US2739890A

US2739890A - Photographic reproduction process

Info

Publication number: US2739890A
Application number: US402722A
Authority: US
Inventors: Henry C Yutzy; Edward C Yackel
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1952-01-21
Filing date: 1954-01-07
Publication date: 1956-03-27
Anticipated expiration: 1973-03-27

Description

March 27, 1956 H, c. YUTZY ETAL 2,739,890

PHOTOGRAPHIC REPRODUCTION PROCESS Original Filed Jan. 21, 1952 SUBJECT UNHARDENE D A X EMULS/O/V CONFIfil/NG DEVELOPING AGENT A L KAL DESENS/ 772 E R AND INTENSIF/ER TRANSFER IN ROOM LIGHT l TRANSFER //v ROOM LIGHT Henry C. Ya izg Edward C. Yackel INVENTORY wwymm ATTORNEY 6} AGENT 2,73 9,890 PHOTOGRAPEHC REPRODUCTIGN PRGCESS Henry C. Yutzy and Edward C. Yacirel, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation or New Jersey Original application January 21, 1952, No. 267,466,

now Patent No. 2,675,313, dated April 13, 1954. Divided and this application .ian'uary 7, 1954, Serial No. 402,722

6 Claims. (Cl. 95-5.6)

This application is a division of our U. S. patent application Serial No. 267,446, filed January 21, 1952, now U. S. Patent 2,675,313, granted April 13, 1954, which is a continuation-impart of our U. S. patent application Serial No. 783,914, filed November 4, 1947, now U. S. Patent 2,596,756.

This invention relates to photography and particularly to a photographic copy method for use in the reproduction of printed matter. I

There are a number of well-known photographic methods of reproducing designs such as printed matter on paper or other supports. For instance, by the so-called reflex copy method an emulsion layer is exposed through its support and the printed matter is reproduced as a negative, or one may print a negative and a positive there: from by conventional methods. In the photomechanical art a common practice is to expose a suitable photographic element such as a tissue and to transfer the exposed element to a metal plate after which the unexposed emulsion is washed off the plate or the washing off may occur before transfer of the resist to the plate. Similarly, in the Pinatype process after forming a hardened image, colored matter is printed from the unhardened area of the element but the colloid vehicle is not transferred from that area to the printing surface. A limited amount of endeavor which apparently has not been successful has been directed to a process wherein after exposing a dichromated albumen element, the unexposed and unhardened portion of the element is transferred to a second support;

In the Yutzy et al. U. S. patent application Serial No. 783,914, filed November 4, 1947, now U. S. Patent 2,596,756, granted May 13, 1952, is described a simple photographic method including differentially hardening silver salt emulsion layers and transferring unhardened strata of such layers to a support to obtain useful images; In that process, a substantially unhardened colloid-silver halide emulsion layer, preferably containing a colloid tanning silver halide developing agent, is exposed to a two tone subject (line or half-tone subject) and after development in the presence of alkali, a stratum of the unexposed region of the emulsion layer is transferred to a receiving sheet by merely pressing the sheet into contact with the developed emulsion layer and peeling off the sheet carrying a stratum of the unexposed region of the emulsion adhered thereto. The simplicity of the process is apparent when the comparison is made with well-knownreproduction methods such as those employing metal printing plates and which involve tedious etching steps for the preparation of the printing form. Other advantages reside in the fact that the silver halide sensitized materials are employed, the superior properties of which are Well known compared to elements sensitized by other means such as bichromated colloid layers.

In the mentioned process, it is desirable that the stratum of emulsion obtained on the receiving sheet have sulficient optical density that it is readily visible. To that end, colored matter was either initially incorporated into the emulsion layer before exposure or subsequently was formed in the emulsion layer; for example, by exposure tent" of the transferred stratum of emulsion to light followed by heating, if desired, to accelerate development of the silver halide in the stratum. Also, the invention described incorporating the components of color-forming development or of the diazo process into the emulsion layer to form a dye image therein for purpose of intensifying the transferred stratum. In addition, the mentioned process was essentially a darkroom process inasmuch as the developed emulsion layer possessed unhardened emulsion regions containing developing agent and alkali associated with the unexposed silver halide and since premature exposure of that region of the emulsion would cause tanning development to proceed and thus prevent transfer of an emulsion stratum from the desired regions. Accordingly, the amount of room light which could be toierated in the process was a function of the speed of the emulsion and unless the process was carried out in lighttight processing equipment, the operations had to be carried out under safelights. In ofiice copy work, for which the process finds great commercial application, some economical method had to be provided to enable the use of high speed silver halide emulsions in relatively simple processing equipment with a maximum amount of the processing being carried out under room lights.

