Every manufacturer of dry plates encloses in each box of plates
packed for the market a formula for the development of the same.
The various manufacturers of dry plates, whose names will be found
in the advertising pages in this book, each have a formula which in
some respects differs from all the others, and it is but fair to the
maker of the plate, that his formula should be used, unless the
operator is of much experience and understands the requirements of
each particular kind of plate.
Therefore, while formulæ are given in this connection, although they
are known to be of the best, yet in the hands of inexperience they
may result to no better advantage than the formula appropriate to
the plate used; consequently, we do not urge their use above any
other, but rather that to which the operator is most accustomed.
The alkaline pyro developer is now in general use among professional
photographers in this country, and there remains no doubt that it is
the best developing agent for dry plates that has yet been brought
into use.
This developer is composed of pyrogallic acid and [p055] an
alkali, either ammonia, sal soda, or carbonate of potash, which, in
solution and of proper strength, forms the medium through which the
pyro is applied.
To these is added bromide of potassium or ammonium, which is the
restrainer, and occupies about the same position or performs the
same function as acetic acid in the wet plate developer, and besides
being a restrainer it greatly aids in securing intensity and
printing quality; and when plates are overtimed in exposure its
prompt use may result in securing a good negative.
Some plates require double the quantity of pyro that others do to
produce the same quality of negative. After ascertaining the normal
amount of pyro necessary to develop plates of a certain make, if it
is desired to increase intensity add more pyro, if your plate is
developing too intense or hard add more of the alkali.