US2027271A - Production of negatives with photographic images thereon of enhanced quality - Google Patents

Abstract

431,384. Photographic processes ; photo - mechanical printing surfaces. FIELD, A. E., 113, Ashmore Road, Harrow Road, London. Dec. 7, 1933, No. 34497. [Class 98 (ii)] A negative more especially for use in the production of photomechanical printing-surfaces is subjected to the action of a bleaching re-agent to produce a photographic image of positive appearance, retouched, etched, or reduced by means of a silver halide solvent, and finally subjected to the action of a solution which blackens the silver salt image and re-converts the image to a negative image. The bleaching bath may comprise (1) iodine in an aqueous solution of potassium iodide, (2) potassium ferricyanide and potassium bromide, or (3) potassium permanganate acidified with acetic or hydrochloric acid. The retouching or etching may be effected with a potassium cyanide bath, the portions of the image not to be retouched being coated with cellulose varnish or litho crayon. Other silver halide solvents such as sodium thiosulphate, or potassium iodide may be employed. After bleaching with iodine solution, the excess is removed with a potassium hydroxide bath. After bleaching with potassium permanganate, stains are removed by treatment with a bath of potassium meta-bisulphite. After retouching with potassium cyanide, the scum is removed by treatment with dilute nitric or acetic acid. The re-blackening bath may comprise sodium sulphide, or a metolhydroquinone developer, or a mixture of sodium sulphide and a developer. After washing, the negative may be intensified with mercuric chloride, bromide or iodide, or a redeveloping and intensifying solution comprising adurol, citric acid, silver nitrate, nitric acid and water may be employed. The fixing solution for the original negative may include potassium iodide.

Description

iii a;

i applied.

Patented Jan. 7,

UNITED STATES PATE N-T' OFFICE PRODUCTION or NEGATIVES wrrn PHD-- TO GRAPHIC IMAGES HANCED QUALITY THEREON or EN- Arthur Ernest Eield, London, England No Drawing. Application June 1'], 1935, Serial No'. 27,125. In Great Britain December 7,1933

2 Claims. (CI. 95-88),

This invention relates to the production; from dry plates, paper, film or.- the like coated with photographic emulsions of the kind comprising silver light-sensitized materials, of negatives with photographic images thereonof considerably enhanced quality compared with that of the photographic images as originally formed on the negative by the usual methods of development Heretofore improvements in the quality of the photographic image on a negative by retouching,

fine etching or reducing operations applied directly to the negative as such have involved considerable difiiculties and frequently not enabled the desired result to. be'obtained owing to V the fact that alterations-or corrections in tone value are not clearly visible on the negative and can only be properly observed when a positive "is printed from the negative.

Further for use in the production of photo-- mechanical printing surfaces it has been usual first to prepare a 'diapositive from a continuous tone negative of the picture to be reproduced, to

retouch or etch the diap'os'itive so as to obtain a positive having the correct colour and tone values and then to produce from the retouched or corrected diapositive a contact negative from which latter fiat printing forms were produced.

' tone-printing values consists in subjecting the This method however has the disadvantage that three separate plates are involved therein.

The present invention has for its object to enable negatives with photographic images thereon of greatly improved quality to be obtained by operations carried out on one and the same plate,

film or the like in which-the retouching, fine etching or alteration of tone values is' eflected positive appearance to a negative image. The retcuched or tone-corrected negative so obtained may be used as su'chfor printing from, or, especially in the case when the negatives are to be employed for photo-mechanical work, their density may be improved'by subjecting them to an intensifying treatment with one of the usual known intensifiers with or without a re-developer. If desired the intensified negatives can be bleached again to a positive appearance, re-' touched or etched as may be required, re-converted to a negative and then again intensified,

' the whole process being repeated as desired in accordance with the final result thatit is desired to obtain and the purpose for which the final negative is intended.

