Latent Developments from Gallic Acid, 1839

Abstract

With his fourteenth preparation of photosensitive material probably made in the first week of February 1839, John Herschel introduced gallic acid into photographic science. His “hopes of the gallate of silver” were communicated to W. H. F. Talbot in a letter of 28 February and indirectly through J. B. Reade towards the end of March ]839. Gallic acid was mentioned at the reading of Herschel’s paper on photography at the Royal Society on 14 March 1839, and the “somewhat problematic” light-sensitive combination of gallic acid with silver nitrate published by Herschel early in 1840. Unpublished photographic use of gallic acid by J. B. Reade in late March 1839, and brief published references to the chemical by A. Smee and G. P. A. Petzholdt during 1839 had little significance. Talbot purchased gallic acid on 30 March 1839, tested it six days later, and in 1841 patented the calotype technique in which gallic acid acted as a physical developer. Chemical ideas relevant in 1839 to the pre-developer use of gallic acid are discussed.