Handbook of American Daguerrotype | Page 6

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. 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 a fine finish,
and similar had produced good impressions; these same plates, when subjected to a long
and light buffing, would present a surface no finer in appearance to the naked eye; but
upon exposure to the solar radiation, would produce a well-defined image in one fourth
less time than the plate without the extra buffing.

Coating the Plate.--For this purpose our mechanics and artists have provided a simple
apparatus called a coating-box, which is so arranged as to be perfectly tight, retaining the
vapor of the iodine or accelerators, and at the same time allowing, by means of a slide,
the exposure of the plate to these vapors. They can readily be obtained by application to
any dealer, all of whom can furnish them.
The principal difficulty in coating the plate, is that of preserving the exact proportion
between the quantity of iodine and bromine, or quick. It is here necessary to say, that
hardly any two persons see alike the same degree of color, so as to be enabled to judge
correctly the exact tint, i. e. what one might describe as light rose red, might appear to
another as bright or cherry red; consequently, the only rule for the student in
Daguerreotype, is to study what appears to him to be the particular tint or shade required
to aid him to produce the desired result. Practise has proved that but a slight variation in
the chemical coating, of the Daguerreotype plate will very materially affect the final
result.
The operator will proportion the coating of iodine and bromine or accelerators according
to the strength and composition of the latter.
Experience proves that the common impressions, iodized to a rather light yellow gold tint,
and brought by the bromine to a very light, rose color, have their whites very intense, and
their deep shades very black. It is also known that if you employ a thicker coating of
iodine and apply upon