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Colombian Emeralds

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Chelsea Filter

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The Chelsea filter is a common gemological instrument used to identify synthetic emeralds? from natural emeralds when intermixed in emerald batches. The device was originally conceived by Anderson and Payne in 1934 at the Gem Testing Laboratory of the London Chamber of Commerce in collaboration with gemology students at the Chelsea College of Science and Technology.

The filter works by transmitting wavelengths around both 690 nm and 570 nm that correspond with a the emission and absorption of natural emeralds. When a fine Colombian, Siberian, or an emerald from North Carolina is illuminated with a strong white light and then observing them through the filter, it will appear red, while other green gemstones will not. On the other hand some synthetic emeralds such as those of the Chatham, Linde, and Regency varieties are of such a profound red, that it is almost an immediate giveaway, and should make you immediately suspicious.

By contrast, emeralds from India and Africa will only be faintly red, or will not appear red at all. Brazilian emeralds may or may not appear red, depending on it's origin, and in some cases may appear more of a brownish-red.

Besides emeralds, the filter is also commonly used in conjunction with the identification of sapphires, aquamarine, green jadeite, and blue topaz.

When used in conjunction with other tools such as a dichroscope or jewelers loupe, assumptions about a materials identification can be made with a high degree of accuracy.

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