Making The Solutions - Chemical Actions - Bringing Out And Fixing The Image

After a plate has been exposed it should be taken to the dark-room for development. Before describing this operation the developing solutions shall be explained.

The Developing Solutions

Consist essentially of two parts - "The Reducer" and "The Accelerator." The reducer will not develop a plate without assistance, the excitant is the accelerator. Unless, however, a third element be introduced, the action of the air and other oxidizing bodies would be so great that the solutions would quickly spoil and the plate would become stained; therefore, a preservative is used - this is generally dissolved with the reducer. Further, it sometimes becomes necessary to slow down or restrain the activity of the solution. This is effected by the addition of another chemical called the "Re-strainer."

The plate makers invariably publish instructions for making developing solutions suited to their plates. The most practical thing for the worker to do is to get a clear understanding of the nature of the chemicals and their actions, as it will be found that a slight variation in the proportion of the active ingredients of the developing solution will not appreciably affect their actions on the various makes of plates. A good plan is to practically ascertain the best working strengths of the active ingredients in grains per ounce of a solution. The solution may then be made up ready for use, or may be concentrated and diluted as required. In this way the working of any recipe may be reduced to utter simplicity. To give an example of how to reduce a recipe to grains per ounce, an ordinary hydroquinone developing solution will be taken as a model. It is always advisable, if the solutions are to be made up and kept for any length of time, to make them in two portions; the reducer and preservative in one, the accelerator and restrainer in the other, and call them either A and B solutions or Nos. 1 and 2, and mix as required.

Solution A

Hydroquinone . . 80 grs. Sodium sulphite. . 160 ,, Water .........10 ozs.

Solution B

Caustic soda .... 40 grs. Potass, bromide. . 20 ,, Water .......... 10 ozs.

To reduce this merely requires the amounts dividing by 10, or remove the nought, and we get: -

Solution A

Hydroquinone..... 8 grs.

Soda sulphite ..... 16 „

Water ........... 1 oz.

Solution B

Soda caustic ...... 4 grs.

Potass, bromide.... 2 ,, Water............ 1 oz.

We must not, however, stop here, because when working with the solutions we use equal parts of A and B, and one ounce of such mixture would be made up of half-ounce of each of the two. So that we should express our working formula as: -

Hydroquinone ................. 4 grains.

Soda sulphite .................. 8 ,,

Potass. caustic.................. 2 ,,

Potass, bromide 1 gram in each oz. of solution.

The construction of this formula is: hydroquinone, the reducing agent; sodium sulphite acts in the double capacity of preservative for the solution by retarding oxidation, and also prevents staining of the film during development; caustic soda is the accelerator; and bromide of potassium the restrainer. The tendency of the reducer is to give density, representing contrast and brilliancy, and the accelerator to keep it back, thus lowering the contrast and inclining to flatness.