Advanced Loose Diamond Buying Tips: Light Performance Edition

Most loose diamond buyers know about the basics of diamond shopping—the Four C’s, certification, etc. But for anyone who has already bought a loose diamond before, or is looking for a truly spectacular loose diamond for an engagement ring or another piece of jewelry, you may be ready for advanced diamond buying skills. These are the factors that professionals take into account when choosing loose diamonds to display and sell. This is the kind of insider information that separates the casual diamond browser from the serious diamond hunter.
solitaire engagement ring with round cut diamond four prong
Diamond Engagement Ring
The first thing you should acquaint yourself with is the Holloway Cut Advisor. Created in 2001 by Gary Holloway, the HCA caused quite a stir in the diamond industry when it first hit the scene. With the HCA, you can enter the proportions of a loose round diamonds that you are thinking about buying, and the HCA will give you a score that gives you a sense of how well the diamond will perform in real life.
We all know that the better quality a diamond is, the more it will sparkle, but did you know that there is so much more to light performance than just light reflection? There are many elements of light dispersion that only the really advanced loose diamond shopper knows about. Here are the most important factors:
Brilliance is an essential attribute of a beautiful diamond and has two components; brightness and contrast. Bright diamonds return lots of light from the surroundings back up to the observer. If light from above leaks out the back of a diamond, naturally it has less brightness. Diamonds that are too deep or very shallow do this and return less light and so they have less brightness.
But to be brilliant, a diamond needs more than just brightness from light return. Fire or dispersed light appears as flashes of rainbow colors. You see more fire in darker environments like restaurants that have just a few point light sources or a flickering candle.
Diamond experts have known for a long time that steep crown angles and small tables produce more fire. But this combination also produces less light return. Less light return makes it easier to see colorful flashes that might otherwise be swamped by bright white sparkles. That’s why some fancy shapes have more colorful fire than traditional round brilliant.
Scintillation is the sparkle you can see in a diamond as it moves. Black and white sparkles of scintillation show well in flood lit or office lighting environments where fire can be totally absent. Under pin point or spot lights fire also adds to scintillation. Ideally a diamond has many pleasing flashes spread across the surface of the stone.
Glare is light reflected off the diamonds surface. As a general rule about 20% of the light that falls on a diamond is likely to be returned to your eyes as reflection. This light will be of the same color as the source. Diamond has the highest reflectivity of all gemstones, partly because it has the highest refractive index (the two are related), and partly because diamond takes the best polish of all materials because it is so hard.
6 prong tiffany style diamond ring
6 Prong Solitaire Ring
The remaining 80% of light enters the diamond and reflects around inside the stone until it all comes out. The goal of diamond polishing is to position facets so that most of this 'refracted' light leaves via the table or the crown facets. A diamond acts like a hall of mirrors, taking the light via the 'windows' or facets on the top of the diamond, reflecting it from mirror like pavilion facets, back out the crown and table 'windows'. Light that leaves the back or out the pavilion of the diamond is called leakage.
The fish-eye is not a well-known loose diamond phenomenon, but skilled loose diamond hunters know how to look for and avoid the fish-eye. A fish-eye is a dull spot that you can see just inside the table of a diamond. The fish-eye is a reflection of the girdle (on the opposite side). If the girdle is not polished and is thick the effect looks like a BIG circular inclusion. The HCA discussed above takes the fish-eye effect into account when grading loose diamonds.

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