Influence of Pigments on the Photographic Image of the Spectrum

Abstract

WHEN, some time since, Prof. H. Vogel announced the discovery that the addition of a pigment to a film of bromide of silver made it sensitive to light of the colour which that pigment gave it, though it had not been so previously, many—indeed I might say most—photographic chemists doubted the accuracy of his observations and the existence of any such law. His experiments were rehearsed by most of them, and the reports were, in almost every case, contradictory of his conclusions. There were powerful à priori reasons for doubting, amongst which the chief was, in my own opinion, that if a film coloured (say) red were sensitive to red light, it could not be developed under red light, but would fog, and would therefore be unworkable, which was not found to be the case. Another was, that the use of tinted films, well known for a long time, had only resulted in an universal retardation of all colours. It was, moreover, contrary to the known analogies of actinism that a purely mechanical admixture irrespective of any chemical quality should produce changes of so purely chemical a nature as those which are the basis of photographic action.