Have you ever stood under soft lighting, mesmerised by a diamond that seemed to catch light from every angle and shoot it back in a dazzling firework of sparkles? I certainly have. Years ago, while helping a close friend choose an engagement ring, we walked into a tiny jeweller’s shop in Hatton Garden. The moment the jeweller tilted a round brilliant diamond under the spotlight, we both gasped. It was like holding a tiny star. But what made that diamond sparkle more than the others?

This isn’t just a matter of personal taste or marketing hype. The way a diamond is cut affects how it interacts with light—and therefore, how much it sparkles. And if you’re about to invest in one, understanding this can be the difference between an ordinary rock and a radiant showstopper.

Why Diamond Sparkle Matters

The sparkle, technically referred to as a diamond’s “brilliance,” is what most people fall in love with. It’s not just about looking pretty—it’s about how that light show evokes emotion, status, and personal taste. In fact, studies from the Gemological Institute of America (GIA) suggest that sparkle is one of the top three factors consumers consider when choosing a diamond, alongside clarity and carat weight.

So, what really determines how sparkly a diamond is?

The Science Behind the Sparkle

Diamond sparkle is influenced by three main optical effects:

1. Brilliance

The white light reflected from the surface and interior of the diamond.

2. Fire

The dispersion of light into the colours of the rainbow.

3. Scintillation

The flashes of light and dark when a diamond or the observer moves.

These effects are largely dictated by how well the diamond is cut—not its shape, size, or even colour.

So, Which one Cut Sparkles the Most?

Round Brilliant Cut: The Undisputed Sparkle Champion

There’s no contest here. The round brilliant cut reigns supreme when it comes to sparkle.

Designed with 58 meticulously placed facets, the round brilliant is mathematically optimised to reflect the maximum amount of light. In fact, Marcel Tolkowsky, a mathematician, created a precise formula in 1919 for the ideal proportions of this cut—and it’s still followed today.

Why it sparkles so much:

• Symmetrical shape allows even light distribution.
• High facet count maximises light reflection.
• Decades of refinement have made this cut almost perfect for brilliance.

Princess Cut: Square Brilliance with a Modern Twist

The princess cut is the second most popular cut, especially for engagement rings. With 57 or 76 facets depending on the variation, it gives off intense sparkle, particularly in the centre.

What to watch for: Its sharp corners can be prone to chipping, and its sparkle isn’t as consistent across the entire surface as the round cut.

Cushion Cut: Vintage Sparkle with Soft Edges

Reminiscent of old mine cuts, cushion cuts offer a softer, more romantic sparkle. Though not as blindingly bright as a round brilliant, many people love its “chunky” flashes of fire.

I once compared a cushion cut with a round brilliant under natural sunlight. The cushion reflected broader, slower flashes, almost like candlelight. It was less intense but deeply captivating.

Radiant Cut: All-Around Sparkle

Combining the best of both the emerald and round cuts, the radiant cut has a square or rectangular shape with brilliant-cut facets. It’s versatile and sparkly, often chosen for its ability to hide inclusions well.

Oval, Pear, and Marquise Cuts: Elegant but Uneven Sparkle

These elongated shapes can be striking, but they often suffer from the dreaded “bow-tie effect,” where a dark shadow appears across the centre. While they still sparkle, it’s usually not as consistently bright as round or princess cuts.

Expert Insight: What Gemmologists Say

According to GIA gemmologist Dr. Loretta Weathers, “Cut quality is the single most important factor influencing a diamond’s brilliance. A poorly cut diamond will look dull even if it has perfect clarity and colour.”

She adds that many buyers mistakenly focus on carat size or clarity, overlooking cut—which can be a costly error if sparkle is what you’re after.

Real-World Advice: How to Choose the Sparkliest Diamond

1. Prioritise Cut Quality Over Carat or Clarity

Always go for an Excellent or Ideal cut grade, especially for round brilliants.

2. View the Diamond in Different Lighting

Jewellery shops use flattering lighting. Ask to see the stone in natural light or use a sparkle-scope.

3. Don’t Rely Solely on Certificates

Certificates give data, not beauty. Two diamonds with the same grades can look vastly different in person.

4. Ask About Light Performance Reports

Some sellers offer ASET or Idealscope images that show how well a diamond handles light.

Related: Can Diamonds Break? The Truth Behind the World’s Hardest Gemstone

FAQ: Quick Answers to Common Questions

Which diamond cut has the most brilliance?

The round brilliant cut has the most brilliance, thanks to its symmetrical shape and ideal facet pattern.

Is sparkle more important than clarity?

In many cases, yes. A slightly included diamond with excellent cut will sparkle more than a flawless one with poor cut.

Do larger diamonds sparkle more?

Not necessarily. A bigger diamond with a poor cut can appear dull compared to a smaller, well-cut one.

What’s the best cut for maximum sparkle on a budget?

Look for smaller round brilliants with Ideal cuts. Consider lab-grown diamonds to maximise value.

Final Thoughts: Choose Sparkle That Speaks to You

At the end of the day, the diamond that sparkles the most technically is the round brilliant cut. But the one that shines the most for you might be something different. Maybe it’s the candlelit charm of a cushion cut or the bold shape of a marquise.

If I’ve learned anything, it’s this: sparkle isn’t just science. It’s also emotion, memory, and meaning. So when you choose your diamond, don’t just look for the one that shines the brightest. Look for the one that lights you up inside.

Have you recently picked out a diamond? What cut spoke to you and why? Drop your story in the comments below — I’d love to hear it.