Gelatine Plates for Stripping are in the market. In their preparation it is necessary to first coat the glass with a solution of yellow wax in benzole, or an indiarubber solution, before coating with emulsion, such plates being known as strippers in America and Germany. When finished, the negative is placed, together with a gelatine film—or “skin”—in a solution of glycerine and water, both are withdrawn together, a squeegee applied to remove the superfluous solution, and the negative, with its adhering skin, placed aside to dry. Afterwards the edges of the film are cut through, and the negative removed from the glass.
Stripping the Film off Gelatine Negatives for Collotype.
In the Photographisches Archiv, Mr. Wilh. Otto, a well-known German Collotype printer, describes the following process:—
“The glass plates are first cleaned by being well rubbed with a solution of caustic potash, after which they are thoroughly rinsed and polished with tripoli. The next proceeding is to wax them by rubbing one face over with a solution of 12 grains of beeswax to one ounce of ether, this being applied by means of a piece of cotton or linen cloth saturated with the solution. In polishing off the excess of waxing solution, care must be taken not to destroy the continuity of the extremely thin and almost invisible film of wax which it is necessary to leave on the glass to ensure the easy and complete separation of the film. Some operators prefer to wax the plates by warming them to a temperature somewhat over the melting point of wax, then rubbing one face over with a lump of the article, the excess being now polished off with a piece of flannel before the temperature of the glass falls below the melting point of the wax. It may be mentioned that, before waxing, it is as well to mark the working surface of each plate by making a diamond scratch in one corner.
“A small piece of cloth, moistened with ether or benzole, is now used to remove all traces of wax from the edges of the plates, a margin of the width of an inch being sufficient; and it is well to paint this margin with albumen and to allow it to dry. Unless the edges of the plate are entirely free from all traces of wax, there will be a great probability of the film separating from the glasses at too early a stage, and adhesion at the edges is made more certain by the use of albumen. A moderately diluted solution of silicate of soda may be used instead of albumen.
“The waxed side of each glass is now coated with collodion containing a little castor oil; eight grains of tough pyroxyline and three drops of castor oil to each ounce of mixed solvents (equal volume of alcohol and ether) being a convenient preparation.
“The collodion being dry, the plates are coated with emulsion. The emulsion flows very badly on the collodionised surface, but by using a bow made of a piece of sewing cotton stretched across an arc of thin iron wire the difficulty may be readily overcome. The thread is to be drawn over the surface of the plate after the required quantity of emulsion has been poured on, and it is scarcely necessary to say that the glass should be supported on a levelling stand.
“Plates prepared in this way are developed and fixed in the ordinary manner, and when a plate is dry it is sufficient to cut through the film inside the edge which has been cleaned of wax, when the film negative can be easily stripped off. In this case, however, the film is very thin, and it is often desirable to thicken it somewhat before stripping. For this purpose a piece of thin commercial sheet gelatine is taken, and soaked in water till it becomes quite flaccid, and this is laid on the negative, care being taken that no air is enclosed between them. A sheet of wet paper, or of mackintosh, is now laid on the gelatine film, and all excess of water expelled from between the negative and the soft gelatine film by stroking the upper surface of the paper, or of the mackintosh cloth, with a squeegee—that is to say, with a strip of indiarubber set in a wooden handle.
“It is now easy to remove the paper or the indiarubber cloth which was used to protect the soft gelatine from the action of the squeegee, and the plate can be set up to dry. When dry, the film is cut through within the border from which the wax was cleared off, and the film will separate readily; but should there be any tendency towards a too early separation, owing to the contractile force of the fresh thickness of gelatine, the edges of the plate may be bound with strips of gummed paper.” (Photographic News.)
Stripping Ordinary Gelatine Plates.—Any make of dry plate may be stripped by the following method:—The plate is coated with strong tough collodion upon the gelatine side; as soon as the collodion has set, it is plunged into cold water and washed until all greasiness disappears. In the meantime, a piece of “flexible support,” as used in carbon printing, is carefully waxed by rubbing upon its surface a solution of turpentine 140 cc., beeswax 2 gm., resin 6.5 gm. This should be applied evenly by means of a piece of flannel, the solvent allowed to evaporate, and the waxed surface polished with a second piece of flannel. The support should then be placed in cold water and allowed to become quite flexible, in which state it may be used at any time. Remove the negative from the clean water, and place in a bath of methylated spirits 150 cc., glycerine 3 cc., water 30 cc., hydrofluoric acid 3 cc. An ebonite, guttapercha, or lead dish should be used to contain this solution, with which the fingers should come in contact as little as possible. The film should be watched narrowly, and when loose upon the glass—but not actually detached—the plate, still bearing the film, should be placed in a bath of clean water, well washed, and all surface moisture absorbed by careful blotting. Take the flexible support from the water in which it has been standing, and without removing any adherent moisture, carefully lower it upon the film, which is still resting upon its original glass plate, squeegee it into contact with the negative film, avoiding air bubbles, place under a weight, and allow to stand for ten minutes or a quarter of an hour. The film will then be found to adhere to the flexible support, and may be readily removed from the glass. It should be allowed to dry spontaneously upon the support, no attempt being made to remove the film until it is “bone” dry, when it will readily part with the temporary support, remain perfectly flat, and may be printed from either side with perfectly satisfactory results. Should any of the waxing solution remain on the surface of the film, it may be removed by the careful application of a little turpentine applied on a small linen pad. Do not use methylated spirit for this purpose, as it may cause the film to “buckle.” Any stripped films may be conveniently preserved and kept flat between the leaves of a book.