The production of photographic images making use of the intensity-reversal effect

摘要

882,690. Photographic materials and processes. EGGERT, J. March 11, 1959 [March 11, 1958(3)], No. 8418/59. Class 98(2). A photographic silver halide emulsion containing silver iodide and which has been subjected to physical ripening in the presence of an inhibitor but which has not received chemical ripening, is given a flash exposure of maximum duration 10-2 secs., and then an imagewise exposure of lower intensity than the flash exposure. By making the flash exposure uniform, a reversal effect is obtained. The flash exposure may be a single exposure or a number of flash exposures of lower intensity. It may be given before the emulsion is cast on its support. Alternatively, the flash exposure may be given through a screen. Compensated prints may be made according to the invention from negatives having a large density range by making the flash exposure a sharp imagewise exposure and then giving an outof-focus exposure of lower intensity, for example by covering the printing paper with a sheet of opal glass. In this embodiment, the procedure may be modified by giving the outof-focus, low intensity exposure first, and then the sharp flash exposure. The emulsion is prepared by precipitating the silver halides at 40- 90‹C. in a protective colloid such as gelatin, preferably in the presence of excess watersoluble bromide, and then physically ripening the emulsion in the presence of an inhibitor or stabilizer such as a 1;3;4-triazaindolizine, a benzotriazole, hystidine, 2-ethyl benzoxazole, N-ethyl pyrrole or 2;3-dimethyl quinoxaline. The emulsion is then washed, but not subjected to chemical ripening. The emulsion or developer may contain thallium salts such as the nitrate. Specifications 619,557 628,994, 636,144 and 636,145 are referred to.