The objects of our invention are to provide improvements in the mentioned photomechanical copy method which satisfy the mentioned need for an efiicacious process of obtaining copy having good optical density and preferably by means of a process, the greater part of which can be carried out under ordinary conditions of illumination.

In general, the objects of our invention are accomplished by carrying out the mentioned exposure, development and transfer steps but at some stage between the exposure and transfer steps treating the exposed emulsion layer to increase the optical density of the unexposed portions corresponding to the shadows of the original subject. This treatment preferably includes treating the emulsion layer some time following exposure with a compound which reacts with the silver halide in the unexposed region of the emulsion layer to form a substance having the desired optical density. Our objects are also accomplished by treating the exposed emulsion layer during or following development with a desensitizing agent for silver halide to materially reduce the light sensitivity of the silver halide in the unexposed regions of the emulsion layer. If desired, the desensitization and optical density increasing treatments may be carried out during the alkaline development step.

' In the preferred process of the invention, it is desirable but not necessary to incorporate a desensitizing agent for silver halide in the alkaline solution used for development andafter development and prior to the transfer step, to treat the developed emulsion layer with a material such as a compound containing a sulfur atom reactive with silver halide in the unexposed regions of the emulsion; for example, thiourea, to form silver sulfide in that region. As a consequence of the use of the desensitizer,

devopment and any subsequent steps in the process can be carried out under room lights and the silver sulfide image formed in the unexposed regions transfers along with the emulsion stratum during the transfer step to provide copy having good optical density. The objects of the invention can be accomplished in other Ways as will be apparent from consideration of the following detailed description of our invention and the drawings:

In the accompanying drawings are shown in greatly enlarged cross-sectional view, the appearance of a typical photographic element at various stages in the process of copying a two-tone subject.

Thefollowing detailed example is given to illustrate the preferred embodiments of our invention:

Example A projection speed emulsion is prepared as described in detail in Example 1 of the mentioned Yutzy et al. application containing 3,4-dihydroxy diphenyl as the tanning developing agent and preferably being pigmented with a material such as metallic silver, carbon black, or a dye such as Monastral Fast Blue 3WD (copper phthalocyanine dye) or other insoluble pigments imparting some optical density to the emulsion layer but generally providing an insuflicient amount of optical density to interfere with exposure to any great extent. When the dye is employed, a suitable quantity is 15 grams per mol of silver in the emulsion. The light-sensitive element thus prepared is shown in the first stage of the accompanying drawings wherein layer 10 is the support for the emulsion such as cellulose ester film base or preferably paper containing no agent tending to harden the emulsion. Layer 11 represents the emulsion layer containing the tanning development agent. The emulsion layer 11 is exposed to a suitable subject 12 as shown in the drawings by any suitable pro jection means with the result that a latent image is obtained only in the silver halide in areas 13 of emulsion layer 11. To obtain the optimum results, the exposure should be adjusted so that little or no latent image is obtained in regions other than 13. Exposure may be carried out by Well-known reflex copy methods but is obviously not very satisfactory if the emulsion contains colored pigment. Exposure by the reflex copy method is preferably carried out by use of materials and methods which will be described in more detail hereinafter in connection with the methods of the Yutzy and Yackel patent application Serial No. 267,447, filed January 21, 1952.

