[CHAPTER VI.]
LANDSCAPE PHOTOGRAPHY ON PRESERVED COLLODION AND COLLODIO-ALBUMEN.
The Collodion process may be applied with success to landscape Photography; but as the plates become dry and lose their sensitiveness shortly after their removal from the Bath, the operator will require to provide himself with a yellow tent or some portable vehicle in which the operations of sensitizing and developing can be conducted. As it is a point of great importance in the Collodion process that the plate should receive exactly the right amount of exposure in the Camera,—a few seconds more or less sufficing to affect the character of the picture,—many will submit to much trouble and inconvenience in order to have the apparatus complete upon the spot at which the view is taken.
The object of the "Collodion Preservative Processes" is to maintain the sensitiveness of the film for a certain length of time after it has been excited in the Bath. There is some difficulty in doing this, because if the plate be allowed to dry spontaneously, the solution of free Nitrate of Silver upon the surface, becoming concentrated by evaporation, eats away the Iodide of Silver, and produces transparent spots.
Some operators have attempted to use a second plate of glass in such a way as to enclose the sensitive film with an intervening stratum of liquid. The difficulty however of separating the glasses again without tearing the film, is considerable.
In the process of Messrs. Spiller and Crookes, the property possessed by certain saline substances of remaining for a long time in a moist condition was turned to account. Such salts are termed "deliquescent," and many of them have so great an attraction for water that they absorb it eagerly from the air: the solution having been formed, the water cannot entirely be driven off except by the application of a considerable heat.
More recently, Honey has been employed by Mr. Shadbolt.[52] This substance can scarcely be termed deliquescent, but it possesses, like other uncrystallizable sugars, the property of remaining moist and sticky for a long time. Honey is, according to the Author's views, superior to inorganic deliquescent salts as a preservative agent, from its possessing an affinity for Oxides of Silver, and thus acting chemically in communicating organic intensity to the image.—Collodion plates when kept long in a moist and sensitive state often give a pale and blue image, even although the Nitrate of Silver be left upon the film; and neither Nitrate of Magnesia nor Glycerine appears capable of supplying the deficient element, both being nearly or quite indifferent to the Salts of Silver.
[52] A claim has lately been advanced by Mr. Maxwell Lyte to be considered as the discoverer of the Honey Process. This gentleman appears to have worked simultaneously with Mr. Shadbolt, and to have anticipated him in publishing; but the object of Mr. Lyte's process was rather to increase the sensibility of the plates than to confer upon them keeping qualities.
THE HONEY AND OXYMEL KEEPING PROCESSES.