The ferrotype and how to make it - The Grian Press

COLLODION. 67
can not be diminished beyond a certain point
(depending on tlie Collodion used), without a
grea/ loss of sensitiveness; or what is exactly
similar, if we use a bath of a certain strength,
the quantity of iodide can not be increased to
any amount, but must be limited by the propor-
tion of nitrate of silver. With a thi-rty-five grain
solution of the latter, four grains of bromo-
iodides, or iodides and bromides, answers very
well ; but if the quantity be increased to six
grains, there is a great loss of sensitiveness, the
effect being similar to that arising from an in-
sufficient amount of alcohol in the Collodion, in
consequence of the iodide of silver being de-
posited superficially, or even falling off the sur-
face into the silver bath. It will be well to note
here, that the formulas for Collodion herewith
given require a silver solution of at least 45
grains to the ounce, and will work much better
with a fifty grain solution.
By knowing the quantity of iodide contained
in a Collodion, it is easy to ascertain the amount
that the bath loses for each ounce, and thus to
know exactly how much nitrate should be mixed
to maintain the strength ; thus, with a Collodion
containing eight grains of iodide of ammonium
to the ounce, each ounce expended removes nine
and four-tenths grains of nitrate, but with iodide
of potassium, the quantity removed would be
elightly less.
For the purpose of pouring the Colh^^ion over