Hence we see that the plate should be buffed just before receiving
the vapor of iodine. Mr Hunt gives his opinion of the use
of diluted nitric acid as the best solution for freeing,
the surface of the plate; he says:

"Numerous experiments on plated copper, pure silver plates,
and on silvered glass and paper, have convinced me that
the first operation of polishing with nitric acid, etc., is
essential to the production of the most sensitive surface.
All who will take the trouble to examine the subject, will soon
be convinced that the acid softens the silver, bringing it
to a state in which it is extremely susceptible of being either
oxydized or iodized, according as the circumstances may occur
of its exposure to the atmosphere or the iodine."

I cannot see the objection to this solution; not, however, in general use.
Our operators do not find it of sufficient importance to the success
of their pictures to accept it, the alcoholic solution being in its
nature less objectionable.

I will say here, that a plate submitted to only an ordinary polish
is found to contain numberless minute particles of the powder
made use of. Should the same plate be buffed for a long time,
the polish will nearly all disappear, leaving the cavities
in the surface free for the action of agents employed in
subsequent operation. For this reason, I find that great amount
of polishing powder should not be applied to the last buff,
and it is obvious that three buffs can be employed to adventure;
the two last should not receive any polishing materials.
I have examined a plate that was considered to possess