Diamond Cut

Of the 4 Cs, cut is the one that does the most work and gets the least credit. Two diamonds can carry the same carat weight and the same color and clarity grades and still look completely different side by side. Cut is almost always why.

Cut is not the same thing as shape

People use these words interchangeably, but they're not the same thing. Shape is the outline: round, oval, pear, cushion, and so on. GIA reserves an actual cut grade, Excellent through Poor, only for standard round brilliant diamonds, because round is the one shape with a facet pattern consistent enough to grade on a standard scale. Fancy shapes like princess, cushion, or emerald don't get that same Excellent-to-Poor grade on a report, because their proportions vary too much from stone to stone to standardize the same way.

What the grade is actually built from

GIA's cut grading system looks at seven components, not just one number pulled out of the air. Three are about how the diamond looks: brightness (how much light bounces back out), fire (light breaking into spectral color), and scintillation (the flashes of light and dark you see as the stone or the light source moves). The other four are about how well it was made: weight ratio, durability, polish, and symmetry. Each one gets weighed individually, and the overall grade reflects how they come together.

The anatomy of a round brilliant

A standard round brilliant has 57 or 58 facets. The flat top is the table. The bottom point (or tiny flat facet, if there is one) is the culet. In between sit the crown and pavilion, and the angles and depth of those two sections relative to each other are what determine how light enters the stone, bounces around inside it, and exits back toward your eye. Cut too shallow or too deep, and light leaks out the bottom instead of bouncing back up. That's the difference between a diamond that looks alive and one that looks flat, no matter how good its color and clarity grades read on paper.

The grade scale

GIA's cut grades run Excellent, Very Good, Good, Fair, and Poor. Each grade covers a range of proportion combinations rather than one exact measurement, which means two Excellent-cut diamonds can still look slightly different from each other and both be graded correctly. That's where personal preference comes back into the decision. A jeweller can rule out Fair and Poor for you on sparkle alone. Choosing between Excellent and Very Good is more about what catches your eye.

Where we tell clients to spend

If your budget forces a trade-off, cut is the C we'd protect first, ahead of color or clarity. A diamond a grade or two down in color or clarity can still look excellent if the cut is doing its job. A poorly cut diamond with top color and clarity grades will still look duller sitting next to a well-cut stone at a lower grade. We'll put two diamonds side by side on the same finger so you can see this for yourself. It's a fast way to understand why the grade sheet only tells part of the story.

Key Takeaways

• Cut and shape are different things. GIA issues a formal Excellent-to-Poor cut grade only for round brilliant diamonds.
• The grade comes from seven weighted factors: brightness, fire, scintillation, weight ratio, durability, polish, and symmetry.
• Crown and pavilion angles control how light enters and exits the stone, which is what separates a lively diamond from a flat-looking one.
• If budget is tight, prioritize cut over color or clarity. A well-cut stone with modest color and clarity will usually out-sparkle a poorly cut stone with top grades in both.
• Seeing two diamonds side by side under the same light tells you more than reading two grade sheets ever will.

Come see the difference in person, or browse our diamond jewellery to shortlist a few stones before your visit.