Why Do Diamonds Sparkle? January 13, 2017 – Posted in: Jewelry Blog

Diamonds sparkle. It is for this reason, and many more that they are so popular in jewelry, and particularly in engagement rings. But why? What makes them sparkle?

Crystal glass, even of the highest quality, will never compare to the best diamonds, despite being absolutely colorless and flawless. So why should a diamond twinkle and shine like a star in the night sky?

The Science Of Diamonds and Refraction

Emerald Cut Diamond Sparkling in light

Without getting into the technicalities, the light properties of diamonds are actually pretty unusual among the common gemstones used for jewelry.

The two most important aspects of a diamond that allows it to sparkle are:

  • The cut
  • The natural properties of the diamond itself

Pure diamonds are made up of carbon, the element that gives life to us and everything around us. It is the unique structure of the carbon atoms in a diamond that gives it highly refractive properties.

This high rate of refraction (about 75% higher than glass) means that much less light is reflected from the surface. Much of the light goes on to be bounced around the diamond internally before exiting. This effect adds considerable life to the light that eventually comes back to the eye.

The process of reflecting back more of the light after refraction is known as Total Internal Reflection. This is as opposed to simple reflection such as in light hitting a mirror. Refraction isn’t unique to diamonds. Diamonds, however, do have a much higher Refractive Index (RI) than the likes of sapphires, emeralds, and other precious stones. In fact, a diamond’s RI of 2.4 is second among all gemstones, and you have to go all the way down to 1.7 before the like of rubies and sapphires make an appearance. Here is a link for a complete list the refraction index.

Consider that opals are the least refractive of all gemstones with an RI of 1.37. It’s easy to see that diamonds are a little bit special. It is no surprise that diamonds dominate the manufacture of engagement rings.

The Diamond Cut and Sparkle

Cushion Cut DiamondUncut, rough diamonds have exactly the same refractive properties as a cut and polished diamond, and yet they don’t sparkle like the finished item. This is because expert gem cutters have perfected the art of cutting diamonds. They use careful planning to ensure that as much light as possible is reflected back out of the stone. The light needs to come out in the same direction as it entered.

The angle of the pavilion is the crucial element that determines how much light is reflected out of the diamond. In a pavilion at the perfect angle and with the perfect proportions, light entering the top of the diamond is reflected across the pavilion and then back up out of the top of the stone. This light will appear to sparkle as you move the diamond.

In deeper pavilions, some light will be lost out of the side and bottom of the diamond after the first reflection. In shallow pavilions, a lot of light travels straight through the diamond and out of the bottom.

The skill of the craftsman cutting the diamond, along with the planned design is crucial to how much sparkle a diamond emits. It shouldn’t be underestimated. When a well cut, high-quality diamond is seen, the effect on the viewer is often one of wonderment. Such is the level of light reflection after it has been bounced around the diamond.

Light is a remarkable, living thing, and diamonds are the perfect delivery method for it.

Click here to view the Estate Diamond Jewelry Collection of vintage diamond engagement rings.