第3章

In the morning, before using the buffs, brush both as clean as possible, in order to free them from dust; then with the blade of a pair of shears, held perpendicular, rub the buffs from end to end; then knock them both together in order to free them from all dust or other substances, occasionally exposing them to the sun or to the fire.

With one of the buffs (reserving the finest and softest for the last operation), powder its face with fine rouge and brush off slightly, leaving only the finest particles in it. Every operator should have two plate-holders; one for cleaning and one for buffing the plate;for when using only one, the rotten stone is liable to get on the buff and scratch the plate.

Rest the fingers of the left hand on the back of the buff, near the farther end, with about the same pressure as in cleaning, while with the right you bear on the handle to correspond, and give the buff a free, easy, horizontal motion, passing it very nearly the whole length over the plate each time.

Continue this operation in such a manner that the plate will on all parts of its surface have received an equal amount of polish.

This buff once well filled with polish, add but little after, say a small quantity once in two or three plates.

The polish as well as the buffs must be kept perfectly dry.

The second buff should always be in the best order, and if this is the case, but little polish after the first need be used.

Much depends upon the last finish of the surface of the plate, and as a fine impression is desired in the same ratio, the operator must exercise care and skill in this operation.

Some buff the smaller plates on the hands, by resting them on the fingers in such a manner that the buff cannot touch them;some by holding the edges with thumb and little finger, with the remaining fingers under, or on the back; and others buff on the holder. When this last method is adopted, it requires the greatest caution to prevent the dust from getting on the buff.

The holder should be wiped clean.

The plate frequently slips off or around, and the buff comes in contact with the bed of the holder. When, however, the operator is so unfortunate as to meet with this mishap, the utmost care must be observed in thoroughly cleaning the buff cover before further buffing. In this last buffing it may be continued as before, except without the application of polish powder to the last buff.

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.

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.