US2675313A

US2675313A - Photographic reproduction process

Info

Publication number: US2675313A
Application number: US267446A
Authority: US
Inventors: Henry C Yutzy; Edward C Yackel
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1947-11-04
Filing date: 1952-01-21
Publication date: 1954-04-13
Anticipated expiration: 1971-04-13
Also published as: GB655273A; FR980401A; BE517064A; DE874704C; BE517066A; GB725667A; US2596756A; FR980399A; FR1089934A; GB655274A; BE485609A; FR1092963A; DE927307C; US2763553A; US2592368A; GB726543A; BE485611A

Description

April 13, 1954 c. YUTZY ET AL 2,675,313

PHOTOGRAPHIC REPRODUCTION PROCESS Filed Jan. 21, 1952 SUBJECT LIGHT ALKAL/ AND DESENS/T/ZER UNHARDE/VED A gX EMULSION comm/Mme DEVELOP/N6 AGENT A LKAL/ DESEMS'ITYZE R 'IIIIA "IIIII 7 as,

HenryC'. Yaizy L Eduarda Yackel IN V EN TORS An'xami'z Patented Apr. 13, 1954 UNITED STATES P e-rear" GEE-316E" PHOTOGRAPHIC REPRODUCTION-PROCESS Henry-CiYutzy and Edward (3,"Yaokel, BQchestefn,

N. Y.-, assignors to- Eastman Kodak 'C6mpany,; Rochester, Ni 'YF, a corporation of Nejw J e'rsey Application January. 2-1, 1952,;Serial-No.-2 673461 10 Claims, 1

This invention relates to phSJtognaphy t and: r

particularly, to a photographic copy method for use-in the. reproduction of printedimatter.

There are a number of well-knownphotm graphic methods; of reproducing designs. such; as printed matter cn-paperor-other; supports. For instance, bythe so-calledreflex copylmethod an emulsion layer is exposed through, its. support and the printed matter ,isreproduced as alnegative orr-onemay print a negative andapositive-vtherefrom; by conventional;.methodas In thBwPhQtO mechanical art a common practice is to expose a suitable photographic element =sueh-as --a tissue and to transfer the exposed element to-ametal plate after which the unexposed emulsion is washed off th plate or thewashing offi may0c cur before transfer ofthe resist to-the plate: Similarly, in the Pinatype process after forming a hardened image, colored matter is printedfrom the .unhardened area, of the 7, element but, the. colloid vehicle is not transferred iromthat area to the printing surface. Ailimited amount of endeavor which apparentlyhas ,notbeen successful has been directed toa process wherein,

after exposing a dichromatedalbumen element,

the unexposed andunhardenedportionof the element is transferred to ,a second/support,

Inthe Yutzy et a1. U. "S patent application,

Serial No. 783,914 filed November 4, 1947," now;

U. S;Patent 2,596,756granted May l3; 1952,, is described a simple photographic methodinclud-f ing differentially hardeningsilver salt emulsion layers and transferring unhardened j strata ,of such layers to a support toobta-in pusefuliimages.

In that process, a substantially ,unhardened colloid-silver halide emulsion layer, preferably con,-, taming a colloid tanning silver halide developing agent, is exposed to a two-tone subject (line or half tone, subject). andgaiter development [in the presenceol. alkalLa stratum of 'thennexposed region. of the emulsiontlayer is;transferred-Jto receiving sheet by merelypressing the sheet into contact with the developed emulsion layer and peeling off the sheet carrying a stratumof the unexposed region of the emulsion adhered thereto. Theisimplicity, of theprocessis ap fi when the. comparison is made; with, well-known, reproduction methods such, as those employing metal printingv plates which, involve tedious etching steps .for the preparation of the printing form, Other advantag6S residejintheiact that the silver halide, sensitized lmaterials-are. em.-.

ployed the superionproperties of which,.,,are wellv known compared to elements. sensitiaed,,by,othe g means, such eel bichromated .icolloid. layers;

