Why Diamonds Sparkle

Welcome to Spring

… at least as per the equinox: the sun has crossed the celestial equator, and day and night are again approximately equal.

Speaking of light:

I’ve had the good fortune of having several diamonds on my bench this week. One big guy at 2.07ct , and a smaller, very gorgeous Canadian diamond, and several ReBirth diamonds like the ones pictured here.

With the return of the light and brighter days, I am also getting more sunshine in the studio, which makes those diamonds sparkle. This reminded me of a time when my beloved mother-out-of-law was visiting the studio, and her giant diamond ring make rainbows dance all around the studio walls and ceilings!

Light’s Journey through a Diamond

But I digress.

Of course we are all familiar with the 5 C’s:

carat, cut, clarity, colour, and Canadian (!), but let’s dig deeper into the complexities of light performance. How well a diamond interacts with light affects its visual appeal. So how does that work?

Watch a 1.53ct diamond sparkle in the light:

As jewellers, we talk about ‘light performance’, which is determined by the path of light as it enters the diamond, is refracted, internally reflected, finds its path through the stone, and exits back out the top, and the visual effects this creates.

How this all breaks down is quite complex. I don’t want to keep you here all day, so I will make this very brief. It’s all about the path of light.

First, light will hit and bounce off the outside surfaces of the diamond, causing reflection.

Then, as light enters the diamond, light ‘slows down’, bending its path. This is called refraction.

Once the light is inside the diamond, it will cause ‘internal reflection’, making the diamond appear brighter by bouncing off the walls, so to speak.

Think of the path of light is like the ball in a pinball machine, with the goal of the ‘ball’ (i.e. the light) being shot back out the surface of the stone. You can imagine: only if all angles of the diamond are exactly perfectly positioned and proportioned will the light find this path.

By definition, brilliance refers to the amount of white light reflected, whereas fire is dispersed/rainbow light that flashes from inside the diamond towards the viewer.

Ok, almost done, hang in there.

Scintillation

That flashy sparkle you get when the diamond is being moved about is referred to as scintillation. A diamond will have white ‘flash scintillation’, and rainbow-coloured ‘fire scintillation.

Contrast

The last factor is contrast, which refers to dark and light areas, which act a bit like a hall of mirrors.

The Power of Cut: Why Angles Matter

This is why CUT is – for me – the primary factor when choosing a diamond: only an optimally cut diamond will get the very best light return, and thus brilliance. This is why the proportions and angles are so important.

Of course these are only the aspects referring to light. A professional will also examine more external characteristics, such as whether the diamond is actually round (many aren’t!), whether its ‘table’ is centred, the even-ness and thickness of the ‘girdle’, et cetera. And of course colour and clarity.

… and origin, if it’s a sustainable jeweller!

Bezel Settings are just as Bright as Prongs

I do want to point out here, though, that this explains why a diamond set in a full bezel isn’t any less bright than one set in prongs: in an excellently cut diamond, the light enters from and leaves again on the top and table facets.

Unfortunately it’s tough to show all this in a photograph, try as I might. Just make an appointment to come see me in the studio (virtually or in person), and I’ll show you 😉