A Photographic beginner will be apt to imagine that if a plate has been exposed in the camera, that it will at once bear an image of the subject upon which it has been exposed, and he will probably be surprised when he is told that the plate bears exactly the same appearance after that operation which it did before. But all the same, a change has taken place, and an important change too, but as yet it is invisible. The plate now bears, what is commonly called, a latent image, but this image only becomes visible under the operation, called development.
There are several different methods by which a gelatine plate can be developed, but it is a safe rule to adopt the formula recommended by the makers of the particular plates used. It is the invariable custom for makers of plates to issue with them plain directions for their development, but as these instructions are necessarily brief, we will endeavour to explain in detail the various operations necessary. We will also give one or two different formulae which will be found to produce good negatives with most of the plates now sold.
First of all we will describe the method most commonly in vogue in this Country, and which is known as alkaline development. The chemicals required are the following, which should be purchased of some reliable dealer in photographic requisites:-
Liquor Ammonia ( 880),
Bromide of Potassium,
Hyposulphite of Soda.
It will be of some assistance to the beginner if we make one or two remarks with reference to these chemicals. Pyrogallic acid is a snow-white woolly powder, so light that a one ounce bottle of it would contain about twelve ounces of water. One ounce, costing about sixteen pence, is sufficient for developing many dozens of small pictures, for only about three grains are required for each plate, and the ounce contains 437 grains. This chemical is very poisonous, and it stains the fingers. But the fingers never need come into contact with it, if our directions are followed. A bone mustard spoon should be kept for the purpose of taking it out of its containing bottle.
Liquor Ammonia 880 is the strongest solution of Ammonia that can be purchased. It quickly loses strength by exposure to the air, indeed it is not too much to say that it loses strength every time the stopper is removed from the bottle. For this reason only a small quantity should be purchased at a time, just sufficient to make up the formula required. The heat of the hand on the bottle is quite enough to sett' ff Ammonia in the form of gas, and for this reason the stopper should always be tied down, except when in actual use. Some adopt the plan of mixing the Ammonia at once with its bulk of water, and allowing for the addition in making up formulae. But the best plan is to purchase just sufficient for present need.
Bromide of Potassium is in crystals, and is a stable compound. One ounce will be quite sufficient to begin with.
Alum (powdered). We recommend the reader to put a pound of it in a half gallon bottle, and to keep the bottle always full of water, adding water every time the bottle is drawn upon. This can be done until all the alum disappears from the bottom of the bottle, when more must be added. By this plan the water in the bottle will always be saturated, that is to say, it will contain as much alum in solution as it can hold Hyposulphite of Soda, which we will call hereafter "Hypo." for short, should be kept in a stone jar, in a dry place. While a most useful and indispensable salt in its proper place, it is a thing to be dreaded by the photographer should it get out of that place. Fingers which have touched "Hypo." must not touch plates, dishes, or anything else in the photographer's list until they have been well washed. The hypo dish must be used for hypo and nothing else. Indeed we may go further than this, and recommend that one particular dish should be used for each solution required.
The necessaries for developing beyond these chemicals comprise:-
A good supply of water,
Scales and weights,
A graduated glass measure,
A developing cup or glass. Dish. No. I is reserved for the developing solution, to be presently described. Dish No. 2, placed near it, is to cont. . a few ounces of the alum solution taken from the stock bottle. Dish No. 3 - which may conveniently be double the size of the others, so as to be distinctive, and to have the further advantage of containing two plates at the same time - is for the hypo solution - (hypo. 2½ ounces, water ½ pint). This dish, for the reason already given, may be placed at a respectful distance from the others. These dishes will then be placed on a table in front of the operator in the following order:-
We will now proceed to develope a plate, which we will suppose to have received the proper amount of exposure in the camera. Let us also suppose it to be a landscape subject, consisting of a liberal amount of sky, a few trees, and a foreground. Mix up the following solution, and place it in a small stoppered bottle, from which it can readily be poured drop by drop. It may be regarded as a stock solution, and will keep well if stoppered when not in use: -
Bromide of Potassium ... ... 2 drachms.
Water ... ... ... ... 4 ounces.
Liquor Ammonia ... ... 2 ounces.
Let this bottle be labelled with a large A which can easily be discerned in the dim light of the dark room. The A will stand for accelerator, for this solution has the property of quickening the action of the developer. On the label, too, may be written the formula of the solution. This is a most convenient custom, and should be observed with all bottles in the laboratory.