FILM MANIPULATION The use of films, both flat and rollable, has become during recent years more and more popular, and there has been much discussion as to whether these or plates are the more advantageous, although, results alone con sidered, there is no difference between them. The developers, fixers, intensifiers, etc., suit able for dry plates will suit films also, for the reason that the emulsions are the same although the support is glass in the first case and cellu loid in the second.
Flat films are treated exactly as though they were plates. There may be difficulty in keeping them wholly immersed in the solutions, on account of their buoyancy, which tends to make them float on the surface of the liquid, thus leading to uneven develop ment, markings, and yellow stains. It is best first to place the required amount of developer in a dish and to slip the film face upwards into it well under the surface ; or the film may be placed in a dry dish and the developer poured on. By rocking the dish the film is kept on the move, and the developer made to flow evenly over it. Some workers use a narrow wooden frame A, which tightly fits the bottom of the dish ; the film is then pinned face upwards to the frame and the developer poured on. But this method ought not to be necessary except that films tend to curl very much when wetted. The disadvantage of using a false bottom entirely of wood is that unless it fits very tightly in the bottom of the dish it may float on the surface and do more harm than good.
Cutting Roll Films.—Only when roll films are threaded, the whole length of film being worked backwards and forwards through the developer, which should cover the bars. In a contrivance, C, embodying the same principle, a bent rod carries a roller acting as a bar to keep the film under the developer ; with both these contrivances it is necessary to hold one end of the strip in each hand after the manner shown at P. A con unrolled in a proper way is there little or no danger of cutting through the images. The cutting up of a roll film before development is necessary only when each exposure is to be developed separately, after the manner of flat films. D shows the proper and E the improper method of cutting up a roll film. The roll should be held in the left hand and the end of the wound-up film pulled with the right, the black paper being on the top and the film beneath. Only one number should be unwound at a time, and when the division marks at the edges are seen (between the numbers), the film is placed in contact with the black covering paper and both cut through evenly with a pair of scissors ; by this method the paper and film are in con tact and in agreement as in the camera. The wrong way of cutting up a film (see E) is to bring the loose white film to the top of the black paper, because when this is done the images will invariably be cut through, as the division markings will not be true. The film must be swung round below the paper, in the direction shown by the dotted lines.
Developing Roll Films.—The object of cutting trivance on a different principle is shown at G; one end of the film is attached to a spring drum, which is made to revolve, and the film passed through the developer by alternately pulling and slackening the other end. These
and other accessories are very convenient, but in their absence the following method may be adopted. A dish is filled with the developer. The whole length of film is detached from the black paper, one end is taken in each hand, and the film is passed, sensitive (matt) side down wards, through the developer, a see-saw move ment of the arms being maintained, and the film passed to and fro through the developer until the whole series of images is fully developed. It is a good practice to develop the whole strip until the barest outlines are visible, and the spaces dividing the pictures can be distinctly seen ; the film can then be cut with scissors, the partly developed pictures placed in cold water, and each one developed separately in an ordinary up films is to avoid the awkward operation of developing them in the strip form. With the shorter lengths there is, however, no difficulty in developing them whole, but when longer than 36 in. it is better to cut them up or to use one of the numerous film-developing devices on the market, which, of course, are suitable for the shorter lengths also. At B is shown a dish having two cross-bars, under which the film is flat dish. It is advisable to keep the partially developed films on the move while in the water, as, if allowed to stand, they may remain curled up or on the surface, in which case markings and stains would appear.
Fixing.—Pilms may be fixed in the strip, or cut up. Even if the film is developed in strip form, it may be advisable to cut it up before or during fixing, for the sake of convenient handling ; but opinions differ on this point. Films need more care than plates when fixing, because, should the films float on the surface of the fixer, exposure to the air will cause markings, yellow stains, etc., which cannot easily be removed. An acid fixing bath (potassium metabisulphite and " hypo ") is better than an ordinary fixing bath of plain "hypo," as the metabisulphite prevents stains.
Washing and Drying.—Films cannot be washed and dried in a rack like plates, and some trouble is often met with in keeping them under the surface of the water. Numerous devices have been introduced for washing films properly. A useful contrivance is shown at H ; a cork is cut in halves lengthways, after cutting a notch in the top ; then an indiarubber band is placed around the halves as shown, the whole now forming a clip. The film is inserted in the cork, which will float on the surface of the water and hold the film beneath the surface. Films are best dried by pinning them, face (emulsion sur face) outwards, to a shelf, as shown at I, or special clips may be used in place of pins. All flat films should be kept under slight pressure when not in use. If a film is stored in a roll, it should always be wound sensitive surface outside, as it will then lie flatter when printing. Films are better varnished, and for wet films a borax and gum lac solution is best, but for dry films a dammar varnish may be used. (See " Varn ishes.") By the aid of special tanks, the develop ment of films may be carried out in daylight.