can be obtained.

The question is often asked, why is it that the plates receive the coating
so unevenly? I will answer by saying that it may arise from two causes:
the first and most general cause is that those parts of the plate's
surface which will receive the heaviest coating have been more
thoroughly polished, and the consequence is that it is more sensitive
to the chemical operation. second. and might perhaps be considered a part
of the first, the heat of the plate may not be equal in all its parts;
this may arise from the heat caused by the friction in buffing.
It is a well known fact, with which every observing practitioner
is familiar, that a silver plate at a temperature of 45 deg.
or less, exposed to the vapors of iodine, is less sensitive and takes
a longer time to coat, than when it is at a temperature of 60 deg.
or more.

Whenever a view is to be taken, or any impression which requires the plate
to be turned on the side, it should be buffed in the other direction,
so that the marks will always be horizontal, when the picture is in position.
With the finest possible polish, the plate is ready for the coating box.

The question is often asked by operators, what is the state of the
plate when polished and allowed to stand for a time before using?
To meet this point we hare only to consider the silver and the power
acting upon it. Pure atmosphere does not act upon silver;
but we do not have this about in our operating rooms, as it
is more or less charged with sulphurated hydrogen, which soon
tarnishes the surface of the plate with a film of brown sulphurate.
It is this that sometimes causes the specks which appear
on finishing the impression, and are a great annoyance.