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.

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.