- The most suitable bleaching agent for convverting the original negative ,into one of a positive appearance is a solution of iodine in an aqueous solution of potassium iodide but there may also be used one of the other well-known photographic bleachers, such as a solution of potassium ferricyanide and potassium bromide or an acid solution of potassium permanganate, such on anintermediately formed photographic image V of positive appearance, thus overcoming various disadvantages, such for instance as thoseabove mentioned, met with in previous methods that have been proposed .tor the improvement of the quality of photographic images on negatives. For this purpose according to the present invention a processof treating a negative to give a photographic image thereon having improved negative to the action of a solution ot a bleaching reagent so as to produce on the plate, film or the like a photographic image of positive appearance, then effecting the required retouching, etching or reducing by means ofa solvent solu-' tion for the silver halide salts in the emulsion, and finally subjecting the plate, film or the like to the action of a solution which blackens the silver salts image and re-converts the image of as a solution of potassium permanganate acidified with acetic or hydrochloric acid.

, It is to be understood that throughout the present specification and claims the expression ployed an aqueous solution of potassium cyanide,

any parts of the positive image which it is desired-to protect from theaction of the potassium cyanide or othersolvent for the silver halide salts being coated with anappropriatereducer-resisting agent such as a varnish,.as for example a cellulose varnish or lithe crayon.

. The followingis a'description 01' one methodoi carrying the present invention into eiIect:--

An exposed photographic dry plate is developed 50 in the usual manner, for example with known developing solutions such as hydroquinone-caustic or metol quinoL rinsed in water and fixed so as to produce anegative which, on subjection to the etching or reduction operation, will leave a clean 'image. A suitable fixing bath is for example one of the following known composition:

Sodium thiosulphate crysta1s- 2 lbs. I 5 Sodium bisulphite 4 02s.

Potassium iodide oz.

Water to make 1 gallon After the plate has been fixed and washed it is converted to one of a positive appearance by 10 bleaching it with a solution of iodine in potas-' sium iodide, for example a solution containing 88 'well washed with water and then immersed in an aqueous solution containing about 5 per cent of potassium meta-bisulphite so .as to remove permanganate stains. When the bleached plate has been well washed with the potassium hydroxide :or metabisulphite solution, as the case may be, -so as to, be quite clear from iodine stYreaks or permanganate stains, it is rinsed in water and dipped for a short time, for instance about 10 seconds at ordinary atmospheric temperature, in a silver halide solvent solution such as an aqueous solution of hypo (sodium thiosulphate), potassium iodide, potassium cyanide or other known reducers. After treatment in the dipping bath as just mentioned, whereby a clear image free from stains is ensured, the reduction or etching of water, the plate being rinsed well in water after which it may be dried or left damp as desired for the next step. If all parts of the image now have the required tone then the next'step is to re-convert the positive to a negative image 45 in the manner described in detail hereafter by treating the plate with a solution which blackens the silver salts image. On the other hand if, as is more frequently the case, a further reducingor etching action of certainparts of the image isrequired to produce alterations ,of tone, varnish or litho crayon or other-reducer-resisting agent is applied to those parts of the image which already have the required tone and that 55 it is desired to protect from the action of the reducing bath, comprising a solvent solution for the silver halide salts, to which the plate is next subjected. After .the plate has been treated where necessary by varnish or other reducer resisting agent it is washed and dipped for a short time, for example ten seconds, in an aqueous solution of potassium cyanide (for example a solution consisting of 5 parts of a ten-per-cent stock solution ofpotassium cyanide and 145 65 water) whereby the varnished parts of the image willnow stand out more prominently from the unvarnished portions'which latter become heavier in -tone as a result of the action of the reducing bath. The plate is then immediately washed'in 7 water to stop the reducing action of the potassium cyanide solution on the unvarnished portions of the plate. Plates may be varnished and I reduced as many times as required in order to obtain the desired effect, and differences in tonal 75 values may be corrected or emphasized as rev effect of the dipping bathis stopped by the action quired in accordance with the strength of the reducing bath and the time during which the plate is immersed thereinu The use of litho crayon instead of varnish as the reducer resisting agent ,gives an edge which is softer than that obtained by varnish. After the re-touching or etching of the plate has been completed the varnish or other reducer-resisting agent is removed by the aid of a suitable solvent, whereupon the plate is treated with a dilute acid solution, for example a dilute 10 solution of nitric (e. g. commercial nitric acid 3 parts, water 60 parts) or'acetic acid, for a short time, say about seconds, in order to remove from the plate the silver residue which is left as a scum. The plate is then washed with water 15 and the image thereonre-converted into a negative' image by blackening the silver salts image in a suitable solution such as an aqueous solution containing about 0.5 per cent sodium sulfor instance as metol hydroquinone (thorough blackening being assisted if need be by exposure to light), or a solution containing both sodium sulphide and a developer. After the negative image has thus been re-formed on the plate his again washed and, after drying, may, for certain kinds of work, be printed from without further treatment. Where the negative is to be used for photo-mechanical work and the like its density may be improved by treatment with known in- 3 tensifying agents such as mercuric chloride, bromide or iodide, or the contrast or stencil effect may be strengthened by the use of .a redeveloperintensifier mixture such as one comprising adurol 1%; parts, citric acid 1 part, water 80 parts mixed place of the adurol solution there may be em- 40 ployed solutions of other plate-developing chemicals such as hydroquinone or metol. When the negative under treatment is a half-tone plate the half-tone dots, which have been reduced in size by treatment with the reducerii. e. the silver halide solvent) are not restored to their original size by the subsequent treatment with the redeveloper-intensifler mixture although their density is increased, since in the present process the dot opacity increases more than dot size during the aforesaid treatment with the redeveloper-intensifier.. This enables the half-tone dots to be greatly reduced in size and yet brought to a substantially uniform density of the required degree, a result which has not been possible in the processes heretofore employed where on redevelopment the dot opacity does not increase more than dot' size. Thus by means of the method according to the present invention negatives can be produced showing increased contrast and density with little alteration to image size.

