Turning the film has now to be prepared for turning, otherwise the picture would appear reversed in the after printing. Though to turn it is by no means a difficult opera tion, it requires delicate handling, and is most interesting. To enable its being so turned it is first giving a coating of india-rubber dissolved in benzole, made as follows : Cut half an ounce of pure virgin rubber into small pieces, and place in a bottle with about 8 ounces of benzole, giving it a good shake occasionally. In a few days it will dissolve. It should be about the same con sistency as good collodion, and if found too thick it may be thinned by the addition of more ben zole. It must not be too thin, however, otherwise it will not be sufficient to resist the action of the collodion which is to be afterward applied and which would eat away and destroy the film. After the benzole has evaporated and left the rubber in a thin layer dry over the film, it must be flowed over in the same manner with " stripping " collodion, made after the following recipe : Alcohol 4 Pyroxyline 60 grains.
Sulphuric ether 4 ounces.
Castor oil 3o drops.
The castor oil is added to make the film adhere to the glass after being turned. It is ready for turning any time after the collodion has set and dried.
At this stage the film should be cut through with a sharp knife about a quarter of an inch from the line marking the margin of the picture. It is now to placed in a solution of acetic acid, of quantity sufficient to cover well, and proportioned as follows : Acetic acid z ounce.
Water 8 ounces.
In a few minutes the film at the outer edges will readily be picked away by raising it at the corner with a penknife. After stripping away the outer portion, and leaving only the picture on the glass, put under the tap and wash well, but carefully, and lay on a table, with plenty of water upon it. Now take a piece of stout common printing paper, somewhat larger than the pic ure and within the size of the glass ; wet it by drawing it through water, and lay it over the film ; next squeegee the water from till smooth, raise the corner, and with the point of a pen knife pick up the corner of the film, just enough to catch hold of it between the finger and thumb, keeping the paper for support, and gently pull both together from the glass. It will readily come away. Lay it down upon the glass, film up, and smooth out gently with the squeegee, or the point of the fingers, any wrinkles that may have come on it. If the wrinkles are numerous, or the film too delicate to handle with the squeegee or the fingers, a gentle flow of water will expedite the operation, being cautious, however, not to flow so sharply as to float it off ! Now draw another piece of paper through water, and lay it over the film, squeegee again, and lifting both papers, having the film between them, from the glass turn right over, and remove the first piece of paper, which will now be uppermost. The film may now be lifted with its paper support
and set aside, and the glass thoroughly cleaned under the tap. So cleaned, lay the glass on the table with plenty of water, lay the film, with its paper support uppermost, in the center, and squeegee the water from it. The paper may now be lifted and the film examined and smoothed out gently with the squeegee, and the paper replaced over it. With two or three layers of blot ting paper over it, it should be placed under a board and a weight for about half an hour, when it may be taken out and set side to dry.
Preparations for negative is now ready for being printed from, and the student's attention will now be directed to the preparation of the metal plate for etching. This may be either of zinc or copper, the choice being determined by circumstances, it may be of economy or otherwise. It has been maintained by many excellent operators, especially in Eng land, that one metal is as good as another, so far as the final results are concerned ; but an examination of the work in America will satisfy an unprejudiced scrutiny that finer effects have been obtained on copper. It is possible that different ideas of what constitutes excellence in an engraving may account for the preference. It will be noticed that the American workman seeks after strong contrasts of light and shade, and, not content with that which his negative can sup ply,, has recently resorted to putting the strong lights in with the graver, and by rubbing down the dots has strained after deeper blacks in the shadows. Our cousins on the other side evidently seek after softness of general effect, and by their writings on the subject show that they esteem this 'as the acme of attainment. Whichever metal is chosen, however, it must be perfectly polished. It may be purchased in several grades of preparation, rough, machine polished, or highly buffed. We think it the best economy to get at least machine polished, and we will assume that it has been so procured.
Polishing the the metal chosen be zinc, it may be brought to a good polish under charcoal and water, but with copper it is necessary to give it a fine grain with emery and charcoal and water, and lastly with charcoal and water alone. In polishing on either metal, let the rubbing be done all one way, to and fro, not in circles or across. After a partial polish, it is well to put it for a few minutes into a strong lye, to overcome any greasiness; and the hands should be perfectly clean, and the fingers not allowed to touch the polished surface of the plate for the same reason.