Diamond Cut: Why It Matters Most

No, and mixing them up is one of the most common points of confusion. Shape is the outline of the diamond, whether it is round, oval, princess, emerald and so on. Cut is how well the stone was actually made within that shape, meaning the angles, proportions and finish that decide how light travels through it and back to your eye. Two round diamonds can share the same shape yet have very different cut quality, one bright and lively, the other dull. The GIA cut grade, which runs from Excellent down to Poor, applies most precisely to round brilliants, while fancy shapes are judged more on overall proportions and your eye. So when you shop, treat shape as a style choice and cut as a quality choice, and never assume a nice shape guarantees a good cut.

Aim for Excellent or Very Good on a round diamond. These grades return the most light, so the stone looks bright and lively in everyday lighting, which is exactly what people notice about a diamond. Below Very Good, a stone starts to leak light and can look flat or glassy even if it is large and clean, so the money you spent on size and clarity gets wasted on a dull result. For fancy shapes, which are not always given a formal cut grade, judge the proportions and, most importantly, look at the stone in person, because a well-cut oval or pear simply looks alive in the hand. Whatever the shape, protect the cut before you spend on other grades, since cut is the one you cannot fake.

For how a diamond looks, yes. Cut controls sparkle, and sparkle is what draws the eye, so a well-cut smaller diamond usually looks brighter and more impressive than a larger stone with a weak cut. A poor cut hides weight in the bottom of the stone, so a heavier diamond can actually look smaller and duller across the top than a lighter, better-cut one. That is why we tell people not to chase carat at the expense of cut. Decide on an Excellent or Very Good cut first, then choose the largest carat weight your budget allows within that. You will end up with a diamond that looks lively and, often, larger for its weight. Size impresses on paper, but cut is what people actually see across a room.

Polish and symmetry are two smaller grades that sit alongside cut and describe the quality of the finishing work. Polish is how smooth the surface of the diamond is, since tiny polishing marks left during manufacture can slightly dull the surface. Symmetry is how evenly and precisely the facets are aligned, because misaligned facets can affect how cleanly light reflects. Both are graded from Excellent down, and the good news is that Very Good or better on each is plenty for almost everyone. The difference between Very Good and Excellent on polish or symmetry is genuinely hard to see without magnification, so it is not worth paying a large premium to reach the very top. Treat these as a final check after cut, colour and clarity, not as a place to spend heavily.

Move the diamond gently under normal room light and watch how it responds. A well-cut stone throws crisp, bright white flashes and looks lively and full of light from edge to edge. A weak cut tends to look flat, glassy, or dark in the centre, sometimes called a nail-head, where light leaks straight through instead of bouncing back. Tilt it, walk it under different lights, and compare it directly against another stone if you can, because side by side the difference in cut is obvious even to an untrained eye. On the grading report, start at the cut line and look for Excellent or Very Good. In our Coquitlam studio we are always happy to put two diamonds next to each other so you can see for yourself which one truly comes alive.