GB531243A - Improvements in gelatino silver halide photographic elements - Google Patents

Abstract

531,243. Photographic plates. KODAK, Ltd., SOPER, A. K., and STEVENS, G. W. W. March 27, 1939, No. 9477. [Class 98 (ii)] A sensitive glass plate useful in copying documents such as line drawings when subsequent hand engraving of the image-bearing layer may be necessary comprises a homogeneous gelatino-silver-halide layer of thickness between 2Á and 7Á when dry and a ratio of silver halide to gelatin between 2:1 and 5:1, or of thickness between 1Á and 5Á and a ratio of silver halide to gelatin between 2:1 and 5:1, and a gamma and maximum developable density each not less than 2.5. Preferable values are, thickness between 5Á and 3Á, silver halide to gelatin ratio between 2:1 and 3.5:1, and gamma and maximum developable density each not less than 3.5. Four specific examples are given. The layer may be of process emulsion, and may be optically sensitized, and have anti-halation provision such as an anti-halation layer on the back or between the layer and the support. After exposure and development, a varnish layer may be applied before engraving e.g. a negative varnish, and in particular cellulose nitrate dissolved in amyl acetate. The emulsion may be initially prepared with the desired ratio of silver halide to gelatin ; or it may be prepared with more gelatin than is required, and the ratio subsequently adjusted. The viscosity of the emulsion may be adjusted by precipitation with alcohol and re-dispersion in water to facilitate coating. The gamma and maximum developable density are determined from density measurements made on an element exposed in a time-scale sensitometer to light of intensity 28 metre-candles and colour temperature 2700‹K given by a tungsten lamp and developed for three minutes at 70‹ F. in a caustic-hydroquinone developer of stated composition. Specifications 428,382, 434,873 and 517,628 are referred to.