After exposure of the emulsion layer, as described, development is carried out in absence of light or under suitable safelights in an alkaline solution preferably containing a desensitizing agent for silver halide and which may contain a tanning developing agent if none has been incorporated in the emulsion layer. A suitable aqueous solution is as follows:

Development can be carried out at a temperature of from S to 85 F. for from 15 to 30 seconds to obtain satisfactory results. Potassium bromide is used as the desensitizer in this example and should be used in the quantity required to reduce the light sensitivity of the silver halide in the unexposed regions of the emulsion layer to the requisite level. The use of 0.05 to 1.0 percent of potassium bromide in the solution will allow use of ordinary room illumination in carrying out the remaining steps of the process. Other desensitizers, such as desensitizing dyes, when used in the alkaline solution are employed in amounts in proportion to their activity as desensitizers. Typical desensitizing compounds are:

Pinakryptol Green Pinakryptol Yellow 2-(p-diethylaminophenyliminomethyl)-6-methyl quinoline methochloride 4-nitro-o-chlorobenzotriazole -ethoxy 2 p-nitrostyryl-quinoline metho-p-toluenesulfonate Desensitizing dyes are adequately effective in the alkaline solution in concentrations of the order of 0.025 gram to grams per liter of solution. Urea or other gelatin softeners can be used as shown in the solution to facilitate subsequent transfer of the stratum of undeveloped emulsion. The quantity used, of course, depends upon the hardness of the emulsion at this stage of the process and, of course, the activity of the material as a gelatin softener.

Urea and other gelatin softeners such as formamide, ethylene chlorohydrin, and sodium nitrate can be used in the alkaline solution or in a separate solution following development in concentrations of the order of from about 2 to 20 percent to accommodate variations which may be encountered with different emulsions and conditions of development.

At this stage in the process the developed element appears substantially as shown in the second stage of the drawings wherein the emulsion layer 11 is shown as containing a tanned gelatin and silver image in regions 14 and the substantially unhardened emulsion and desensitized silver halide in the unexposed region 15.

The balance of the process may now be carried out under room lights. To this end, excess solution can be drained or squeegeed from the surface of the emulsion and the element then treated in an intensifying bath preferably containing a compound which reacts with the silver halide in the unexposed regions of the emulsion layer to form a substance having appreciable optical density. A satisfactory and preferred bath contains a compound having a sulfur atom reactive with the silver halide in the unexposed region 15 of layer 11 to form silver sulfide therein such as the following aqueous solution:

Percent Sodium carbonate 4 Thiourea 2 The quantity of thiourea in the bath is not especially critical and alkaline baths containing from about 0.5 to 5 percent thiourea give useful results. Other compounds of a similar nature, such as thiosemicarbazide and sodium sulfide may be used for the same purpose in similar quantity. in place of using a sulfur compound for increasing the optical density of the unexposed regions, solutions of compounds capable of reducing the desensitized silver halide to silver in the absence of a latent image may be used, such as 0.5 to 2 percent solutions of hydrazine hydrate, aminoguanidine sulfate, sodium arsenite, ferrous oxalate and stannite solutions.

The intensified element now appears as shown in the third stage of the drawings wherein layer 11 is shown as containing the intensified image in area 16 which r area is still unhardened.

After removing excess moisture from the emulsion surface of the intensified element as by squeegeeing, it is then pressed with the emulsion side next to an absorbent sheet or other surface such as paper 18 with the result that only the intensified and unhardened region 16 adheres to the sheet. When the sheets are separated only a thin stratum 17 of region 16 adheres to the sheet 18 as shown in the last stage of the drawings. Additional copies of the subject 12 can be made by merely remoistening the emulsion layer 11 with alkaline solution and transferring to sheets until the intensified and unhardened region 16 of layer 11 has been emausted. It is not necessary to further treat the copies obtained inasmuch as they are comparatively dry and the image thereon is stable.

In an alternate procedure after exposure of the sensitive element as shown in the first stage of the drawings, it may be treated directly with an alkaline solution containing both the silver halide desensitizer and the intensifying agent for the unexposed region of the emulsion layer. The result is to obtain an element appearing substantially as shown in enlarged cross-sectional view at the left of the drawings wherein region 19 of layer 11 comprises the unhardened emulsion region which has been intensified and region 14 desensitized. For this pur pose the alkaline solution may contain the indicated quantity and types of desensitizing agents, particularly a desensitizing dye, together with the compound reacting with silver halide in the unexposed region to increase the optical density. The following concentrations of the intensifying compounds may be used in the alkaline solution:

variations.

