There are several reasons that diamonds sparkle, and they do sparkle beautifully. In fact, without that evocative glitter, it is highly unlikely that diamonds would be anything like as popular as they are today! But what are those reasons? Let us look at them.
Cut Right
Rough diamonds hardly sparkle at all. There are stories of fortuitous discoveries when a loose rough diamond caught the eye of a hopeful prospector by glinting more than the average piece of quartz would in a ray of sunshine, but these stories are few and far between, with more people deriding rough diamonds as being rather plain, if not outright ugly, greyish pebbles. It is only when a diamond has been carefully cut that its true sparkle is released – and a skilled cutter can do wonders with a good quality diamond!
Play of Light
Much of what creates the sparkle in a diamond comes down to light. There are several ways the light reacts with the diamond.
Reflection: the light simply bounces off the diamond, creating a momentarily glint or twinkle
Refraction: the light goes into the diamond, but then bounces around inside the stone. This internal reflection almost gathers light in the same way that a snowball gathers snow, releasing all the light out of the table, or the top of the diamond, in a glorious light display that seems almost magical.
Fire: some of the light moving around inside the diamond is split, rather like a prism splits white light, into a rainbow display that glitters around the outside of the stone – a rainbow halo or aura that is especially beautiful and one of the reasons for diamonds' enduring popularity.
Brilliance: this is the term given to the way a well-cut will channel the light through one facet of the diamond (usually the table) seeming to pour out more light than is available.
Scintillation: is the contrast between light and dark shown by the facets as well as the total sum of brilliance and fire – a twinkling array of glittering white and rainbow light that almost disguises the shape of the stone by surrounding it with a light display in miniature.
Clarity
The clarity refers to the inner purity of the stone. Internal fractures and flaws will affect the play of light within the stone, sending reflections off in awkward directions and ruining the symmetry that makes a good cut so effective in channeling light around the diamond.
Beautifully Cut
It is the cut of a diamond that enhances much of the sparkle that we see. The round brilliant cut, in particular, was designed mathematically, taking into account the behavior of light when passed through the specific density of a diamond. Each of the 57 facets is designed to readily drink in as much light as possible, directing and bouncing it around inside the stone until it can be released through the top, to create a wonderfully eye-catching sparkle. Other cuts create similar effects, and the cut can be used to disguise flaws inside the stone as well as to enhance the flow of light within it.
And now you know what makes diamonds sparkle so beautifully. Fortunately, this in not one of those things where knowing how it works ruins the effect!