This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Preparing Developer. Each plate manufacturer has special formulae particularly adapted to their own plates, which are the results of very careful experimenting, guided by a full knowledge of the exact ingredients in the emulsion. The formula recommended by the maker of any particular plate is undoubtedly the best, but the following formula is a good all-round one, and with it fine black tones can be produced. By increasing the exposure, and by the addition of more Bromide of Potassium (10% solution) when developing, warmer tones can be secured. 903. Sulphate of Iron Developer.
Stock Solution No. 1.
Oxalate of Potash............................
Ammonium Citrate Solution..................
Stock Solution No. 2.
Sulphate of Iron..............................
Place these solutions in separate bottles, marking them Stock Solution No. 1 and Stock Solution No. 2.
Preparing Ammonium Citrate Solution. The Ammonium Citrate Solution is made by dissolving 1/4 ounce Citric Acid in 1 1/2 ounce of water. Add a few drops of strong ammonia water, enough to neutralize the acid. Then add sufficient water to make two ounces in all. This solution can be purchased all ready prepared, or can be made up as above.
Sulphate Of Iron. Proto-Sulphate of Iron, should be bright bluish-green crystals which disintegrate in air. Soluble in water. If they are dull and rusty, caused by oxidization, do not use them; get fresh clear crystals.
906. This developer gives fine, black-toned positives, and beginners should not try for other tones until they have absolute control over both exposure and development.
Developing. To develop, prepare the developer as follows: Pour 3 ounces of Stock Solution No. 1 into the graduate; add to this 1 1/2 ounce of Stock Solution No. 2; add 3 drops of a 10% solution of Bromide of Potassium. Place the lantern-slide plate in the tray and pour the developer over the plate in the usual manner, being careful to remove all air-bells.
908. It is a very good plan to have a small piece of absorbent cotton, thoroughly saturated with developer, in the developing tray, using it to swab the entire surface of the plate. This will remove air-bells and dirt. These air-bells or dirt would cause transparent spots on the slides. As lantern-plates are not nearly as rapid as ordinary plates, a brighter developing light can be used. A light made non-actinic by a couple of thicknesses of post-office paper will be safe.
909. With a strong light the development can be watched closely, and stopped when the transparency has reached its best.
910. To more readily see the plate come up, always develop in a white porcelain dish, or have a piece of white paper under the plate, and use a fresh piece for each plate.
911. It is impossible to state a definite time in which the plate must be developed, because this will be found to vary according to the character of the negative from which the slide is being made, the temperature of the solution, and, to a certain extent, according to the subject. Ordinarily, the formula given will furnish a fully developed slide in about five minutes.
912. The principal difficulty will be found in determining how far to carry development. This can only be ascertained by practice.
913. For the first lantern experiments it is advisable to develop the plate until all detail is clearly visible and the transparency appears crisp and snappy. At this stage the plate is developed, but be careful to time the operation of the first experiments. If the plate is too dense, or too thin, after fixing, figure accordingly in developing the next slide.
914. A lantern-slide must be so transparent that when laid upon printed paper the small letters can be easily read through the transparent shadows; the high-lights, of course, will be slightly denser, but not as much so as in a printing negative.
915. Usually, when the image on the transparency reaches the stage where it begins to veil over, which indicates that it is fully developed, remove the plate from the developer and carefully wash under the faucet for two minutes, with a slow stream only, so as not to injure the film.
916. There is no particular difference between the development of a lantern-slide and an ordinary negative, except that the lantern plate is not carried so far, and that the color of the film is important (that is to say, it must be a pleasing color), whereas in a negative it matters little what the color is, provided it gives good prints.
917. Lantern-slides must be free from fog, which may be caused from over-exposure or over-development. If the slide is over-exposed, add a few drops of bromide to the developer, to prevent fogging, but it is very seldom that such a slide can be made perfect.