The characteristic appearance of prints which have been I much sulphuretted in the toning Bath, and are very liable to fade, should be known. A yellow colour in the lights is a bad sign; and if the half-tones are at all faint and indistinct, with an aspect of commencing yellowness, it is almost certain that the Positive will not last for any considerable length of time.
[CHAPTER IX.]
ON THE THEORY OF THE DAGUERREOTYPE AND TALBOTYPE PROCESSES, ETC.
SECTION I.
The Daguerreotype.
It was not the original intention of the Author to include a description of the Daguerreotype Process within the limits of the present Work. The Daguerreotype is a branch of the Photographic Art so distinct from the others, that, in manipulatory details, it bears very little analogy to them; a slight sketch of the theory of the process may not however be unacceptable.
All necessary remarks will fall under three heads:—The preparation of the Daguerreotype film;—the means by which the latent image is developed;—and the strengthening of the image by Hyposulphite of Gold.