Publisher's Synopsis
Excerpt from Photographic Reproduction Processes: A Practical Treatise of the Photo-Impressions Without Silver Salts; For the Use of Photographers, Architects, Engineers, Draughtsmen, and Wood and Metal Engravers
The varieties of cyanotype processes seem to be innumerable, but that which I shall now describe deserves particular notice not only for its pre-eminent beauty while in progress, but as illustrating the peculiar power of the ammoniacal and other parsalts of iron above-mentioned to receive a latent picture susceptible of development by a great variety of stimuli. This process consists in simply passing over the ammonio-citrated paper on which such a latent picture has been impressed, very sparingly and evenly, a wash of the solution of the common yellow ferrocyanate (prussiate) of potash. The latent picture, if not so faint as to be quite invisible (and for this purpose it should not be so), is negative. As soon as the liquid is applied, which cannot be in too thin a film, the negative picture vanishes, and by very slow degrees is replaced by a positive one of a violet blue color on a greenish yellow ground, which at a certain moment possesses a high degree of sharpness and Singular beauty and delicacy of tint. If at this instant it be thrown into water, it passes immediately to a Prussian blue. Losing, at the same time, however, .much of its Sharpness, and sometimes indeed becoming quite blotty and confused.
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