A Manual Of Photography

CHAPTER VI. THE DAGUEBBEOTYPE. In the first division of this work, Chapter IV. page 35, all the details of the original processes are given with considerable minuteness, and the vignette heading to that section exhibits all the apparatus required for even the improved modern practice. Section I—Daguerre’s Impboved Manipulation. The following remarks by M. Daguerre on polishing and pre- paring the platos, from the Comptes Rendus of March 13, 1843, should be carefully attended to, as the preliminary process upon which the success of every subsequent state depends. “ Since the publication of my process, I have not been able to occupy myself much with it. The investigations to which I devoted myself have been in an entirely new direction, and the experiments which they required were analogous with the pre- ceding ones, only inasmuch as they were made on a metallic plate. However, I have lately been so much struck with the unequal results which the impressions generally present—even those of persons who are especially occupied with them—that I determined to seek some means of remedying this serious incon- venience, which I attribute to two principal causes. “ The first relates to the operation of polishing, which it is physically impossible to effect without leaving on the surface of the plate traces of the liquid and of the other substances used in this operation : the cotton alone which is employed, however clean it may be, is sufficient to leave a film of dirt on the silver. This first cause constitutes a very great obstacle to the success of the impression, because it retards the photogenic action by preventing the iodine from coming in direct contact with the silver. “ The second consists in the alterations of the temperature of the air with which the plate is in contact, from the first operations to the mercurial operations. It is known that when a cold body is surrounded with warmer air it condenses its moisture. To this effect must be attributed the difficulty which