VARIATIONS IN DEVELOPMENT.
The ferrous oxalate or iron developer is, however, by far the most popular on the Continent, and with some few photographers in this country, and certainly it has some advantages.
Were the negative, instead of the print, the end at which the photographer aims, certainly the iron devel oper would be the one to adopt. The colour of the image given by it is very much more pleasing to the eye than is the colour given by the alkaline developer. Moreover, the manipulations are cleaner. It is quite true that with ordinary care it is possible to work the alkaline developer without staining the hands, and it is also true that the stain even if made is not as indelible as a silver nitrate stain. The oxalate developer has, however, this advantage that it produces no stain at all.
The following chemicals are required for this de veloper : Sulphate of iron.
Oxalate of potash.
Bromide of ammonium.
Of the first two of these saturated solutions in water are made,—that is to say, as much of each of them is dissolved in water as it will take up.
This may be done in the following manner : A pound of protosulphate of iron is placed in a pint bottle. Over this is poured hot water almost to fill the bottle, and the whole is shaken till as much of the crystalline substance as will dissolve has done so. As the solution is used water may be added, the bottle being shaken each time that this is done.
The very same process is gone through with a pound of oxalate of potash.
It is quite true that this plan of using saturated solu tions is not a very accurate one, as the amount of the chemicals which remains dissolved varies with the tem perature. It appears, however, to be quite good enough for all practical purposes.
The solutions must, of course, not be used till they are cold.
The bromide of ammonium may be used in a ten per cent solution, as was described at the end of the last chapter.
We now have— No. 1. Saturated solution of protosulphate of iron. No. 2. Saturated solution of oxalate of potash.
No. 3. Ten per cent solution of bromide of ammo nium.
Nos. 2 and 3 will keep indefinitely. No. 1 will keep for a considerable time in a well-stoppered bottle, but not indefinitely. It should be of a bright green colour.
If it turns reddish it is a sign of deterioration.
Just before we commence development we take two ounces of No. 2 ; into this we pour half an ounce of No. 1; immediately the solution assumes a beautiful ruby-red colour, due to ferrous oxalate, which is formed.
Development is performed with this solution precisely as with the alkaline developer, but will, as a rule, be found to proceed more slowly. It is necessary also to make the apparent density of the negative somewhat greater than with the alkaline developer, as the colour of the film is less non-actinic. The time taken with most subjects will be about from three to five minutes.
It is not in most cases necessary to use any bromide of ammonium at all, unless the plate has been over exposed, when a little is added to the developer to re strain its action. Many operators, however, prefer to have a little bromide in the solution in all cases, as clearer shadows are thereby obtained ; but, as the re straining action of bromide is much more energetic in the case of the iron developer than is that of the alka line, a less quantity is sufficient. Not more than about two or three drops of the ten per cent solution should be added to each ounce of developer unless there has been decided over-exposure. Ten drops to the ounce is enough to compensate for very considerable excess of exposure.
With the oxalate developer there is no accelerator which can be used as ammonia is with the alkaline developer, but a slightly similar effect may be brought about by using a little hyposulphate of soda.
It is best to prepare a very weak solution of this. One containing five grains to the ounce of water is sufficient. A few drops of this added to the oxalate developer brings up somewhat more detail on a plate, but great care must be exerted or a reversed action will commence which will destroy the negative. More than twenty minims of the weak solution mentioned should never be added to each ounce of the developer.