GB626053A - Improvements in sensitive photographic materials - Google Patents

Abstract

626,053. Photographic silver salt emulsions. KODAK, Ltd., TEAL, E. F., and DAVEY, E. P. April 1, 1946, No. 10022. [Class 98 (ii)] A developing-out silver salt emulsion is prepared by forming the sensitive silver salt in the presence of one or more of the following substances: arsenites (e.g. meta-arsenites), stannites, phosphites (e.g. meta- and hypophosphites), antimonites, hyposulphites and germanites. The emulsion may be of the ammoniacal or non-ammoniacal type, and may be a silver bromiodide or bromide emulsion. The emulsion may be coated immediately after ripening without washing, or may be washed and digested before coating. The emulsion may be an autopositive emulsion which is chemically fogged (e.g. with hydrazine, formaldehyde, hydroxylamine, or excess silver nitrate, or by extra digestion with or without sulphur sensitizers such as sodium thiosulphate), or light fogged. The substance may be added to the mixed halide solution used for forming the silver bromiodide emulsion, and the emulsion made in the usual manner using ammoniacal silver nitrate solution. With an autopositive emulsion, the formation of negative images on low exposure may be avoided by adding hydrazine hydrochloride or formaldehyde to the emulsion immediately after mixing the two solutions. The emulsion may be sensitized with sensitizing dyes, and a quantity of dye greater than the optimum may be used as in Specification 524,087. A developing agent such as hydroquinone may be added to the emulsion to permit of development merely by immersion in alkali, and the emulsion will thus be tanned imagewise, permitting the unhardened parts to be washed off.