally equivalent to GIA Excellent. We accept either on rounds, and IGI Excellent — the highest grade IGI issues on non-round shapes — on fancies.

Cut quality is non-recoverable. If the proportions are off, no polishing fixes it — the rough has to be re-cut into a smaller stone. A 1.5ct GIA Excellent costs 15–20% more than a 1.5ct Very Good in lab-grown. The price gap is worth it because cut is the only spec you cannot upgrade later.

The color scale runs D (colorless) through Z (light yellow or brown). Anything past Z is fancy color — pink, blue, yellow, champagne — graded on a separate scale. Sula stocks D through F. Most US lab-grown retailers go to H. We do not, because the price difference between F and D at our volumes is too narrow to justify spreading the catalog.

D, E, F (colorless). Indistinguishable face-up to the unaided eye, even in side-by-side comparison. The only way to tell D from F is on a graded color comparator under controlled lighting. In a ring, face-up, mounted in any metal, these three read identically.

G, H (near-colorless). A faint warmth in the side view, visible against a stark white card. Face-up, still reads colorless in most lighting. The savings on H versus D on a 1.5ct round runs $400–$700 — small enough that we do not stock it.

I, J (faint). Visible warmth in side view, faint warmth face-up in cool lighting. Reads as champagne in yellow gold, which can be a deliberate styling choice. Several Australian and UK brands build whole collections on H–J in yellow gold for this reason.

K and below. Visible color even to the untrained eye. Best paired with yellow gold if at all.

A note specific to lab-grown: CVD-grown diamonds default to D–F because the chemical vapor deposition chamber does not introduce nitrogen, the trace element responsible for the yellow tint in natural stones. HPHT-grown diamonds can produce the full D–Z range but skew toward G–J unless the producer post-processes them. Sula's center stones are CVD-grown D–F, post-growth-treated where needed to remove any residual brown tone from the growth process.

Metal interaction matters more than buyers usually realize. White gold and platinum show color faster than yellow or rose gold — the cool metal contrasts with any warmth in the stone. A G-color stone in yellow gold reads as D to the eye; the same stone in platinum can look like a J. If you are set on a yellow-gold setting, the practical color floor moves from F to H without visible compromise.

Clarity grades run FL (no inclusions or external blemishes at 10×) to IF (no internal inclusions at 10×) to VVS1, VVS2, VS1, VS2, SI1, SI2, then I1–I3. The grade is assigned at 10× magnification — a jeweler's loupe — not at face-up viewing distance. What matters for a ring you wear daily is the eye-clean threshold, not the loupe grade.

Round, oval, cushion, radiant. VS2 is reliably eye-clean across virtually every stone we have cut. SI1 is eye-clean in roughly 70% of stones — if you can see the IGI plot diagram before buying, SI1 saves you $300–$500 on a 1.5ct.

Pear, marquise, heart. VS1 minimum. The pointed end shows inclusions that a round brilliant would hide behind a bezel.

Step cuts — emerald, asscher, baguette. VS1 minimum. Step facets are open windows. Anything in the stone is visible at face-up distance.

Lab-grown clarity profiles differ from natural in predictable ways. CVD diamonds tend toward pinpoint clouds and the occasional metallic inclusion — a tiny silvery speck from the chamber catalyst, usually graded as a pinpoint or needle on the IGI plot. HPHT diamonds skew toward pinpoint inclusions and faint graining (slight growth-pattern lines visible at 10×). Neither type produces the dark carbon crystals or feathers common in natural stones. In practice, lab-grown SI1 reads cleaner than natural SI1 because the inclusion types are smaller and lighter.

Sula stocks VVS2 as the house default. The reason is narrow: the price delta from VS1 to VVS2 on a 1.5ct lab-grown stone runs $200–$400. For that money, you get a report photo that is clean to the eye at 10× — meaning you stop wondering whether you will spot the inclusion ten years from now under a different light. The IGI plot is essentially blank. We do not go to VVS1 or IF because the marginal upgrade is not visible at any magnification a buyer will ever apply.

On FL and IF: both are loupe-clean at 10×, so the visual outcome is identical. The price gap exists because FL also requires no external blemishes — no polish lines, no naturals on the girdle. For a stone going into a setting where the girdle will be covered by prongs, the FL premium buys you nothing.

Carat is weight, not size. One carat equals 0.20 grams. Two stones at 1.00ct can look meaningfully different in face-up dimension because depth percentage, table percentage, and proportions vary. A 1.00ct round brilliant runs roughly 6.4–6.5mm in diameter at standard 61% depth; a deep-cut 1.00ct might come in at 5.9mm. Always read the millimeter dimensions on the IGI report, not just the carat number.

Standard face-up dimensions at common weights for round brilliant: 1.0ct ≈ 6.4mm, 1.5ct ≈ 7.4mm, 2.0ct ≈ 8.1mm, 2.5ct ≈ 8.7mm, 3.0ct ≈ 9.3mm. Oval at the same weights runs longer: 1.0ct ≈ 7.7 × 5.7mm, 1.5ct ≈ 8.5 × 6.3mm, 2.0ct ≈ 9.3 × 6.9mm. Emerald sits in between. Pear extends the longest, with 2.0ct reaching 10.2mm tip to tip.

Visual scale against Sula's locked spec — 1.8mm band width, 16.9mm inner diameter at US ring size 6.5 — gives you a quick mental check. A 1.0ct round reads dainty and balanced for size 4–6 fingers. A 1.5ct round reads as the US bridal benchmark, balanced for size 5.5–7. A 2.0ct reads bold and present, balanced for size 6.5–8. A 2.5ct and above reads as a statement piece, and the proportions work best at size 7 and up.

Finger size is correlation, not prescription. A 1.0ct on a size 8 finger does not look "too small" — it looks intentionally delicate. A 2.5ct on a size 4 finger does not look "too large" — it looks bold. Choose the carat that matches the look you want, then size the band to fit.

On bridal sets: spec sheets list either "carat" (the center stone alone) or "ct.tw" (carat total weight — combined across center plus accent stones plus wedding band). A 1.5ct center engagement ring paired with a 0.5ct.tw wedding band lists as 2.0ct.tw across the set. Always ask which metric is on the spec sheet before comparing prices. The difference can be 20–30% of the stone budget.

House Default — Locked

What every Sula center stone is, before you ask

This is the spec on every center stone we set. We chose it because at lab-grown prices the math always works out — the upgrade from a G VS1 to a D VVS2 is small enough that the spec-sheet certainty is worth more than the savings. It is not aspirational; it is the floor.