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plate, developer, solution, image, pyro, quantity, dish and water

DEVELOPING TUBES.—Glass tubes with closed ends, one containing pyro and the other ammonia. They are made for the convenience of tourists. iArhen required for use the ends are broken off and the solutions mixed with the proper quantities of water.

DEVELOPMENT.—The process of rendering the latent image visible by means of a suita ble agent. Under developer we have a large quantity of formulae, and we have under this heading to describe the method of applying to the exposed plate.

Before proceeding to develop it is almost essential that the operator should have some knowledge of the plate about to be developed. If he has himself made the exposure he will generally be able to tell whether the error in exposing, if there is likely to be one, will be in under or over exposure. For this he will be guided principally by the subject itself. The developer is then mixed up accordingly. In all developers we have an accelerator and a retarder, and the careful and judicious arrangement of these solutions is one of the secrets of success in development.

It must not, however, be imagined that a short exposure in the camera can be righted by prolonged development. There is a certain time necessary for the formation of the invisible image, which can only be shortened or lengthened to a very limited extent. With the pyrogallic acid developer more latitude is allowed; with ferrous oxalate very little.

The exposed plate in the dark slide is removed to the dark room, and there it remains until the developing solutions have been made up and are perfectly ready. With each make of plate is usually given the formula for development most suitable, and as this is usually the result of careful investigation of the various formulae it should be carried out wherever possible.

The following method of developing with pyro and ammonia serves well with almost every kind of dry plate: Take about four grains of dry pyro and zi ounces of water. This quantity is sufficient for a half-plate; for larger sizes multiply propor tionately. Dissolve the pyro in the water, place the exposed plate in the developing dish, and flow the solution over it. To the pyro should be added a small quantity of a restrainer.

With a soft camel-hair brush then remove all air-bubbles or foreign matter from the surface of the film. Into a clean measure next place about two drachms of a ten per cent.

aqueous solution of ammonia, and pour into this the pyro solution from the developing dish. Next return the whole solution to the dish by flooding the plate quickly and evenly.

The dish is then gently rocked, causing the developer to flow backwards and forwards.

After the space of one minute if no image appears pour another drachm of the ammonia solution into the meas ure, and pour on to it the developer from the dish, again flood the plate with the strengthened solution, and continue the rocking motion. If the plate has been correctly exposed the image should now make its appearance, the high lights coming up first. If not, another quantity of the ammonia solution must be added in the same manner as described, and the solution returned to the dish. The image will now gain in density and opacity, and it should be examined from time to time by the light of the lamp. The back should also be examined for the appearance of the high lights. When the required density is obtained, which is only arrived at by practice, the plate is removed from the developer and thoroughly rinsed in water. This done, it is removed to the fixing bath.

The process of development is one that requires considerable care and attention, and it is only by practice and patience that success is arrived at. To develop a plate which has received the correct amount of exposure to light is a comparatively easy matter, but to develop and make good printing negatives from plates which have been either under or over-exposed is where the skill of the operator is taxed to the utmost.

For beginners the ferrous-oxalate developer offers many advantages, although it possesses one drawback: i.e., there is less control to be had over it than with the pyro developer, and there fore it is almost essential that the exposure be correct, otherwise the method is a very simple one. Stock saturated solutions are made of potassium oxalate, iron sulphate, and ammonium bromide. To the iron a small quantity of tartaric or sulphuric acid is added to preserve. For developing we pour into a glass measure four ounces of potash solution, and add to it one ounce of the iron and three or four drops of ammonium bromide. Dilute the whole with an equal quantity of water and flood over the plate. If the image appears too quickly (the result of over-exposure) about 20 drops of the ammonium bromide restrainer must be added to the developer. If, on the contrary, the image is slow in appearing, a little more of the iron solution may be added. If too much be taken, however, a yellow precipitate of ferrous-oxalate will be formed, and the developer spoilt. With this developer the image should be allowed to get much darker than with pyro, as the density is very deceiving, and becomes much lighter when placed in the fixing bath.