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 8×10 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 formulæ 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 5×7, 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 [p178] 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 restrainer; 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 [p179] taken out and well washed. It should then be put
in the