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The Firescope
The Firescope is a light-mapping instrument invented by a Tokyo diamond dealer in 1984. It uses simple colorcoding to show whether - or how - a diamond is leaking light.
The Firescope looks unassuming: a small metal box with an eyepiece. But the mechanism is extraordinary. A diamond is slid between a light source, below, and the eyepiece, above. There are red reflectors in the eyepiece. Any light reflecting through the crown and table is reflected back - but in red.
Red light means light reflection, but white light - which can't have reached the reflector - means light leakage. The amount of red and white light indicate a diamond's potential brilliance and the quality of its cut. A diamond with no light leakage will present an image without any white.
The Firescope was first introduced as an observation tool to help jewelers buy the most beautiful diamonds. What the instrument showed repeatedly, however, was that almost all diamonds leaked light, often badly. Even the Ideals.
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