21 In, theqmentionedrproeesstWit isgdesirable mthatthenstratumnof,emulsions obtained on the receive i ing. sheet, have sufiicient, opticaldensity,thatdt is readily visible. Tothat end, colored-matter? was;

either initially incorporated ,into Tthe, semulsion-r layerbefor exposure or. SIlbSBQHQHHML 'GiSQfOLmEQi in. the emulsion, layer; fort-exemplarbyrexposure 1 of ,the. transferred.stratum-of,emulsion.totlight; followedby, heating; if ,desireds,ato-raccelerate del velopment of. the silver, halide in, rthe r-stratumi Also, the invention described incorporating thgz r components/of color:forming deuelppmentsornof the. vdiazo process into-the emulsionday errtoeform=-. a dye image therein;ionwpurmSeeofsintensifyingI;1

,the transferred ,straturn, In; addition; the :men:

tioned process was essentially a darkroonrproe ess, inasmuch, as the, developed r-,emulsien=, layer possessed.nnhardenedvemulsionregions con-tear 1;-v ing developing agent and alkali associated with I the unexposed silver halidetand since premature commercial" application; some; economical method 'had to be provided to enable the-use 'of high speed silver halide emulsions inrelativelysimple processing equipment with a maximum;amount of the processing being"carriedoutnnder room,

, lights.

The objects of our invention are to provide improvements in th'e mentioned photomechanic'al copy method which satisfy the mentioned need for an eflicacious process of obtaining "copy hav inggood-optical density-andpreferablypymeans of "a process; the greater "partfof; which can. be carried out underprdinary flconditions oi;i1lumi nation.

In general; the, gobi ects of our invention are 3611.,

* meli h dby ce rins outtliem n n expo-a redev nment an tr nsf rsteps ut atisomfi =1 stage between therexposure, and transfen stepsa treating the,,,.exposed ,emulsion layen to increaser theuoptical density of.,the=unexpos:ed portions: corresponding., to-.the shadows ofl-thetoriginallsuh;

ject. Thiswtreatment, =preierably, inc ludes treat the,remulsionlayen sqme time following, x posurepwith arcomneund lwhichreactslwit he:

silver halide in; theflunexposedtlr ion :oir that:

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 and afte'r'devel'opment and prior to the transfer step, to treat" the developed emulsion layer with a material such as a compound containing a sulfur 'atoin' 'reac tive 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, developmentand 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 providecopy 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 draw mgs:

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 twotone subject.

The following detailed example is given to il1ustrate the preferred embodiments of our invention:

Example v A projection speed emulsion is prepared as described in detail in Example 1*of the mentioned Yutzy et a1. application containing 3,4

diphydroxy 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 BWD (copper phthalocyanine dye) or other insoluble pigments imparting some optical density to the emulsion layer but generally providing an insufficient amountof optical density to interfere with ex posure 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 is is the support for the emulsion such as celluloseester film base or preferably paper containing no agent tending to harden the emulsion. Layer ll represents the emulsion layer containing the tanning development agent. The emulsion layer II is. exposedtoasuitable subject l2 as shown in the drawings by any suitable projection means with the result. that 'a latent imageisobtained only in the silver halide in areas laof emulsion layer. I I. To obtain the optimum results, the exposure should .be adjusted so that little or. no latent image is ob-.

tained in regions other than 13. Exposure may be carried out by well-known reflex copy methods but is obviously not very satisfactoryif the,

emulsion contains colored pigment. Exposure. by, the reflex copy method is preferably carriedout by useof materials and methodswhich will be,

described in more detail hereinafter in 1 .1

tion with the methods of the Yutzy and Yackel patent application, Serial No. 267,447, filed concurrently herewith.

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:

4 f I 2 Per cent Sodium carbonate 4 Urea 10 Potassium bromide; 6.1

Development can be carried out at a temperature of from to F. for from 15 to 30 sec onds toobtain satisfactory results. Potassium bromide is used as the desensitizer in this exarnple 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. 0th" er desensitizers, such as desensitizing dyes, when used in the alkaline solution are employed in amounts 'in proportion'to their activity as desensitizers. Typical desensiti zing compounds are:

Pinakryptol Green Pinakryptol Yellow I 2-(p-diethylaminophenyliminornethyl) B-meth yl' quinoline methochloride -nitro-(i-chlorobenzotriazole 6-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 5 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 mate-- rial 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 fol" lowing development in concentrations of the order of from about 2 to 20 percent to ace-amino date. variations which may be encountered with different emulsions and condiitons of development.

