The Daguerreotype and Development of the Latent Image: “Une Analogie Remarquable”

Abstract

Immediately after the secret of L. J. M. Daguerre’s technique had been revealed in August 1839, the concept of an image “invisible et seulement latente” was clearly recognized. In a Paris nexvspaper Le Constitutionnel on 21 August 1839 a simple chemical comparison was made with widely familiar methods for revealing secret writing: “one sees the writing legibly stand out, the characters becoming as visible as if ink was formed there from nutgalls. That is exactly how Daguerre's images become visible as soon as the mercurial vapours come in contact. There exists between these two results a remarkable analogy”. The relevance of this analogy made in 1839 is discussed with regard to nutgall gallic acid being the prototype developer of the latent image in photography established through the calotype technique of 1841.