The ferrotype and how to make it - The Grian Press

Foa. 117
What we call " Fog/' is a general obscuration
over the whole plate ; it may arise from the silver
bath, from the Collodion, or from diflfused light
in the camera-box, the plate-holder, or the dark-
room.
A silver bath, newly prepared, will in many
cases produce ])ictures entirely or partially ob-
scured by fog, in which case the fog is occasioned
by organic matter held in suspension in the bath,
which, being deposited on the plate during the
process of coating with iodide, on exposure turns
black, because it is more sensitive to the light than
the pure iodide of silver. To correct the tendency
to fog on the part of a new bath, add a few drops
of chemically pure nitric acid, the effect of which
will be to change the organic matter from a state
of suspension (which is that of floating in and
through the solution in innumerable fine atoms)
to a state of solution, which is to be dissolved in
the same manner as the nitrate of silver is dis-
solved by water. With a new bath, fog some-
times proceeds from an insufficient supply of
iodide of potassium, of which every new bath
should have nearly if not quite as much as it
will take up. (See directions for exciting the
bath in article on silver.) Sometimes old Collo-
dion will work well with a new bath, when a
sample of new will not work at all.
When the end or side of a plate is fogged, it
pnbably comes from the holder; the remedy ia