Mg; per liter r of solution -'S odiumsulfide 250 Thiourea "50 "Thiosemicarbazide 250 "Hydrazine hydrate (85% in water) 25 Aminoguanidine sulfate 500 The concentration of these ingredients can be-variedas much as about 50 percent to obtain useful results. Other agents which may be used in the alkaline developing solu- -.tion in similar concentration to reduce the silverhalide in the unexposed regions of the element -are,,arsenite,.stannite and ferrous oxalate compounds.

:When the intensifying agents are used in the alkaline solution as described and the emulsion contains artanning .silver. halide. developing agent, an unusual mechanism vbecomes-patent. That is, itwould be-supposedthat the reagent, such as thiourea, would react with all ofthesilver .halidein the emulsion layer, whether it has-beenexposed.

.or' not, and prevent differential tanning of-theemulsion layer. However, it appears that the diffusion rate of alkali .into the emulsion layer is greaterthan the diffusion-rate of the sulfur compound; consequently, development precedes' intensification as attested by the results. -Otherwise, it. appears thatthe results could possibly be explained by .development proceeding at a rategreater than intensification. When emulsion layers free of developing agents are treatedsimilarly, this .is not observed.

.- The process of ourinventionis subject to numerous The use of the desensitizingagent. in the developing solution is preferred; however, it .maypbe employed in a step, following developmentalone or. in conjunction with the intensifying. compound. .Also .the alkaline solution may contain the. intensifier and desensi- Itizing can be effected in a step following development. Similarly, as mentioned in our 'U. S. application Serial No..7 83,914, now U. S. Patent 2,596,756, granted May .13, 1952, the intensifying agent, suchv as thiourea, may be incorporated in the receiving sheet or if desiredzmay be. used for treating the transferred stratum of silverhalide emulsion.

"The concentration of developing agent in the emulsion is dependent in part upon the result desiredbut can be of theorder of 350 grams of developing agent per kg. of silver nitrate converted to silver halideused in making the. emulsion to obtain good-density, or about 250 grams per kg. of silver nitrate to obtain adequate density.and

an emulsion having optimumkeeping properties.

It is necessary for the successful operation ofthe invention'that the emulsion layer be not harder than would be the case with gelatin containing 0.25 oz. of formaldehyde, (40% diluted l.to 3 with water) or 0.7. gram dry formaldehyde per pound when freshly coated, or 0.1 oz. of the. solution per pound for a sample aged. three :tosix months. By substantially unhardened as used. here,-and .inthe. appended claims, it is to be understood "thatv this .means a hardness of the order obtained. with gelatin .treatedwith formaldehyde under theconditions above.

Emulsion layers appreciably harder will not transfer satisfactorily. :Similarly, if after development of the tanned image it is found that the layer is 'too hard, and to accom- .;modate variations inhardness and tanning encountered, wwecanuuse variations of temperature or'pressure when making a transfer. To this end we ordinarily apply pres- :.sure=or temperature or both when rolling the developed emulsion down onto the receiving support.

Examples of tanning developing agents especially useful because-of nonwandering characteristics in-emulsion layers are those having a solubility. at..20 C. of from about .005 to 1.0 gram per 100 cc. ofa phosphate-citric :acid-buffer solution of pH 5.0 prepared from a 1.5 percent solution ofsodium dihydrogenphosphate and sufficient citric acid to bring the pH to 5.0. The preferred edevelopingagents-have a solubility-offrom-about .01

6 --to 5.2 gram per- 100 ech of. buffer solution. Developing agentsfalling within the above classification are, for .exam- ---ple, 3,4-dihydroxy -diphenyl," 2",5 dihydroxy :tdi'phenyl, 5,6,'7,8 --tetrahydronaphthohydroquinone, :and" 2,3 dihy- 5 droxy diphenyl. "The-mentioned diphenyl compounds are preferred because" they possess the; combination of the --common properties -high rate of developmenhhigh' tanning- 'efliciency, and solubility in the preferred range. "Here,- and in the appended claims; where the tanning lof'developing agentsare mentioned as incorporated in the emulsion, the desired compounds are,- for, example; those :mentioned and -having the mentioned characteristics. "Otherwise, where tanning developing agents as' hydroquinoneand pyrocatechol, in absence of'sulfite, are used, =theyare less desirable but usefulresults may; be obtained.

