Anatomy of a diamond and the effects of light
The diamond structure
A diamond is made up of two key sections, the Crown and the Pavilion. Their structure and relationship to each other in the form of table and depth percentages have the biggest impact on the diamond’s sparkle.
The round brilliant cut has been used as an example, because with most other diamond shapes (“fancy cut” diamonds) the cut grading is more complicated (hence why their cut grading does not appear on certificates such as GIA).
Diameter: Width of the diamond at the widest point of the girdle (in fancy cut diamonds, the smallest diameter is used).
Table: The largest facet at the top
Crown: The top part of the diamond between the girdle and the table
Girdle: The narrow band at the diamond’s widest point
Pavilion: The bottom part of the diamond between the girdle and the culet
Culet: The fact at the bottom tip (preferable when not visible to the naked eye)
Depth: The height of a diamond from the table to the culet
The Effects of Light on a Diamond
The science behind a diamond's brilliance depends on its great ability to bend, slow and direct light as it passes through. The cut of a diamond determines how well the diamond is able to re-direct the light back through the surface of the diamond. Light travelling at about 186,000 miles per second, when passing through a diamond is reduced to about 77,000 miles per second, close to the maximum for any other transparent substance (another reason why we are 77 Diamonds).
A ray of light hits the diamond's surface. Some of the light enters, and part of the light reflects back. The immediate reflection is the light given off by the crown angles.
The remaining light enters the diamond and reflects toward the centre of the diamond. The light that bounces off the internal wall of the diamond is the refraction.
The ray of light then shoots to the surface through the top of the diamond. A colour spectrum is visible when light exits the diamond.