Photomechanical emulsions containing rare-earth metal salts

Claim 1

IN A PROCESS OF PREPARING A PHOTOGRAPHIC IMAGE IN A PHOTOGRAPHIC GELATIN SILVER HALIDE EMULSION LAYER, CAPABLE OF FORMING, UPON EXPOSURE AND DEVELOPMENT IN AN INFECTIOUS TYPE DEVELOPER SOLUTION, CONTAINING IN AN AQUEOUS SOLUTION, HYDROQUINONE, AS THE SOLE DEVELOPING AGENT, A STRONG INORGANIC BASE AND A COMPOUND OF AN ALDEHYDE WITH A BISULFITE, A HIGH CONTRAST IMAGE OF THE TYPE SUITABLE FOR HALF-TONE REPRODUCTION AS DISTINGUISHED FROM MEDIUM AND LOW CONTRAST EMULSIONS AND HAVING A GAMMA HIGHER THAN 5.0 WHEN DEVELOPED IN SAID DEVELOPER, WHICH INCLUDES PREPARING SAID EMULSION BY MIXING AN AQUEOUS SILVER NITRATE SOLUTION WITH AN AQUEOUS ALKALI HALIDE SOLUTION HAVING AN IODIDE CONTENT CORRESPONDING TO LESS THAN 0.5 PERCENT OF IODINE BASED ON THE AMOUNT OF SILVER NITRATE USED IN THE PREPARATION OF THE EMULSION, IN THE PRESENCE OF GELATIN WHICH SERVES AS THE COLLOIDAL CARRIER MATERIAL, RIPENING, WASHING AND AFTER-RIPENING THE GELATIN EMULSION THUS FORMED, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE EMULSION AT A STAGE PRIOR TO THE AFTER-RIPENING STEP, A WATER-SOLUBLE RARE-EARTH METAL SALT SELECTED FROM THE GROUP WHICH CONSISTS OF THE WATER-SOLUBLE SALTS OF CERIUM, GADOLINIUM, LANTHANUM, NEODYMIUM, YTTRIUM AND SAMARIUM IN A CONCENTRATION RANGING FROM 0.75 GRAM TO 20.0 GRAMS OF RARE-EARTH METAL SALT PER 1,000 GRAMS OF SILVE NITRATE USED IN THE PREPARATION OF SAID EMULSION, THEREBY FURTHER INCREASING THE GAMMA AND SHORTENING THE TOE PORTION OF THE CHARACTERISTIC CURVE OF SAID EMULSION.