GB725737A - Process for intensifying silver photographic images - Google Patents

Abstract

725,737. Intensifying photographic images. DU PONT DE NEMOURS & CO., E. I. May 11, 1953 [July 17, 1952], No. 13106/63. Class 98 (2). Photographic silver images are intensified by treatment with an aqueous solution containing ferricyanide ions and ions of lead, zinc, mercury, copper, nickel, cobalt or cadmium, followed by toning in an aqueous solution containing chromate or dichromate ions and at least one polyvalent metal cation which forms a waterinsoluble ferrocyanide. Alkali metal or ammonium ferricyanides may be employed in the first solution and the second solution may also contain ferricyanide. The preferred cation for the first solution is lead, and this may be supplied by lead nitrate, acetate, bromide, chloride, formate, lactate or citrate. The first solution may also contain an acid such as acetic, formic, hydrochloric, citric, nitric, glycollic or lactic acids, and also an alkali metal or ammonium halide. Buffering salts such as alkali metal acetates, formates, lactates and citrates may be added to keep the pH in the range 1-6. The preferred cations for the second solution are ferric and uranyl, but cations such as Va++, Cu<SP>++</SP>, Ag<SP>+</SP>, Co<SP>++</SP>, Mm<SP>++</SP>, Hg<SP>++</SP>, or Ni++ may also be used, and the chromate or dichromate may be potassium dichromate, sodium and ammonium chromates and dichromates or mixtures of these. For colour work, separation negatives may be obtained from a tripack comprising a very low coating weight blue record film in front of a bipack of green and red record films. After processing, the front film is stripped and intensified according to the invention. In an example, a colour film comprises a cellulose triacetate base, a red-sensitive, greeninsensitive emulsion containing a water-soluble yellow filter dye, a stripping layer composed of a mixture of 88 per cent hydrolysed and 99 per cent hydrolysed polyvinyl acetate, a greensensitive emulsion, a stripping layer of 88 per cent hydrolysed polyvinyl acetate and a low coating weight blue-sensitive emulsion. The yellow filter dye may be 4: 4<SP>1</SP>-methyl-bis- [1 - (p - sulphophenyl) - 3 - methyl - pyrazolone - 5] or 4: 4<SP>1</SP> - methenyl - bis - [1 - (p - carboxy - phenyl) - 3 - methyl - pyrazolone - 5]. After exposure and wetting with water, the blue and green record films are transferred to separate blank films and all three records processed. The weak silver image in the blue record layer is bleached in an aqueous solution comprising acetic acid, lead nitrate, potassium ferricyanide and potassium bromide and then toned in an aqueous solution of ferric nitrate, potassium dichromate and potassium ferricyanide. To neutralize somewhat the green colour of the intensified image, the final wash water may contain a dye such as Anthraquinone Rubine R cone. (C.I. 1091), Pontacyl Carmine 6B Extra cone. (C.I. 57) or Pontacyl Rubine Extra cone. (C.I. 179). Specifications 444,773, 552,230 and 629,631 and U.S.A. Specifications 2,274,782, 2,415,442 and 2,448,552 are referred to.