Why Do Diamonds Sparkle? The Physics of Light in Your Jewelry

Diamonds sparkle because they bend light more strongly than almost any other clear material, split it into its colors, and send it back out through the top of the stone. Gemologists describe that light in three ways: brilliance, fire and scintillation. Under strong sun, like a bright afternoon in Miami, all three are at their most dramatic.

What makes diamond so good with light?

Every transparent material slows light down and bends it as it enters. The measure of that bending is the refractive index. Glass is about 1.5. Diamond is about 2.42, one of the highest of any natural gem. The stronger the bending, the more light can be trapped inside the stone and redirected.

That high refractive index also gives diamond a small critical angle, about 24 degrees. Light that hits an inner surface at a steeper angle than that cannot escape and reflects completely, like a mirror. A well cut diamond is designed so light enters the top, bounces off the pavilion facets underneath, and returns to your eye.

Brilliance, fire and scintillation

• Brilliance is the white light returned to your eye. It makes a diamond look bright.
• Fire is the flashes of color. Diamond spreads white light into a spectrum, the same physics as a prism, called dispersion.
• Scintillation is the sparkle that flickers when the diamond, the light or you move.

Why does the cut matter more than anything?

A diamond's carbon does the same thing in every stone, but the cut decides where the light goes. Too shallow, and light leaks out of the bottom. Too deep, and it escapes through the sides. In 1919, the engineer and gem cutter Marcel Tolkowsky published Diamond Design, calculating proportions for the round brilliant that balance brilliance and fire. Modern round brilliants still follow his ideas.

That is why, when you choose a diamond, cut quality is the first thing to look at, before size.

What about small diamonds in pavé?

Pavé means many small diamonds set close together. Each one is tiny, but together they create constant scintillation, because there is always a facet somewhere catching light. That is why the Wavy Diamond Hoop Earrings, a wave of natural diamonds curving around the ear, sparkle with every turn of your head, and why the Wavy Bow Diamond Hoops look alive on camera.

Why do diamonds look different indoors?

Direct sunlight is a point source, so it creates sharp flashes of fire. Diffuse office light makes diamonds look softer and whiter. Candlelight brings out fire. If you live in Miami, you already have the best light there is.

Margaret Krinetz Fine Jewelry, handmade in Tel Aviv and shipped to Miami, sets natural diamonds by hand so each one sits to catch light. To keep that sparkle, read how to clean gold and diamond jewelry at home.

Frequently asked questions

Why does my diamond look dull sometimes?

Usually skin oil and lotion on the back of the stone. A gentle clean brings the light back.

Do lab grown diamonds sparkle the same?

Yes. They are the same material, so sparkle depends on cut quality.

How long does delivery to Miami take?

Every piece is made to order in 4 to 6 weeks and ships with DHL Express in 3 to 5 business days. Shipping is free on orders over $1,500.

Light, bent and returned to you. Feel the freedom of being alive.