This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
864 Following closely on the heels of the earliest method of taking portrait photographs - that is, on a silver plate by the Daguerrean process - came the discovery of the use Of collodion as a transparent vehicle for holding the salts sensitive to light. The Daguerreotype had the disadvantage that the image was reversed (although a positive) and was not reproducible, so was speedily displaced by the newly discovered wet collodion process, which gave results equal in fineness and gradation to any produced by the modern dry plates. It was styled the wet plate process, because it had to be used in a wet, freshly-prepared condition to retain its sensitiveness. It was not until some time later that a dry sensitive collodion emulsion was devised, and this again was speedily displaced by the gelatin emulsion of the dry plate as we know it today.
865. The original method of the wet plate process was to flow a collodion film containing metallic iodides on a sheet of glass, and then to sensitize the film in a solution of nitrate of silver. This formed iodide of silver salts, which were more sensitive than nitrate of silver salts. The exposure was made while the plate was still wet from immersion in the silver bath, and then developed in a solution of pyrogallic and acetic acids, being subsequently fixed in hypo. This process is essentially the same as the wet plate process still in use.
Application Of Wet Plate Process. While the wet plate process is not a difficult one, yet for studio and general photographic work it has outgrown its usefulness. However, there are special departments of photography for which the wet plate is indispensable and is better adapted than its rival, the dry plate. For instance, for the photographing of large drawings, maps, etc., the wet plate gives the best results both on account of its greater economy when large plates are used and because clear lines and dense backgrounds can readily be obtained. This process is, therefore, principally employed by the government, where thousands of maps and drawings are to be reproduced, and in large commercial studios where similar work must be reproduced.
867. The wet plate process is also used for certain kinds of technical work, such as the making of negatives for process work for photo-engraving, etc. It is also used in making enlarged negatives, lantern-slides, and for microscopic work. For the latter mentioned purposes it has two distinct advantages over the modern dry plates - first, its cheapness, and second, the possibilities of obtaining greater density of deposit, together with the extreme clearness of shadows. Still another reason, more especially for microscopic and lantern-slide work, is the possibility of producing the extremely fine grain, which is an advantage where fine detail is required.
868. The manufacturers of the dry plate of today are endeavoring to imitate the qualities of the wet plate, and in many instances they have met with success; but, owing to the difference in expense between the two, the wet plate will always hold its own for commercial purposes.
869. In the early days of the wet plate process, the photographer was not only compelled to prepare his own collodion, but also the pyroxyline (gun-cotton) from which the collodion was made. Today, however, collodion can be purchased already prepared for use, and while large consumers of collodion prepare their own chemicals, yet the making of gun-cotton has been dispensed with and this product is bought ready for use from the supply dealers.