Examine the surface occasionally, and buff more lightly towards the close of the operation, using at last the mere weight of the buff.

This last buffing should occupy as long a time as the first.
The point to be aimed at is, the production of a surface of such exquisite polish as to be itself invisible, like the surface of a mirror.

The secret of producing pictures discernible in any light, lies in this: the more dark, deep and mirror-like the surface of the plate, the more nearly do we approach to perfection.
In all cases, very light and long continued buffing is productive of the greater success, since by that means a more perfect polish 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.