Compoundslike Z-hydrox-y-S-am-ino "diphenyl or" 3,4- diamino diphenyl are not-especially useful because of their-poor stability or failure-to tan. It 'iS, therefore, apparent that after exposure toasubject the differential hardening of' 'theexposed emulsion can' take place .in .the .;presenceof a'tanning developing agent" and that this includes==whether or not the agent is in the'emulsion before exposure.

-When'thetanning developing agent is employed in the 'alkaline-developing solution-ratherthan in the' emulsion -layer,-"'this solution may also contaimthe desensitizing compound but it is preferred to utilize an intensifier in a subsequent operation rather than employing it together with thetanning' developing agent in the alkaline develop- -ing solution.

-Asmentioned, theuemulsion layers of -our.,invention preferably contain a tanning developing agent but very desirable results are obtainedby the use'of amixture of "tanning I and feebly tanning or-nontanning developing agents'such as described in the YutzyandYackel'application Serial No. 267,447, filed January'21,' 1952. Such -em ulsion layers are employed. advantageously 'when. exposures are to be made by--the reflex copy method. Sub- -stantia-lly nontanning silver halide developing agents satis- 40 .factoryforthis purpose are: N-methyl-p-aminophenol-x- ;.sulfonic 4 acid, p-hydroxy-anilino-methane sulfonic' acid, 1 pyrogallol dimethylether, 1:, 8 dihydroxy naphthalene and i 4-methoxy-1-naphthol. These developing agents are pref-' erably employed in emulsions along with about '60 to 65 -percent of the tanningdeveloping agents. The latter two developing agents are -s'elf-coupling in alkaline" solution and thus yield colored imagesduring development.

The following nontanning colloid silver halide developing agents are preferablyused'inthe alkaline developing solution, the emulsion containing atanning-developing agent, at not greater than the indicatedconcentrations to insure'that"thenontanningdeveloping agent-does not unduly compete with the tanning developing agent.

2,4'-'diamino-phenol 1.6 5amino-2.-hydroxy toluene sulfate 1.6 2,5-diamino toluene sulfate 1.6 p-Phenylenediamine 0.8

p-Amino'phenol 1.6 p-Methylamino phenol-sulfate 3.2 Isoascorbic acid 3.2

Emulsions containing mixtures of the two types-of developing agents are utilized in our .process,f for example, as set forth in detail in ,the example above. 'lThedesensitizing and intensifying operations arelikewise e ployed to facilitate handling under room-lights and. to

yield intensified copy of the original subject.

The colloid vehicle of, the silver halide emulsion layers used in our invention is preferably; gelatin although other "materials capable of being difl'erentiallytanned with silver halide developing agents can be .used', for example, poly: -'vinyl alcohol,- polyacrylamide and; partially; hydrolyzed poly viriylesters.

A particularly *valuabletmodificatmn of; our invention "in'cl-udes exposing the 'substantially unhardened emulsion Isolution. i'formly expose the emulsion prior to use of the sulfite soluavsaaeo 1 layer preferably containing a tanning developing agent, followed by development with an alkaline solution preferably containing one of the mentioned silver halide desensi-tizing agents, such as one containing 4% sodium carbonate and 0.1% potassium bromide. The developed Slayer and at the same time some silver sulfide may be obtained in that region, yet hardening of the gelatin in the region is retarded or suppressed by the sulfite in the In this procedure it is not necessary to unition since the intensifying compounds chemically fog and initiate development of the silver halide.

In a similar manner, after initial exposure to a subject of the emulsion layer containing tanning developing agent, the latent image can be developed in alkaline solution such as 4% sodium carbonate containing 0.1% potassium bromide, followed by treatment in alkaline sulfite solution to retard hardening such as 4% sodium carbonate, 2% sodium sulfite and 10% urea. After treatment inthis solution for a few seconds the emulsion is then uniformly exposed to light to render the newly exposed silver halide developable and non-tanning development of the emulsion proceeds with the formation of a black silver image in substantially unhardened gelatin in the shadow region of the emulsion. Of course, this and the process just above then entail transfer to an absorbent surface of a stratum of the shadow region of the emulsion the optical density of which has been'increased.