The negatives after intensification are then ready for use in photo-mechanical printing work.

If found necessary or desirable the plates after havingbeensubjected to re-development with the adurol and silver nitrate solution can be phide or a solutionbontaining a developer such 2? verted to a negative by blackening in the manner previously described,

By means of the present process negatives of greatly improved quality are obtained. By -ef-' fect'ing the re-touching on an image of positive app arance the re-touching, fine etching or re- 7 reproductions of very high quality. The finished negatives obtained by the present process may be printed from for use with bichromated glue, albumen, or gum, or' silver or other sensitive surfaces.

By use of the methods according to the present invention there can be obtained negatives which in their finished condition are of greater opacity than those produced by the methods heretofore usually employed with dry plates. Further there may be obtained by the present process stencillike negatives of better quality, especially for use in photo-lithographic work, than those heretofore produced; these stencil-like negatives produced by the present methods give machine plates of more durability than those made from fringed I dot negatives which have been retouched with dye or by other methods heretofore usually employed.

It is to be understood that the process according to the present invention is applicable not only to plates but equally to films or paper or other base materials fioated with a dried photographic emulsion, and t at in the appended claims the term plate is usedto denote any of the usual base materials (including glass plates, films or paper) coated with a dried photographic emulsion as just mentioned.

What I claim and.desire tosecure-by Letters Patent of the United States is:-

1; A process oftreating a negative so as to ob tain a photographic image thereon having improved tone-printing values, especially for use in photo-mechanical printing work; which process consists in subjecting a fixed negative to the 5 action of a first solution comprising a bleaching reagent which produces on the plate a silver halide photographic image of positive appearance, then treating the plate with a second solution that is a solvent for the silver halide so as to effect the requisite retouching on the positive image a without re-converting it to a negative image, and finally subjecting the plate to the action of a third solution which blackens the silver halide image thereby reconverting the image of positive appearance to a negative image;

2. A process of treating a negative to obtain a photographic image, thereon having improved tone printing values, especially for use in photomechanical printing work. which consists in first subjecting the negative to the action of a first solution comprising a bleaching reagent which produces on the plate a silver halide photographic image of positive appearance, second, applyin a protective coating to those parts of the image which already have the required tone, third, treating the plate with a solution of a solvent for the silver halide imageto eifect the requisite retouching on the positive image'wlthout reconverting it to a negative image, fourth, removing so said coating and fifth, finally subjecting the plate to the action of a solution which blackens the silver halide image thereby reconverting the image of positive appearance to a negative image.