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 LIGHT.--If 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 of light may often be utilized to advantage. Pictures known to be under-exposed will, if kept till morning, by that time have acquired the same force as if they had received the proper exposure.
DEVELOPMENT consists simply in dissolving the gelatine unaffected by light, with hot water as the solvent.
Immerse the exposed tissue in a bath containing cold water. It will first of all curl up, but afterward lay flat and limp. It is then placed in another bath containing cold water together with a sheet of glass which has previously been coated with a 5 per cent. solution of gelatine. Bring them together face to face, draw them out, 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 American 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 glass, with the tissue on it, should be placed between sheets of blotting paper, and kept under pressure to insure its adherence to the glass support. After that time it is placed in a dish, and water heated to a temperature of 100 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 leveling 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 an autotype picture. An over-exposed print will show itself by insolubility of the gelatine, and the high light refusing to be washed clear. The temperature should be raised considerably, and hot water poured over with a jug. If this fails to reduce the intensity, add a little ammonia to the water as a last resource, though 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.