Patent GB-599392-A (GB)
Title: Improvements in line and half-tone photographic reproduction
IPC: G03F1/54
Filed: 1945-05-26
Abstract: 599,392. Photographic printing processes. KODAK, Ltd. May 26, 1945, No. 13210. Convention date, May 26, 1944. [Class 98 (ii)] In printing a minutely detailed two-tone original by an infinite gradient process, the original is, at least during the major part of the printing operation, in register and in printing relation with a diffuse mask of complementary density thereto having a masking factor between 0.2 and 0.7 and whose diffuseness is sufficient to cause the finer details of the original to be substantially lost in the mask. In a modification, the mask may be out of exact printing relation with the record. Alternatively, the mask may be sharp, but sufficiently far out of exact printing relation to cause the finer details of the mask to be substantially lost. The record masked may be the line or half-tone original, in which case the resultant negative or any one of a series of successive prints may be processed to an effective infinite gradient, or may be a negative of the original, in which case the resultant positive or print thereof may be processed to an effectively infinite gradient. The mask may be held integrally in register with the record even when being processed. Part of the printing exposure may be unmasked. A mask may be made by spacing the sensitive material on which it is to be produced a short distance away from the drawing and printing with a diffuse, preferably annular, light source. When printing from a. masked combination, the slight magnification of the unsharp masking image compared with the image from which it is produced is compensated for by arranging the mask behind the masked image. As shown in Fig. 2, the original 60, with two close dark elements enclosing a fine light detail 61, is illuminated by lamps 62 and printed through the lens 63 on to a blue sensitive emulsion 64 on a support which carries on the rear side an antihalation layer 65 overcoated with a slow red-sensitive layer 66. The antihalation material may be included in the layer 66. A negative image is developed in the layer 64, the antihalation dye being removed, the layer 66 is exposed through the negative 64 by red light, and development and further processing continued. The masked negative, with the mask facing the light, is contact printed on to further material. The antihalation layer may contain equal parts of a blue-absorbing due such as bis - (1 -p -sulphophenyl - 3 -methyl - 5 -pyrazolone - 4)-methine oxonol or (3-ethyl-2-benzoxazole)- (1 - ethyl - 2 : 5 - dimethyl - 3 - pyrrole) - dimeth ine - cyanine chloride, a green-absorbing dye such as bis - (1 -p - sulphophenyl - 3 - methyl - 5 - pyrazo - lone-4)-trimethine oxonol or acid fuchsin, and a red absorbing dye such as bis-(1-p-sulphophenyl-3-methyl-5-pyrazolone-4)-pentamethine oxonol or the dye obtained by oxidizing 4: 4<1>- tetramethyldiamino - 4<11> - methoxytriphenyl - methane-3<11>-sulphonic acid. A half-tone negative or positive on material having on the opposite side of the support a sensitive layer may be exposed with four lamps so located that four dark spots are produced in the masking layer for each light spot in the original, the dark spots in the mask being located behind dark spots in the original. The dot elements are thus not masked by complementary light values although there is overall masking of the whole record by complementary light values. The four lamps may be replaced by four successive exposures, the mask being produced with the original and combined sensitive layer located on a turntable. Specifications 529,440 and 579,239 are referred to.