Essential Read · 8 min
The 4Cs of
Diamond Quality
In 1953, GIA created the universal diamond grading system: Cut, Colour, Clarity, and Carat. Every diamond certificate you see — whether GIA or IGI — uses these four criteria. Understanding them will transform the way you shop for diamonds.
Cut
Cut is the most important of the 4Cs. It refers not to a diamond's shape, but to how well its facets interact with light — its proportions, symmetry, and polish. A perfectly cut diamond returns almost all incoming light back to your eye as brilliance (white light), fire (rainbow flashes), and scintillation (sparkle when moving).
Even a D Flawless diamond will look dull with a Poor cut. Never compromise on cut.
Maximum brilliance and fire. Light returns through the table perfectly. The top 3% of diamonds.
Superb light performance with minor imperfections that are invisible to the naked eye.
Most light reflects through the crown. An excellent choice for budget-conscious buyers.
Some light leaks from the sides. Acceptable for smaller accent stones.
Significant light leakage. Avoid for a centre stone.
Smilvin recommendation: Always choose Excellent cut for round brilliants. For fancy shapes (oval, cushion, pear), use Very Good or Excellent polish and symmetry as your guide.
Colour
GIA grades diamond colour on a scale from D (colourless) to Z (light yellow or brown). The differences between adjacent grades are subtle — even trained gemologists use master comparison stones under controlled lighting. In real-world settings, the colour difference between G and H is nearly impossible to detect.
The rarest and most valuable. Completely colourless even under magnification. Best with platinum/white gold.
Colour nearly impossible to detect without comparison stones. Excellent value. G and H are our top picks.
Slight warmth detectable face-up in larger stones. Beautiful in yellow/rose gold settings where the warm hue blends.
Noticeable colour. Only consider if working with a tight budget and a warm-metal setting.
Clarity
Clarity measures the presence of natural imperfections — called inclusions (internal) and blemishes (external) — that formed when the diamond crystallised deep within the earth. Almost all diamonds have some, which is what makes each stone unique. The key question is: are they visible to the naked eye?
No inclusions or blemishes under 10× magnification. Extremely rare — less than 0.5% of gem-quality diamonds.
Inclusions are minute and extremely difficult for a skilled grader to see. Virtually eye-clean.
Minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) to see at 10×. Eye-clean. Best value zone.
Inclusions are noticeable under 10× magnification. SI1 is usually eye-clean. SI2 may be visible to the naked eye.
Inclusions visible to the naked eye. Not recommended for fine jewellery centrestones.
Smilvin recommendation: VS1 or VS2 offers the best value for most buyers — eye-clean stones at a significant saving over VVS grades. For smaller stones under 0.5ct, SI1 is often perfectly eye-clean.
Carat
Carat is a unit of weight, not size. One carat equals 200 milligrams (0.2 grams). Because density varies between diamond shapes, two 1ct diamonds can look different sizes. A round brilliant 1ct is approximately 6.5mm across. An oval 1ct might measure 7.5×5.5mm, appearing larger face-up.
Price increases exponentially with carat weight because larger diamonds are rarer. A 2ct diamond is not twice the price of a 1ct — it can be 3–5× the price.
Smart tip: Consider a “shy weight” diamond — a stone just under a round number (e.g., 0.95ct instead of 1.00ct, or 1.90ct instead of 2.00ct). These are visually indistinguishable but can save 15–20% on price.
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