What we claim is:

l. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unlhardened gelatino-silver halideemulsion layer contain- :ing a gelatin tanning silver halide developing agent, said emulsion being notharder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide in the unexposed region of the emulsion layer, treating the developed emulsion .layer with a member of the class consisting of an alkaline solution of from about 0.5 to 5% of a compound having a sulfur atom reacting with silver halide to form silver sulfide, and an alkaline solution of from. about 0.5 to 2% I of a compound reducing silver halide to silver in the absence of a latent image, pressing a sheet having an absorbent surface against said emulsion layer while said emulsion layer is moist, to cause only said unexposed region to adhere to said sheet and separating said sheet 7 and emulsion layer to transfer only a stratum of the unexposed region of the emulsion layer to said sheet.

2. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent, said emulsion being not harder than a gelatin layer containing 0.7

' gram of formaldehyde per pound of gelatin freshly coated,

developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide in the unexposed region of the emulsion layer, treating the developed emulsion layer with an alkaline solution of from about 0.5 to 5% of a sulfur compound of the class consisting of thiourea, thiosemicarbazide and sodium sulfide until said unexposed silver halide has been converted to silver sulfide, pressing a sheet having an absorbent-surface against said emulsionlayer while said emulsion laye r is moist, to cause only said unexposed region to adhere to said sheet and separating said sheet and emulsion layer to transfer only a stratum of the unexposed region of the emulsion layer containing silver sulfide to said sheet. f

3. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent, said emulsion being not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide in the unexposed region of the emulsion layer, treating the developed emulsion layer with an alkaline solution of from about 0.5 to 2% of a compound reducing said silver halide to silver in the absence of a latent image, pressing a sheet havingan absorbent surface against said emulsion layer while said emulsion layer is moist, to cause only said unexposed region to adhere to said sheet and separating said sheet and emulsion layer to transfer only a stratum of the unexposed region of the emulsion layer containing silver to said sheet.

4. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent, said emulsion being not harder than a gelatin layer containing 0.7 gram'of formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver silver halide to form silver sulfide, pressing a sheet having an absorbent surface against said emulsion layer While said emulsion layer is moist, to cause only said unexposed region to adhere to said sheet and separating said sheet and emulsion layer to transfer only a stratum of the unexposed region of the emulsion layer containing silver sulfide to said sheet.

5. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent, said emulsion being not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the region of exposure and substantially'unhere to said sheet and separating said sheet and emulsion layer to transfer only a stratum of the unexposed region of the emulsion layer containing silver to said sheet.

6. The process of claim 2 wherein the sulfur compound used is thiourea.

References Cited in the file of this patent UNITED STATES PATENTS Yutzy et al. May 13, 1952 FOREIGN PATENTS zo rio'if" Great Britain a Sept. 1.1111925

Claims

1. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRIES EXPOSING TO A TWO-TONE SUBJECT A SUBSTANTIALLY UNHARDENED GELATINO-SILVER HALIDE EMULSION LAYER CONTAINING A GELATIN TANNING SILVER HALIDE DEVOLOPING AGENT, SAID EMULSION BEING NOT HARDER THAN A GELATIN LAYER CONTAINING 0.7 GRAM OF FORMALDEHYDE PER POUND OF GELATIN FRESHLY COATED, DEVELOPING THE EXPOSED EMULSION LAYER WITH AN ALKALINE SOLUTION TO OBTAIN A HARDENED GELATIN AND SILVER IMAGE IN THE REGION OF EXPOSURE AND SUBSTANTIALLY UNHARDENED GELATIN AND SILVER HALIDE IN THE UNEXPOSED REGION OF THE EMULSION LAYER, TREATING THE DEVELOPED EMULSION LAYER WITH A MEMBER OF THE CLASS CONSISTING OF AN ALKALINE SOLUTION OF FROM ABOUT 0.5 TO 5% OF A COMPOUND HAVING A SULFUR ATOM REACTING WITH SILVER HALIDE TO FORM SILVER