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Filter for gems-made by high quality optic glass
-color never fade ,no degumming
-frosting aluminium alloy crust
Gemstone color filter,Chelsea filter
- with high quality optic glass;
- excellent spectrlite color filter;fastness and non-lackness;
- frosting aluminum alloy crust,delicateness and top quality;
- black color and leather package.
It is important to recognize what a Chelsea Filter IS and more importantly, what it ISN'T.
Chelsea Filters are simply dichromatic filters developed in 1934, not originally intended to be used for gemological purposes.
The filter is only able to transmit light in 2 regions of the spectrum: deep red (690nm) and near yellow-green (570nm).
Therefore, an object can only appear red or green or a brownish tone, resulting from a combination of red and green, when viewed through the filter.
That is because many Colombian and Siberian emeralds absorbed most of the yellow-green portion of the spectrum, but NOT the red portion of the spectrum. Therefore, when viewed through an apparatus only allowing transmission of red or yellow-green, they appear red.
This characteristic is NOT true with all emeralds. Typically African emeralds and Indian emeralds absorb portions of the spectrum around 690nm, so they will NOT appear red when viewed through a Chelsea.
When one viewed green glass, green sapphire, many green tourmalines, etc through the filter, they did not appear red as these stones were absorbing red color around 690nm.
BUT there are varieties of green flourite, green zircon and demantoid garnets which also absorb the yellow-green portion of the spectrum while transmitting red.
With the development of synthetic emeralds in the mid to late 20th century, it was observed that ALL synthetics appeared red when viewed through a Chelsea, as they were colored solely by chromium, thus absorbing in the yellow-green and transmitting the red.
Well, more filters were developed to separate natural and synthetic emeralds.
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