A Wratten number is a code used to identify photographic color filters. The system is named after Frederick Wratten (1840-1926), an English maker of photographic materials. His company, Wratten and Wainwright, was bought by Kodak in 1912, and Kodak continued the filter system.
Each color has its own number. For example, 25 is red, 21 is orange and 85 is an amber filter for color balance. Some numbers carry letters that show strength. The 81 series of pale warming filters runs from 81A, the weakest, to stronger ones such as 81B, 81C and 81EF.
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