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Stripping

water, glass, plate, negative, film, dry, solution, collodion, films and gelatine

STRIPPING FILM.—Paper coated first with a solution of soluble gelatine, and then with a sensitive gelatine emulsion as used for dry plates. The paper acts as a temporary support during the operations of exposure. development, fixing, and washing, after which the film is laid face downwards on a prepared sheet of glass, and the paper removed with warm water, which dis solves the soluble layer, and leaves the image-bearing film upon the glass. The temporary per support is then replaced by a prepared sheet of gelatine called a stripping skin, and the whole stripped, when dry, from the glass. This process gives a clean, transparent flexible negative of superior printing quality, having all the advantages of glass without its fragility, and about one fiftieth of its weight. These negatives can be printed from both sides equally well, and are there fore very suitable for the carbon and photo-mechanical processes. The process of developing and fixing is precisely the same as with a dry plate. No alum bath should, however, be used previous to stripping. The following instructions are given by the Eastman Co. for stripping their film: While the films are washing, clean a glass plate one half-inch larger all round than the negative, and free from surface defects, and flow over it a thin layer of rubber solution, draining away all excess, and allow the surface to dry (say, for five minutes), then coat the plate with a plain collodion. The moment the collodion sets, wash well in cold water until the water runs from the surface without any appearance of greasiness, then place the collodionized4late face upwards in a dish of cold water, and bring into contact with it under water the paper nega tive film side downwards; grasp the plate and film by one edge with the finger and thumb, and lift the glass with the film attached slowly, allowing the water to drain from the opposite side. Lay the plate upon a table and place upon the back of the paper negative a smooth side of an indiarubber cloth (larger than the glass) and remove all surplus water by the action of a squee gee. The squeegee should be used firmly but without violence, the motion being in all directions. Remove the rubber cloth, lay the plate with the film upwards on a table, and place upon the film a double thickness of stout, clean, blotting-paper. Place a board or other flat surface over the blotting-paper, and on the board a weight of a few pounds. Proceed in like manner with all the washed films, always piling the last plate on the top of the blotting-paper covering the previous plate, and always place on top the blotting-paper, the board and the weight. In fifteen minutes the first plate will be ready to strip, but a much longer period may elapse if desired, provided the collodion varnish is not permitted to dry. The films will, however, strip perfectly after a lapse of several hours, if kept as directed.

Into a flat dish put water at about 120 deg. to zoo deg. Fahr., and, face upwards, in this immerse the first (or bottom) plate. Rock the dish slightly, and in a minute or two the paper will be found wholly or partly floating in the water. Remove it entirely with care. Remove

from the film with warm water and gentle friction with a soft hairbrush, or the soft part of the hand, any of the soluble gelatine that may remain attached to it. Wash well with cold water and immerse, if necessary, in the Saturated solution common alum in water 20 ounces Acid hydrochloric. ounce And if intensification is necessary, soak the negative in a saturated solution of corrosive sublimate, wash well, and blacken the image with a solution of io drops of strong ammonia to one ounce of water.

' All intensified or cleared negatives should be very carefully and very thoroughly washed in running water or in frequent changes of water for not less than two hours.

In a flat dish soak one of the stripping skins in cold water (in very dry climates soak in a bath of water containing five per cent, of glycerine and a few drops of carbolic acid. Place the plate under the skin in water and bring the skin into contact with the negative. Grasp the skin by the edge with the finger and thumb and lift slowly, allowing the water to drain from the opposite side. Remove all surplus water by the gentle action of a squeegee. Set the plate aside to dry gradually, say, for four or five hours at ordinary temperature. Trim the edges of the negative with the point of a sharp knife and strip it from the glass. Adhering rubber solution may be removed from the face of the negative or the glass by a tuft of cotton-wool saturated with benzine.

It is of the utmost importance that the stripping skin should not be soaked too long—other wise the glycerine will be entirely removed, and the finished negative will be hard and brittle, two minutes should be amply sufficient.

The back of the dried stripping skin may be coated with collodion before the negative is removed from the glass if thought desirable, or if a varnished negative is not required, the use of the collodion varnish may be dispensed with entirely.

Solutions used in developing the films should not exceed 75° Fahr., and the hands should only touch the films at the corners while wet to prevent softening of the soluble gelatine layer which holds the film to the paper.

For photo-mechanical printing processes and carbon single transfer, the negatives may be printed from while on the glass.

Printing from stripped film negatives may be done from either side if required, but the side that was in contact with the glass at the time of transfer is the correct side. The negative should be laid (preferably) on the convex side of finely-ground glass in the printing frame, ground side next to negative. This method gives fine soft effects, and prevents mottling of the print, caused by partial contact of the negative with the glass.

Gelatine films can be stripped from the glass plate by immersing in a weak solution of Hydrofluoric acid, Fluoride of sodium or of potassium. To prevent distortion of the image it is advisable to previously coat the film with a five per cent. collodion.