Rigid temporary supports are sometimes used for double transfer, consisting of finely-ground opal glass. They produce prints with a" matt surface in place of the slight gloss resulting from the use of the flexible paper supports. They are used in all respects similarly to the flexible supports—waxing, developing, aluming, and drying—but they are rather more troublesome, as they do not hold the film so well, especially in prolonged development.
Recently two new papers have been introduced for final supports for double transfer, a fine grain white and a similar paper toned. These are used in the same manner as the final support previously described, excepting that it is absolutely essential that the flexible temporary support be employed. The fine grain of the paper is well preserved in the final appearance of the print, and it is an agreeable change from the perfect smoothness of the usual final support. The toned variety is specially useful for some colours.
Prints may be developed on opal by single transfer, the method being exactly the same as for ordinary single transfer on paper, no preparation of the opal being necessary.
Very finely-ground opal glass must be used, a suitable kind being supplied by the manufacturers of carbon tissue and materials. As in using opal glass for double transfer, the ground surface must be used.
As there are many subjects for which double transfer is a necessity on account of the reversal of the picture being inadmissible, it has been felt to be an objection that so little choice of paper as a permanent support existed in the case of double transfer—until recently only plain smooth white— in contrast to the variety of tone and texture available for single.
The fine grain white and toned final supports previously mentioned form a considerable improvement, and for many workers will probably fulfil all requirements. For those who desire the same variety as in single transfer, however, and are prepared to take a little extra trouble, the following method of obtaining prints by double transfer on any kind of paper, which has been successfully employed in the author's practice during the last three or four years, will probably appeal, as it gives the opportunity of obtaining a much greater variety than by using commercial supports.
The paper must be prepared by giving it three or four coatings of a solution of gelatine, one ounce in thirty ounces of water, in a similar manner to that described for preparing paper for single transfer; but a thicker preparation is necessary, and no chrome alum or other hardening substance should be used. Nelson's No. 1 gelatine is the most suitable, though other kinds may be substituted. The prepared paper will keep indefinitely. a pint of gelatine solution should be sufficient for giving one coating to five or six sheets of imperial size drawing-paper.
The prints must be developed on flexible temporary support, and dried before transferring, the whole working up to the time of transferring being exactly similar to the ordinary double transfer.
When ready for transferring, a solution of gelatine must be made—half an ounce to seven or eight of water—and the prints thoroughly re-wetted and the drawing-paper final support also soaked in cold water for a few minutes. The prints may with advantage be immersed in warm water for a few minutes, but only cold must be used for the drawing-paper, on account of the solubility of the gelatine. Nelson's No. 1 gelatine is the best to use for the transferring solution, and instead of weighing out small quantities the following plan may be adopted for mixing. a quantity of gelatine is taken and soaked in cold water for ten minutes or more, and then the water is drained off as closely as possible, and the gelatine dissolved by the aid of heat in the water that it has absorbed only. The solution is measured and diluted by adding hot water until it measures three times its original volume. It must be kept as hot as possible a print on the temporary support is taken from the water, carefully blotted to remove as much of the adherent water as possible, and laid on the squeegeeing board, a piece of the prepared drawing-paper taken and similarly blotted off, some of the hot gelatine solution poured on to the centre of the print and rapidly spread over its entire surface, care being taken to avoid air-bubbles or uncovered patches, the drawing-paper laid face down and firmly squeegeed into contact. At least half an ounce of gelatine solution must be allowed for a whole-plate print.
When dry the print may be stripped from the temporary support in the usual manner, and retains the texture of the paper admirably. It is necessary that the gelatine preparation of the paper and that uniting the print with the paper should be hardened, and for this purpose the prints should be immersed in a solution of formaline—one part to ten or twelve of water—rinsed in several changes of water and dried. The slight gloss left by the temporary support may be entirely removed by immersing the print in hot water for a few seconds, at any time after the formaline bath.
The temporary support acquires the texture of the paper used, but this is unimportant, as this grain entirely disappears on immersion in water.