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Optimum Optical Performance

This is a Mandatory Example: you will see it in some form in about every book that refers to faceted gemstones... it must be symbolic of some Greater Truth, or it wouldn't be in so many places!

For this example, think of looking down at a ring on your hand, in a typical room with one light on the ceiling: for the best optical performance, the light from above must be reflected back towards the viewer (you- looking from above). These images demonstrate the path of a ray of light as it travels into, through, and out of that faceted stone.

(Technically, in these computer renditions, the light reaching the viewer's eye is leaving the top of the stone on the left; on the right (or bottom) is where the light would have to come from to reach the viewer. There is only one light in this room, so rays coming in from the side will not look nearly so bright as the rays coming in from the light bulb itself, which is right over the stone.)

Stone Cut Too Shallow

Picture of Shallow-Cut stone w/poor light reflection This is a light ray bouncing through a shallow-cut stone; notice that the light is not being reflected back to the viewer... this results in a lack of brightness and "fire". This stone would appear "fisheyed"- dull and lifeless in the center. Much of the cutting done overseas demonstrates this effect.

Stone Cut to Ideal Proportions

ideal cut stone w/light ray bouncing back to the viewer. This is a stone with ideal proportions, notice that the bright light from above is being reflected back to the viewer- this stone will appear bright and "lively". An important part of what makes this cut ideal is that it is not "leaking" light out of the back and sides of the stone.

Stone Cut Too Deep

This stone is cut too deep, light ray exits through stone bottom. This stone is cut too deep for fine optical performance. Notice how the light ray travels right through the stone. This stone would be dark and/or lifeless, also.

The above images were created with RayWIN.

Brightness is not the only consideration in cutting any stone; but it's definitely a primary focus in most cases! Some cuts are designed to maximize dispersion, color, or various optical and physical properties of a stone. The above comments are still likely to apply to just about any stone: dull and lifeless stones are generally perceived as less beautiful/desirable.

Does proper cutting matter that much? If light from above is going out through the bottom, then light (or lack of) from the bottom is coming out through the top! Do you really want a window to see how dark the inside of your ring is?
Sure, foreign-cut stones often cost less! Now think about how often and how long we spend looking at the jewelry we wear, and decide if a little extra isn't worth the added enjoyment.

Here's the picture worth a thousand words:
Picture of a stone I have cut, and a foreign-cut stone.
They are both sky-blue topaz- I cut the one on the left; the one on the right was cut overseas.
Notice how the tabletop is visible through the center of the foreign-cut stone (a typical "fisheye")!

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Page maintained by John Franke, facet@gemcutter.com. Copyright(c) 1995-2015.
Updated: 10-10-06 All Rights Reserved.