DEVELOPING This article will be devoted to a simple ex planation of the ordinary method and practice of developing a dry plate. The exposure having been made, the closed dark-slide is removed to the dark-room, and the plate developed either at once or at any convenient time afterwards. The work must be done in a safe light. In front of the lamp place a cleaned earthenware developing dish of the required size, and near it a glass measure containing about 2 oz. of the developer. Into another dish pour some fixing solution, made by dissolving 4 oz. of sodium hyposulphite (" hypo ") in 20 oz. of water.
As all photographic solutions work more slowly when cold, it is advisable to mix up all solutions some time before they are needed, as when freshly mixed they are very cold, particu larly the " hypo " solution, which drops almost to freezing point when newly mixed. By stand ing some time, the solutions become of the same temperature as the room. Anything between 65° and 7o° P. (18° and 21° C.) is the best for developing and fixing solutions.
The beginner is recommended to use the hydro quinone-metol developer (see " Developers, Mixed "), and he should be informed that each chemical in the formula plays its own part. Hydroquinone and metol are the developers proper ; but they need the help of the other ingredients. Hydroquinone gives density, and metol detail ; so by combining the two, density and detail are obtained at the same time. The sodium sulphite is included to preserve the solu tion, and is called the preservative. The sodium carbonate or potassium carbonate quickens the developing action, and is called the accelerator. Potassium bromide is frequently added, and this controls the action, and keeps the negative clear. As each has its own characteristic action, it will be obvious that were the chemicals in separate solutions, they could be so adapted, if necessary, to suit under- or over-exposure ; but there is no need to trouble with separate solu tions. A good mixture is given below : Hydroquinone . . 3o grs. 7 g.
Metol . . . to „ 2.3 „ Sodium sulphite . 35o „ 8o „ Sodium carbonate . 35o „ 8o „ Potassium bromide 5 ,, ,, Water to . . . 10 oz. i,000 ccs.
Take particular care that no stray light enters the room, and that the only illumination comes from the red lamp. Remove the exposed plate from the slide and look at it, but not too near the lamp. Nothing on it will be seen ; it will appear exactly as it did before the exposure. The image is latent (that is, concealed or hidden), and it needs to be brought out by the developer. Put the plate in the developing dish, the sensitive or creamy side of the plate being upwards and the glass side resting on the bottom of the dish. Then pour the developer over the plate in one quick sweep, so that the plate is completely covered in one sharp even flow, preferably from one corner. If the developer is properly applied, no air bubbles will form ; but should any appear, break them quickly by touch ing them gently with the finger-tip, or, prefer ably, with a clean camel-hair brush. Then rock the dish from side to side and end to end, so that the developer flows evenly over the entire plate, taking care to expose it to the red light as little as possible. The brightest parts of the resultant picture, such as the sky, white collars, and white dresses, etc., will appear first of all. If the expo sure is a landscape the sky will be the first to appear ; but it will be black, as all lights and shades are reversed in a negative, the black or very dark parts of the actual scene appearing as almost clear glass and the whites almost or quite opaque. After the sky, the half-tones of the pictures will appear, and finally the details in the shadows. The developing dish must be gently rocked all the time. When the image has appeared, the plate must not be removed, but development continued for some little time longer, so as to add density to the negative. Continue for about a minute or so after the density appears to be correct, as this will be considerably reduced in the fixing bath.