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Double Transfer 657

temporary, support, supports, water, wax and solution

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DOUBLE TRANSFER 657. Preparation of the Temporary Support.

A carbon print can be transferred, for develop ment, to a large variety of temporary supports, from which it can be transferred, when finished, to its final support. According as the surface of the temporary support is glossy or matt, the finished print will possess either a glossy or a matt surface.

Among others, the following may be used as temporary supports : Opal, glass, zinc, alumin ium, and enamelled iron, all of which may be polished or matt ; and also celluloid, sheet india rubber (hospital sheeting), and varnished paper.' Rigid temporary supports can only be used when the final transfer of the image is made on a flexible support.' The special papers don't require cleaning.

The temporary support, whatever it may be, must be coated with a film that will ensure adhesion of the pigmented gelatine during development. But this adhesion must be less than that of the image to the film of unhardened gelatine with which the final support is coated. These conditions are fulfilled by employing a mixture of wax and colophany, obtained by mixing the two following solutions, prepared cold-- 2 The light encaustic solution thus obtained should be kept in a well-corked bottle. A small quantity for regular use may be kept in a dropping bottle.

The glass or opal must be cleaned with a hot lye (a strong solution of washing soda), rinsed freely in plenty of water, dried at once, and polished with a fine fabric moistened with methylated spirit.

Zinc and aluminium should be cleaned thoroughly with a paste of whitening and water, then placed for a few minutes in a 2 per cent solution of hydrochloric acid and rinsed in plain water. They should then be dried rapidly, either near a fire or in a quick current of air or they may be dried by means of a cardboard fan.

Celluloid and india-rubber sheeting should. be cleaned with water containing a small pro portion of ammonia, then rinsed in plain water and dried with a thoroughly clean, fine fabric.

A few drops of the waxing solution should be poured on to the temporary support selected, and spread uniformly with a tuft of flannel.

A second tuft of flannel should be used to equalize the coating by rubbing with a circular motion, the circles crossing and re-crossing as in polish ing. It should be left for about an hour to permit the solvents to evaporate completely.

When any other support than the papers specially prepared is used for the first time, it is desirable to wax it several times. This ensures that the mixture of wax and resin covers the entire surface, including the depth of the grain.

After use, the temporary supports should be stored where they are quite free from dust. They can be used many times in succession without any other preparation than the appli cation of a very thin coating of the waxing solution each time that they are used.

658. Transfer on Temporary Supports. Paper temporary supports must be softened by being immersed in cold water for 10 minutes before the carbon print is squeegeed into contact. This time must be increased to about 30 minutes if the back of the paper has been rendered im pervious by either wax or varnish.

Supports which are completely impervious need only be immersed in water at the moment of bringing the carbon print into contact with them.

The transfer is effected under conditions identical with those already described for apply ing prints to their support in the single transfer process (§ 653).

659. Development. On account of the pres ence of the film of wax on the temporary support, development cannot be carried out at such a, high temperature when the print has been over exposed as in the case of a print finished by single transfer. It is, moreover, for the purpose of raising the melting-point of the wax that such a large proportion of resin is added to the waxing solution.' With the exception of this point, the develop ment of prints on a temporary support is carried out in exactly the same manner as previously described 654) for the development of prints by single transfer.

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