GB777181A - Improvements in photographic sensitive materials - Google Patents

Abstract

777,181. Photographic emulsions. KODAK, Ltd. June 14, 1955 [June 29, 1954], No. 17104/55. Class 98(2) A photographic emulsion which is highly susceptible to Clayden desensitization is prepared by adding in a period of from 2 to 10 minutes an aqueous solution of a water-soluble silver salt such as silver nitrate to an aqueous gelatin solution containing at least 0.5 moles of a water-soluble chloride per mole of silver with or without up to 0.1 moles of a water-soluble bromide per mole of silver, and adding after the commencement of the addition of silver salt an aqueous solution containing between 0.1 and 0.5 moles of a water-soluble bromide per mole of silver, and continuing such addition of water-soluble bromide at least until all the silver salt has been added, the total water-soluble bromide and chloride being in molar excess of the silver salt. The additions may be carried out at 50 to 95‹C., but preferably at about 70‹C. It is preferred to add the silver salt during six minutes and to add the bromide during the last five minutes of that time. After addition of the salts, the emulsion is preferably stirred at about 70‹C. for 10 minutes, more gelatin is then added and stirred for 4 minutes at about 70‹C. and the emulsion then cooled to 30‹C. Soluble salts are then removed by washing or by coagulating the emulsion with sodium sulphate, rinsing and redispersing in water. A sulphur sensitizer mav be added as described in Specification 235,211 [Class 98(ii)]. The susceptibility to Clayden desensitization may be further enhanced by adding a merocyanine or hemioxonol dye as described in Specification 773,388. Specification 699,659 also is referred to.