Why Does A Diamond Shine & Sparkle?

Shine on You Crazy Diamond crooned David Jon Gilmour of Pink Floyd in the 1975 released album Wish You Were Here.

Well if you really want to know why diamonds do shine and sparkle, the reasons aren’t crazy if you love science that is.

At the outset let us understand that a diamond does not shine; rather, it reflects light, imparting an exquisite glitter to the diamond. Additionally diamonds are skillfully cut and polished to accentuate their inherent brilliance.

The Science behind a shining diamond

Total internal reflection

Diamonds shine and glitter due to their entire internal reflection. Total internal reflection happens at the border between two media when the incidence angle in the first medium is larger than the critical angle. If the incident angle in the first medium is higher than the critical angle, then all light is reflected into that medium.

There are 3 other factors apart from total internal reflection that contribute to the brilliance of diamonds: 

Reflection

Refraction & Dispersion

Reflection

When a light beam strikes a diamond and bounces back, it produces an immediate shine. The term "reflection" refers to light that strikes a diamond and is quickly reflected back up, imparting an instantaneous sparkle. While this gleam is stunning, it merely scratches the surface of a diamond's real brightness. A diamond reflects just a part of the light that strikes it; the remainder passes through it.

Refraction & Dispersion

 As light passes through the diamond, it is dispersed and broken, resulting in the diamond's renowned glitter. This is referred to as refraction. Diamonds are essentially small, intricate prisms; light enters at the top and is directed around the interior of the diamond before returning to the top and exiting through the surface. This results in a rainbow effect (dispersion) that enhances the brilliance. Additionally this refraction and dispersion result in natural bright and dark patches in the refracted light, depending on where the light strikes the diamond's planes. While these dark patches in the shine may seem to be counter-productive, they are really necessary for the diamond's hallmark brilliance to be achieved. 

Factors that can affect the shine of a diamond

Background where it is placed

A diamond devoid of contrast may still sparkle brightly, but the brilliance would be greatly diminished. It would be devoid of the radiance that diamonds need to sparkle.

The Cut 

The cut of the diamond also influences the brilliance of a diamond. If the form is too deep or too shallow, most of the light will be lost and never refract properly. The angle of refraction would allow light to escape through the diamond's bottom. That is why you have master diamond cutters who are entrusted with the job of cutting a diamond.

The Shape 

The diamond's shape also affects its brightness to some extent. Today's most popular forms have been optimized for light performance. These are the cuts that improve the brightness of a diamond by using the diamond's inherent qualities and intricate angles to achieve not only the maximum sparkle, but also to ensure that the diamond's real form is visually acceptable. 

Symmetry 

One of the most critical components of a diamond's maximum brilliance is symmetry, which is determined by the way the diamond is cut and fashioned. The diamond must be perfectly balanced on all sides, with all of the facets cut precisely. If the symmetry is even slightly incorrect, the light will not refract properly. 

Clarity 

The clarity of the diamond also has an effect on the brilliance, but to a lesser amount. Blemishes on the diamond's surface restrict the quantity of light that may penetrate. Inclusions obstruct the passage of light inside the diamond. These defects act similarly to stop signs and speed bumps; they alter the path of light. Fewer flaws result in a more brilliant diamond, since nothing (or almost nothing) detracts from the brilliance and glitter. 

Polish 

After the diamond has been precisely cut and fashioned to exactly reflect light, it is meticulously polished to its ultimate degree of brightness. Polishing has a long-lasting effect on the brightness of the diamond. Any remaining roughness or imperfections on the outside are very softly worn away. Diamonds are similar to nearly everything else in this regard; a thorough polish can really bring out their brightness.

It's not simple to make a diamond dazzle and shine perfectly; skilled specialists must understand precisely how to cut and polish each stone to get the greatest results.