Most people shopping for an engagement ring get shown beautiful stones. Well-lit, perfectly photographed, looking their best. Nobody shows you a bad one.
That's a problem. Because a poorly cut diamond is easy to end up with if you don't know what to look for. And once it's on your finger under normal light, in a real room, you'll notice.
Cut Is Not Shape
This is the most common mistake people make. When jewellers talk about cut quality, they don't mean whether the diamond is round, oval, or pear-shaped. That's the shape. Cut is something different.
Cut refers to the proportions of the stone. The angles. The depth. The symmetry. How all the facets, those tiny flat surfaces, relate to each other. This is what determines how light moves through a diamond.
A diamond with good proportions takes light in through the top, bounces it around inside the stone like a mirror, and sends it back up to your eye. That's what sparkle is. That's what fire and brilliance actually mean.
Get those proportions wrong, and the light doesn't bounce back. A poorly cut diamond's depth may be too shallow or too deep, causing light to leak out through the bottom or sides instead of returning to your eye as brilliance.
The result is a diamond that sits on your finger and looks flat. Dull. Dead. Even if the stone is technically flawless on paper.
What Makes a Cut Bad
There are two main ways a stone can be cut poorly, and both have the same result.
Too shallow means the stone is flat. Light enters the top, passes straight through, and exits out the bottom before it has a chance to reflect back. The diamond looks glassy and lifeless. It can also appear bigger than its carat weight suggests, which is why some stones are cut shallow intentionally. They look larger on paper while sacrificing everything that makes a diamond worth buying.
Too deep means the stone is cut like a tall cone. Light hits the bottom facets at the wrong angle, leaks out the sides, and again doesn't return to your eye. Deeper stones also look visually smaller than diamonds of the same carat weight, because the weight is buried in the depth of the stone rather than spread across the surface.
In both cases, you're paying for carat weight that isn't working for you.
The Cut Grade System
When you look at a diamond certificate from a grading laboratory, the cut is graded on a scale from Excellent down to Poor. For round brilliant diamonds, this grading is standardised and reliable. For fancy shapes like oval, cushion, or pear, no official cut grade is issued, so you have to look at the proportions yourself or work with a jeweller who can guide you through it.
An Excellent cut reflects nearly all light that enters the stone, representing roughly the top 3% of diamonds cut worldwide. A Poor cut allows most of that light to escape through the sides and bottom, leaving you with very little brilliance.
The practical advice is simple. For round diamonds, stick to Excellent. Don't go below Very Good. If budget is tight, a smaller Excellent cut stone will always outperform a larger Fair or Poor cut stone. You are buying light performance, not weight.
Why Cut Matters More Than Clarity or Colour
Most people fixate on clarity and colour when shopping. Those things matter. But cut is the factor that determines whether the stone actually performs.
Even a high colour or clarity grade will not make up for a poorly cut diamond that looks dull or lifeless. A stone graded VS1 with a good colour can still look dead on your finger if the cut is off. A stone with a minor inclusion that's cut beautifully will sparkle in a way that a flawless but poorly proportioned stone never will.
Cut first. Everything else follows.
What to Look For
When buying a diamond, ask for the cut grade on the certificate. For a round brilliant, look for Excellent. Check the depth percentage, which for a round stone should sit roughly between 59 and 62.6 percent. The table percentage should fall between 54 and 61 percent. These numbers aren't everything, but they tell you whether the proportions are in the right range.
If you're shopping online, use a retailer that shows 360-degree video of each stone. That's the only real way to assess light performance when you can't hold the stone in your hand. A well-cut diamond moves with light. A poorly cut one doesn't.
If you have questions about the cut of a specific stone you're looking at, send us a message. We're happy to look at it with you and tell you exactly what we see.
View our full collection of beautiful lab-grown diamond engagement rings that are sure to get you excited!
Thanks for reading, Jared and Brie