So far the method of working considered has been that called single transfer, from the fact that the film of gelatine forming the picture is transferred from the paper on which it is prepared to a new paper basis which forms the final support of the print. This method of working involves the disadvantage that the picture is reversed, a matter of little importance in many subjects, but very serious in others.
For those subjects in which it is essential that the picture should appear in its correct relation of right and left, a second transfer is necessary.
For this purpose the print must be developed on a support that shall hold it in the same manner as the single transfer paper while it is wet, but allow it to be re-transferred to its permanent basis after development and drying.
The most simple method of working is by means of what is called " flexible temporary support," a paper very similar in general character to ordinary single transfer, but very much thicker and more heavily coated.
At least two or three hours before using, the surface must be prepared by rubbing over some waxing solution specially made for this purpose. It is readily procured with the temporary supports, and, like most photographic preparations that are only used in small quantities, more troublesome and costly to prepare than to buy. A little is poured on the face of the temporary support—the slightly glossy surface—and rubbed over the entire surface with a small piece of soft non-fluffy fabric. A second piece should be used to take off any excess, and ensure that the preparation is even and uniform, each piece being rubbed gently over the surface with a circular movement. Very little of the solution should be left on the temporary support, but sufficient to render it slightly more glossy than before the application. It should be freely exposed to the air for two or three hours to enable the solvents of the wax to evaporate and leave an exceedingly thin coating of wax only on the surface. After waxing it may be kept indefinitely before using.
In working, this temporary support is used in exactly the same manner as ordinary single transfer paper: the print has no tendency to leave it during development, and it may be handled with the same freedom. Considerably longer time should be allowed in the alum bath than is necessary for ordinary single transfer, as the temporary support holds the bichromate stain rather tenaciously. Twenty to thirty minutes should be sufficient.
After taking the prints from the alum bath they should be rinsed in three or four changes of water and allowed to dry before the second transfer is attempted. Drying should on no account be hurried, and if the prints are not to be transferred as soon as dry, the drying should be as slow as possible. If the prints are dried rapidly in a warm room, there is considerable risk of their leaving the temporary support spontaneously.
For the second transfer a specially-prepared paper is required, sold as " final support." It is a fine white paper of smooth surface with a thick coating of soft gelatine.
When it is required to finally transfer the prints, pieces of final support are taken slightly larger than the prints but smaller than the temporary supports, and soaked in cold water for about half an hour. The prints on the temporary supports are then soaked in water—which may be slightly warm with advantage—until thoroughly limp, about five minutes, and then one is taken and laid face upwards on the squeegeeing board, as much water as practicable being drained off. A piece of final support is taken from the cold water and immersed in warm—temperature about eighty degrees—for a few seconds, until the surface becomes soft and yielding. It is then laid face downwards on the print and firmly, but without much force, squeegeed into contact and hung up to dry. When perfectly dry it may be readily stripped from the temporary support, bringing the image firmly attached to it, by raising one corner with a knife and pulling the two apart. No part of the image should remain on the temporary support, which should be quite clean. The temporary support should be re-waxed, and is ready for use again. A large number of prints may be developed in succession on one piece of temporary support. It must be re-waxed every time.
The surface of a print developed on flexible temporary support is very similar to that of an ordinary single transfer.
During development the failures and defects previously mentioned in connection with single transfer are more probable when the tissue is on the temporary support, as in addition to the causes given there are others.
The most probable is that the temporary support is not in good condition. After using several times the surface will frequently become more or less dirty, and, however carefully it may have been treated with the waxing solution, fail to hold the print sufficiently. The temporary support must never be washed, the remedy would be worse than the state it was intended to rectify. It should be carefully cleaned with turpentine and re-waxed. If it still fails to work satisfactorily, it should be discarded and a new piece substituted. After using a number of times, the coating may frequently be injured, and then satisfactory working is impossible. If the cleaning with turpentine is resorted to occasionally before re-waxing, the temporary support may be kept in good condition for a much longer time.
Using a support too soon after waxing will inevitably result in blistering or frilling, as though the support were worn out. It is a good plan to wax all supports when the prints are taken off and put them away in a box for future use.
Failure of the print to strip from the temporary support may be due to several causes. The support may have been imperfectly waxed, and, consequently, it may hold the film too tenaciously. Or the final support may have been soaked too long in warm water and lost too much of its soft coating, and insufficient may remain to hold the film. If it is not allowed to remain in the warm water sufficiently long it fails to adhere, but. this is generally seen by bright lines appearing on the print where a deep shade abruptly changes to a light tone. The gelatine coating of the final support must be thoroughly softened, but not so much as to come away on being touched.