A Manual of the Collodion Photographic Process - The Development of the Image


Contents

Part 1

Part 2

PART III


The Development of the Image

The fourth division.–After exposure in the camera, nothing is visible on the glass. The image must be developed.


This operation is nothing more than making visible to the eye an exceedingly faint and delicate picture which the light, reflected through the lens, has impressed upon the surface of the film; it is, in fact, a continuation of the action of light, which action is the commencement of the reduction of the iodide of silver contained in the collodion, to the metallic state, carried on when thus commenced in the camera, by the reducing agent employed.


This effect is most apparent when a layer of albumen on glass is employed to- hold the chemical agents, when it very often presents more the effect of plating by mechanical means than the result of the apparently feeble action of a ray of light.


There are many chemical salts possessed of this power, of reducing the salts of silver when in solution to the metallic state.


The salts generally employed are pyrogal- lic acid, proto-nitrate and proto-sulphate of iron.


The great power shown by pyrogallic acid in bringing out the latent image, was first made known by me in a short description, in the May number of the “Chemist” for 1850. I then pointed out a mode of using if, so as to produce an exceedingly sensitive surface; in that formula, however, acetic acid was the solvent, both for the nitrate of silver and pyrogallic acid solutions. Even then its action was very energetic, requiring no after wash to bring out the image; it is also equally rapid when used in connexion with a surface of albumenized glass.


I will give the formula for pyrogallic acid; the other two agents named above may require a few words presently:

  • Pyrogallic acid ..... 3 gTs.
  • Water... 1oz
  • Acedic acid... 1 dr.

Mix the water and acetic acid first, then add the pyrogallic acid.


Take a small quantity of this solution in a porcelain cup or glass measure, kept expressly for the purpose, and pour it over the prepared glass immediately after removing it from the camera. This should be done with a quick motion of the hand, in order to. facilitate its spreading equally, and at once, over the whole surface of the glass. If-the plate should be very dry, after exposure in the camera, a slight immersion in the bath, before throwing on the developing liquid, will be of advantage.


The development must not be continued after the liquid floating on the glass has changed colour or deposited any sediment. The drawing would be injured if the action is continued thus far. If the image is not produced sufiiciently strong before this decomposition comes on, it may be considered an indication that the
exposure in the camera has been too short; and suggests its own remedy in the next trial.


The production of the image with the proto-nitrate of iron, can be conducted in the same manner as with the pyrogallic acid solution, taking care to add just sufficient acetic acid to the proto-nitrate to cause it to flow freely on the glass.


The proto-nitrate of iron, as prepared by the action of weak nitric acid on iron filings, is a good developing agent; but there is one difficulty attending it, which at times will be felt a serious bar to its use.


It is the impossibility, commercially speaking, of obtaining it as a crystallized salt; and being an easily decomposed solution, it would not be convenient to prepare by this means any large quantity at once, certainly not more than sufficient for a day or two’s consumption.


My own experience, resulting from some experiments recently made, is more favourable to the preparation of a solution in definite pro- portions of the two salts, the proto-nitrate and proto-sulphate of iron, than the use of either separately


Crystallized nitrate of baryta and proto-sulphate of iron are easily obtained, and a sufficient quantity of each can be carried with the other chemicals, when about to make an excursion of any length. The small quantity of the mixed solutions of proto-nitrate and sulphate of iron, required for immediate use, can be made just | previous to the commencement of operations.

Make a solution of nitrate of baryta 40 grs. to 1 oz. of water; when dissolved add to it 50 grs. of proto-sulphate of iron in powder; stir the mixture with a rod, and when the sulphate of iron is all dissolved, allow the precipitated sulphate of baryta to subside; when the liquid above becomes clear, it 1s ready for use. It is a solution of proto-nitrate of iron, with a small quantity of sulphate of iron. Add to every ounce of this about 1/2 a dr. of acetic acid.