Much of a diamond's brilliance and fire comes down to physics. In 1919, a mathematician used optical physics to calculate the optimal number and angle of facets to maximize the light captured and reflected by the gemstone.
Why Diamond Light is Beautiful
Published August 15, 2018
Narrator: Revealing a diamond’s beauty comes down to the careful arrangement of these facets.
Melvyn Kirtley: Diamonds need to be cut in very, very specific parameters to get it to maximize light return.
Narrator: This is the round brilliant cut, one of the most popular shapes in the world.
Kirtley: When a diamond is proportioned in a perfect way, it will act as a hall of mirrors. If it’s not, then the light will push out of the back and, you’ll basically lose light.
Narrator: In 1919, a Belgian mathematician named Marcel Tolkowsky used principles of optical physics and math to determine the optimum number and angle of facets to create a diamond that perfectly caught the light.
Kirtley: When he came along, it was more putting a science to the actual proportions and understanding that they matter.
Deborah Berebichez: Imagine this is an uncut crystal with a smooth surface on it, and now we’re going to shine green light onto it.
Narrator: Debbie Berebichez, a physicist, explains how light can be captured in a crystal, by using a green laser so our camera can see it.
Berebichez: So, we see that spot on the wall, because most of the light is getting transmitted to the other side. Now, if instead we use a faceted crystal, we can see how most of the light is getting trapped and bouncing around inside the crystal, and a lot of it is coming back reflected into our eyes, very much like a hall of mirrors.
Narrator: Tolkowsky found that a diamond cut with nearly 60 carefully angled facets created an exquisite geometry that reflected light around the stone many times, then bounced it out through the top and into our eyes. We call this phenomenon “brilliance.”
When white light enters a diamond at just the right angle, something extraordinary happens. These facets, along with how the diamond effects wavelengths of light, disperse it into a rainbow of colors, like light through a prism. This creates the flashes of color called “fire.”
Kirtley: Because of diamond’s hardness, the polishing of the facets creates such incredible mirrors that the diamond bounces the light back to the eye. So, you’re really getting a combination of light to give this beautiful dispersion and sparkle.
Narrator: It turns out that a diamond’s brilliant sparkle comes down to optical physics.
PRODUCTION CREDITS Digital Producer Arlo Perez Editorial Review Julia Cort, Ari Daniel © WGBH Educational Foundation 2018 MEDIA CREDITS Music APM