The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Collographic Process
Process, but as this method is now scarcely used excepting in connection with negatives for photomechanical processes, the details given are hardly sufficient to serve as a complete guide to a beginner; and a clue to the various sources of failure - a modern handbook of the Wet Collodion Process - is Mr. Charles W. Gamble's " Wet Collodion Photography," published by Hazell, Watson & Viney, Ld. The older Dry Collodion methods may be dismissed in a few words. The plate as taken from the bath was washed to remove free nitrate of silver, and an organic liquid, as coffee, tannin solution, albumen, weak gelatine or gum was poured on, so as to prevent the collodion film becoming horny and impermeable on drying. Such plates may v-be preserved indefinitely under favourable conditions. Previously to development the plate was soaked in water to soften the film, and then development was performed with a wet collodion developer (see Wet Collodion Process), to which nitrate of silver had been added to replace that washed out of the film. The development of dry collodion plates with an alkaline developer and no free nitrate of silver, also the making of collodion emulsions by adding a silver solution to the collodion, were important steps in a long chain of experi-mental work which led to the evolution of the modern gelatine emulsion process. (See Emulsion.)
Collographic Process. Syn. with Collotype.
Collotype. Synonyms : Albertype, Artotype, Phototype, Lichtdruck. Collotype is a photomechanical process by which prints in greasy ink are obtained by means of a film of gelatine used as a printing surface. Briefly the process is summed up as follows: a film of gelatine containing a bichromate salt is exposed to light under a negative, washed, and inked with greasy ink, which adheres only to those places which have been affected by light. By using a suitable press many proofs can be obtained. Negatives for preparing the collotype plates, as they are called, must be reversed (see Reversed Negatives), and should be of a rather soft, delicate character, free from yellow stain. They should also be provided with a safe edge which is usually made of tin foil. It is customary to prepare several negatives of one subject when a large number of pulls or prints is required; as many as two, four, six, or eight,