The method of development which we have detailed is as simple as any, and will be found suitable to any plates in the market. Its fault, if it have one, is that the pyrogallic acid is used dry, and being of a light woolly nature, it is apt to fly about, and contaminate other things in the room. Mixed with water alone it will only keep good for a few hours. If a good batch of plates have to be developed, it is the best plan perhaps to mix up the whole quantity of pyrogallic acid needed, and to measure off so much for each plate. Here is an alternative method of working by which the contents of a one ounce bottle of pyrogallic acid can at once be made into a solution which will keep good for months. In 8 ounces of water put 20 drops of nitric acid, and pour the mixture upon 1 ounce of pyrogallic acid. Eight drops of this stock solution will then contain I grain of pyrogallic, so that a developer can be quickly made up from it.
Hitherto we have considered only the case of a plate which has received the proper amount of exposure in the camera. With such a plate all is plain sailing. It developes itself as it were, and requires little attention beyond watching to see when the action must be stopped. But in the hands of a beginner, plates do not behave at first in this convenient manner. They are either under or over exposed, and the photographic aspirant is at first quite at a loss to know which error of these two he has committed. We will endeavour to enlighten him. An under exposed plate may be looked for after exposure in dull weather, or when the camera has been used late in the afternoon, when the sun has lost much of its power. If one plate out of a batch taken at the same time, and under the same conditions, turns out to be under-exposed; let the other plates be allowed to rest for three weeks or a month before they are developed. Strange as it may seem, there is a kind of continuing action of the light on a plate which has been once exposed, although that plate be subsequently kept in darkness. This continuing action will cause an under-exposed plate to ripen, so that eventually, after a rest like that suggested, it will yield a good negative.
"But how," it may be asked, "is a beginner to know whether a plate has been under-exposed." Simply by its behaviour under development. The sky will come out very slowly, and very little else wail appear. Dose after dose of "accelerator" may be added to the plate, but nothing seems to hasten it. If washed and fixed, it will consist of nothing but black sky and clear glass. Of course this is an extreme case. Under-exposure generally may be detected by the slowness with which the image makes its appearance, and the hardness of the contrasts between the lights and the shadows of the picture. There is no remedy for this state of things. The best thing to do under the circumstances, is to scratch the film across with the finger-nail, in case the operator should be afterwards tempted to print from such a production.
Over exposure is a more common fault, and this is fortunate, for the fault can be remedied to a great extent during the developing operation. Over-exposure is evidenced by the image flashing out on all parts or the plate at the same instant. The plate darkens all at once, and will speedily become one black mass unless a remedy be applied. Should this sudden flashing out of the picture occur, at once throw off the developer, and flood the plate with water from the tap. Now mix up some fresh developer, containing only one-third of the usual quantity of ammonia solution, and with a few drops of a ten per cent. solution of bromide of potassium added. This salt has a restraining action, as will be very soon apparent. A bottle containing it should be kept for such emergencies, and should be compounded thus: -
Bromide of potassium, ½ ounce. Water . . .5 ounces.
By such precautions an over-exposed plate may be developed into a decent negative. But let it always be remembered that nothing is equal to a properly exposed plate. An over-exposed one will generally require intensifying, a process that will be described later on.
Many other alkalies besides ammonia are used with pyrogallic acid as a developer, and although ammonia is most commonly used, the idea is gaining ground that it can be usefully supplanted by some of the others. It has the disadvantage of causing a plate to be discoloured if more than a certain quantity be used, which is commonly the case if the development be at all forced when under-exposure is being corrected. The two alkalies most often used in place of ammonia, are the carbonate of soda, and the carbonate of potash. We will first of all describe a very good developer compounded with carbonate of soda, i.e. common washing soda, not the bi-carbonate, which is often miscalled carbonate of soda. In a quart bottle, put washing soda ¼ lb., and fill up with warm water. Add 12 grains of bromide of potassium. For use take pyrogallic acid as before, pour upon it one ounce of water, and one ounce of the soda solution. Here we have a developer which yields first-class results. It has no smell, and the soda being a stable salt, a large quantity of solution can be mixed at once, for it keeps well. As in the case of ammonia, the alkali acts as an accelerator, and it must be diminished or increased as circumstances require. Carbonate of potash has lately come into extreme favour under he name of Beach's developer; for the popular way of using it must be attributed to Mr. Beach, of New York. The following method of making the developer has lately been published in several photographic periodicals, and it gives, when so compounded, the very best results.
Make two solutions: -
Warm Water ... ... 2 ounces
Sulphite Soda ... ... 2 ounces
When cold add
Sulphurous Acid ... ... 2 ounces
Pyrogallic Acid ... ... ½ ounce
A Water ... ... ... 4 ounces
Carbonate Potash... ... 3 ounces
B Warm Water ... ... 3 ounces
Sulphite Soda ... ... 2 ounces
Combine A and B. These two solutions keep well.
To develope, add to each ounce of water, 1 dram of No. 1 Solution, and ¾ dram of No. 2 Solution. This is weaker than Mr. Beach's formula, and it is best to commence developing with a still further dilution from two-thirds as strong, to even one-third, if overexposure be suspected beforehand.