It will be well to remark here that freshly sensitized tissue will produce inferior pictures to that used a day or two after ; the pictures are not so hard, and there is less danger of the high lights being washed away.
Continuing Action of the carbon tissue, after exposure to the light, be kept in the dark for a little time the effect on the print will be precisely the same as if the exposure to light had been prolonged. This continuing action may often be utilized to advantage. Pictures known to be under-exposed will, if *kept till the morning, by that time have acquired the same force as if they had received the proper exposure. The action is accelerated by moisture; if kept in a very dry state in a drying cupboard it is arrested.
Development consists in simply dissolving the gelatine unaffected by light, with hot water as the solvent. Now, it will be seen that as the tissue is laid against the negative the parts acted upon by the light and rendered insoluble are on the surface of the gelatine film, the lower stratum next the paper remaining soluble. By placing the whole in warm water we should dissolve the lower portion of the gelatine film, detach the paper, and leave the insoluble picture floating about helplessly in the water, where it would soon be destroyed. To prevent this we attach the tissue to a rigid or flexible support to retain it intact whilst the proc ess of development is being carried on, for if the pigment film after exposure be placed in water for a short time and then laid upon any plain surface im permeable to water it will firmly adhere to it, provided precautions have been taken to carefully exclude the air from between the surfaces. It will also ad here to paper prepared with an insoluble gelatine film or any other colloid body, provided the two surfaces are brought into contact in a moist condition.
In transferring the pigment pict ure to a support, we obtain a reversed positive. For portraiture, seascapes, and many landscapes, this is often of but little disadvantage, and the picture may be developed by what is termed single transfer. For subjects which would be spoilt if reversed, what is known as the double transfer must be resorted to, un less in the first instance the negative was reversed.
Single the ex posed tissue in a bath containing cold water. It will first of all curl up, but afterwards lie flat and limp. It is then placed in another bath containing cold water and a piece of single transfer paper (paper coated with a thin and insoluble gelatine) which has been soaked in water for a little while. Bring them., together face to face, draw them out, and lay them upon a board, and force into close contact with a large squeegee ; then place between blotting paper for five or ten minutes. In squeegeeing, the tissue should be uppermost, and a sheet of waterproof cloth laid over it to prevent the squeegee from damaging it. Development should not be attempted for at least twenty minutes, during which time the tissue should be placed between sheets of blotting paper, and kept under pressure to ensure its adherence to the paper support. After that time it is placed in a dish, and water heated to a temperature of zoo deg. F. added. The colored pigment will at once commence to ooze out of the edges, and after a little time the paper originally holding the carbon film may be removed with the hand. Then, by gently laving the picture with the hand, the superfluous gelatine will be washed away, and if the exposure has been correct a perfect image should remain. A certain amount of control can be kept over a carbon picture. An over-exposed print will show itself by insolubility of the gelatine, the high light refusing to be washed clear. The temperature should be raised considerably, and hot water poured over with a jug (Fig. 94). If this fails to reduce the intensity, add a little ammonia to the water as a last resource, although the better plan is to make another print, giving less exposure. Under-exposure results in over-solubility of the gelatine. The half-tones will be washed clean away. It is rarely an under-exposed print can be saved. All that can be done is to reduce the temperature of the water. Development should never be hurried ; the slower it is the better the gradation of tone in the results.