Make a saturated solution of yellow prussiate of potassium and dilute with an equal bulk of water; add 2 drops of ammonia and 2 grains of dry pyro to each ounce used.

The solution can be used repeatedly until exhausted. Four ounces of this solution would contain 8 grains of pyro, which is enough to develop 2 8x10 plates, or their equivalent of smaller plates. Mix only the amount that will be used at one sitting.

It will be noticed in all the foregoing formulae that the matter of greatest uncertainty is the exposure of the plate; you never can tell if your plate is properly exposed until you begin to develop, and then if your picture flashes out at once it is too late to correct by modifying the developer.

The theory of development is that the pyro is the developing agent and gives the strength.

The soda, or ammonia, as the case may be, gives the detail. The bromide is a restrainer, and to a certain extent will correct over-exposure. Sulphite of soda, citric acid and sulphurous acid are used to keep the pyro from oxidizing.

Therefore, when developing a plate, say a 5 x 7, put it in the tray and pour over it the amount of pyro necessary to develop such a plate, say two grains in four ounces of water, let the plate remain in this solution for a short time, in the meantime take of your alkaline solution the amount you would use for the same size plate, but add only a small portion to the solution covering the plate. To do this pour off the pyro solution into a graduate and add a drop or two of the alkaline solution, soda, potash or ammonia, whatever it may be, then turn the solution back on the plate and watch for the effect; if in a few minutes there is no change, then add more of the alkaline solution in the same manner, and in a short time the image will begin to appear; if it comes up too slowly, give it the remainder of the alkaline solution, and unless the plate has been under-exposed the image will come out and strengthen gradually until it has well sunken into the plate, when it may be removed and washed.

If you use the oxalate developer, proceed upon the same plan; oxalate in the place of pyro, iron in the place of alkali, but always add the iron to the oxalate, not the reverse.

Do not be persuaded that the bromide is only a re-strainer; it is that and more too; it may greatly affect the quality of the negative, making it much finer in grain and clearer in the shadows.

Under-exposed plates at best make but poor negatives, and it is preferable to err, if at all, on the other side, but with the rapid plates now made exposures are very seldom too short.

When the plate has been developed it must be washed and then placed in the hypo solution to fix.

The most effective strength of hypo solution is half saturated. Make a saturated solution of hypo and dilute it with an equal bulk of water. The plate should lie in this solution until it appears perfectly clear, and about five or ten minutes longer, then it should be taken out and well washed. It should then be put in the Clearing Solution.

Clearing Solution

Water, ½ gal. Alum, ¼ lb. Citric acid, 2 oz.

Allow the plate to remain in this solution a few minutes and it will be found to have been greatly improved, having lost the color and cleared the shadows. This solution, besides clearing the negative, decomposes the hypo remaining in the film, and a short wash after being taken from it is sufficient.