There are a thousand and one formulas for developing solutions for the wet plate, but they are all composed of protosulphate of iron or a compound thereof, acetic acid, and water, with the addition of some organic substance, such as sugar, rock candy, glycerine, etc. etc.
The development of a negative is nothing more than the deposition of metallic silver in a state of fine subdivision upon a base of the same metal, which is the image latent in the collodion film after exposure in the camera. And it is supposed that the finer the deposit secured in the development the better will be the chemical effect and printing quality of the resulting negative. Therefore, the use of organic bodies in the developer is supposed to effect or induce a finer deposit. The careful observer, however, will soon discover that the success of the development depends more on the time of exposure, the temperature of the delevoping solution and the condition of the bath, than upon any adventitious aids, such as rock candy, etc.
A developing solution, composed alone of an aqueous solution of protosulphate of iron and acetic acid, can be made to produce the finest effects possible to the process.
Half fill with protosulphate of iron a wide mouth 64 oz. bottle, fill up full with water, set aside to dissolve, shaking the bottle once in awhile, so that the water may become saturated. Put a small glass funnel on a stand, so that you can place under it a 16 oz. bottle; fill the 16 oz. bottle with water and enough of the strong iron solution to make a twenty grain to the ounce solution, add one ounce of acetic acid, pour all into the filter and place the bottle beneath the funnel to receive it. This filtered solution is the developer for negatives.
Some experience is necessary to enable one to de-velope a negative properly and secure the best results.
Holding the plate in the left hand, take the developer bottle in the right, hold it over the plate near the left hand, let the first finger of the right hand rest against the edge of the plate, tilt the bottle so that the developer will run on the plate; at the same time move the right hand toward the other end of the plate rather quickly, letting the developer run in a steady, but not copious stream; deflect the plate with the left hand at the same time, so that the solution will flow from you in such a manner that the whole surface of the plate may be covered with the liquid at nearly the same time as possible. Now set down the bottle and keep the plate in motion, so as to cause the solution to have an equal action on every part of the surface. Very soon the image will appear and brighten, until every part of the detail comes out, and when it begins to look as if fading away or becoming less distinct the development is finished.
This can be ascertained with more certainty at this time by holding the plate so as to be able to look through it toward the light, so as to examine its density, remembering that the high lights should be quite dense and the medium shadows be full of detail. One very soon learns to know the proper density.
The plate should be now very thoroughly washed, to free the surface from the iron before fixing.
Great care should be taken in this manipulation to cover the plate quickly with the solution, holding it all on the plate. As the development is made by the precipitation of the free silver on the surface of the film upon the latent image, none of the free silver should be washed from the plate by a flood of developing solution carrying it off the surface.
Hyposulphite of soda is generally considered to be the most suitable fixing agent for negatives, although some prefer cyanide of potassium.
The hyposulphite, however, is the safest, both for the plate and for the operator. One pound of hyposulphite of soda to a gallon of water will make a solution of a suitable strength to clear a negative as rapidly as is necessary, and it should be contained in a flat dish. When from much use the fixing solution becomes muddy, it should be thrown into a suitable receptacle for liquid wastes, as it is rich in silver.
Leave the negative in the fixing solution until all the iodide of silver is dissolved from the film, and no trace of the yellowish deposit can be seen by transmitted light.
When the negative is thoroughly cleared, if it is found that it lacks density or, in other words, is not intense enough, wash it very carefully to free it from every trace of the soda solution, and then proceed to strengthen it in the following manner:
Keep near at hand in a 64 oz. bottle this solution:
Protosulphate of iron................... 2 oz.
Citric acid............................ 1 "
Water...............................64 " and in a small bottle a ten-grain-to-the-ounce solution of silver nitrate.
When a negative is to be strengthened, from the large bottle take enough of the solution to cover the surface; to this add a half dram of the silver and flow it over the negative.
A change of color will at once take place in the film, which will become darker as the silver deposit becomes heavier; if one application is not enough to secure the required density, wash the plate and proceed again, as before.
Negatives may be strengthened before fixing, if it is found necessary, by flowing the surface with the weak silver solution and afterwards using the ordinary developer.
When one has become accustomed to the work, and can tell that the negative is not dense enough before fixing, it is the best plan to re-develop before fixing.
Having described the positive and negative collodion process, there remains to give an account of the latest and greatest achievement in photographic progress.
The history of dry plate photography comes within the last ten or fifteen years, and being so recent and so fully written up in current photographic literature, space in this work will not be taken for a full account of the rise and progress abroad and at home of this wonderful improvement in photography, but instead will be given some formulae for the preparation of Gelatino Argentic Emulsion, and the most approved methods of working it.
The shortening of the time of exposure for sittings in the studio from one-tenth to one-twentieth of the time required for the old wet plate process, at its best, has rendered the dry plate such a power in the hands of the photographer as to have caused it to be almost universally adopted in the studios of this country, and has practically displaced the wet process in the field and for all out-door photography.