Chemical Background of Some Colour Masking Techniques

Abstract

Practical methods of colour masking developed by the authors in 1948-1958 are described. Reaction of unused colour coupler with diazotized amines and aldehyde-anils proved unattractive due to the need for exact control of the extra processing steps involved. Masking of the cyan dye image was accomplished by reaction with formaldehyde and colour developer followed by oxidation; masking of the magenta dye image was accomplished by the use of styryl dyes and aldehyde-bis-pyrozolone couplers followed by reaction with formaldehyde. The mechanism of these reactions is discussed in the light of chemical and photographic evidence.