To six ounces of A, add one ounce of B; this order of mixing must be observed or a dense precipitate of ferrous oxalate will be formed.
Place one of the soaked prints face (which may be distinguished by its "slippery" surface) upwards in a clean porcelain dish and pour the developer over it as evenly as possible. With this developer, the image comes up very rapidly, so that it is not advisable to try and develop more than one at a time. If the first print of a batch appears to be over-exposed, that is, if it flashes out instantly and the high-lights become rapidly clouded, add to each ounce of mixed developer from 10 to 30 drops of a ten per cent. solution of potassium bromide which will act as a restrainer, retard development, and keep the high-lights clear while the shadows acquire density. Under-exposed prints can rarely be made to give passable results with ferrous oxalate. The addition of a trace of hypo to the developer has been recommended for bringing up their detail, but the result is far from good.
As soon as development is complete the prints must not be put in clean water, but must be transferred direct from the developer to the following acid bath:—
| Acetic acid | 1 | dram. |
| Water | 32 | ounces. |
After an immersion of one minute, the operation must be twice repeated in similar baths that have not been previously used; this is to remove the iron from the print. A thorough washing must next be given to remove the acid and the print may then be fixed for at least fifteen minutes in
| Hypo | 2 | ounces. |
| Water | 20 | ounces. |
After fixing (no matter what developer has been used) the prints must be thoroughly washed in several changes of water for at least two hours.
The chief reasons against the use of ferrous oxalate are lack of control over development and the necessary use of an acid bath. Unless the acid bath is used, the prints will be yellow because of the iron in them, and if the acid is not entirely removed before fixing the prints will be yellow owing to the decomposition of the hypo by the acid in the print which causes deposition of sulphur.
Metol Developer.—With this, and the other developers I shall mention, an acid bath is not necessary and so one cause of failure (and extra work) is obviated. I have somewhat amended the Barnet formula to meet the needs of workers on a small scale and have also arranged A and B to balance each other without disturbing the relative proportions of the ingredients.
| A. | ||
| Metol | 120 | grains. |
| Water (cold) | 24 | ounces. |