'At'this stage in the process the developed element appears substantially as shown in the sec-- 0nd stage of the drawings wherein the emulsion layer II is shown as containing a tanned gelatin and silver image in regions l6 and the substantially unhardened emulsion and desensitized silver halide in the unexposed region is. V

The balance of the process may now be carriedout 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 compoundhaving a sulfur atom reactive with the silver halide in the unexposeddroxy diphenyl, 2,5-dihydroxy diphenyl, 5,63,8- tetrahydronaphthohydroquinone, and 2,3-dihydroxy diphenyl. The mentioned diphenyl compounds'are preferred. because they possess the combination of the common properties, high rate of development, high tanning efficiency, and solubility in the preferred range. Here, and. in the appended claims, where the tanning developing agents are 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 hydroquinone and pyrocatechol, in absence of sulfite, are used, they are less desirable but useful results may be obtained. Compounds like 2-hydroxy-5-amino 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 to a subject the differential hardening of the exposed emulsion can take place in the presence of a'tanning developing agent and that this includes whether or not the agent is in the emulsion before exposure.

When the tanning developing agent is employed in the alkalin developing solution rather than in the emulsion layer, this solution may also contain the desensitizing compound but it is preferred to utilize an intensifier in a subsequent operation rather than employing it together with the tanning developing agent in the alkalin developing solution.

As mentioned, the emulsion layers of our invention preferably contain a tanning developing agent but very desirable results are obtained by the use of a mixture of tannin and feebly tanning or nontanning developing agents such as described in the Yutzy andYackel application,

a Serial No. 267,447 filed herewith. Such emulsion agents are self-coupling in alkalin solution and thus yield colored images during development.

The following nontanning colloid silver halide developing agents are preferably used in the alkalin developing solution, the emulsion containing a tanning developing agent, at not greaterthan the indicated concentrations to insure that the nontanm'ng developing agent does not unduly compete with the tanning developing agent.

g./liter 2,4-diamino phenol 1.6 5-amino-2-hydroxy toluene sulfate 1.6 2,5-diamino toluene sulfate l- 1.6 p-Phenylenediamine 0.3 p-Aminophenol 1.6 p-Methylamino phenol sulfate 3.2 Isa-ascorbic acid 3.2

Emulsions containing mixtures of the two types of developing agents are utilized in our process, for example, as set forth in detail in the example above. The desensitizing and intensifying operations are likewise employed 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 differentially tanned with silver halide developing agents can be used, for example, polyvinyl alcohol, polyacrylamide and partially hydrolyzed polyvinyl esters. V

A particularly valuable modification of our invention includes exposing the substantially unhardened emulsion layer preferably containing a tanning developing agent, followed by development with an alkaline solution preferably containing one of the mentioned silver halide desensitizing agents, such as one containing 4% sodium carbonate and 0.1% potassium bromide. The developed emulsion is then treated with an alkali metal sulfite solution containing an intensifying agent such as an aqueous solution containing 4% sodium carbonate, 2% sodium sulfite, 10% urea and about 0.1% thiourea or other intensifying agent mentioned above such as thiosemicarbazide, arsenite, stannite, etc. The result is to develop a black silver image in'the unexposed region of the emulsion layer 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 solution. In this procedure it is not necessary to uniformly expose the emulsion prior to use of the sulfite solution 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 in this 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.

This application is a continuation-in-part of our application Serial No. 783,914 filed November 4, 1947 now U. S. Patent 2,596,756 granted May 13, 1952.

What we claim is:

1.. 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 aqueous alkaline solution of an alkali metal sulfite to retard hardening of the emulsion in the unexposed region, fogging said unexposed emulsionregion at some stage not earlier than said treating step, to initiate development, pressing a sheet having an absorbent'surface against said emulsion layer while the "layer is moist to cause only the said unexposed region ofemulsionto'adhere to said sheet, and separating said sheet and emulsion layer to transfer only astratum of the unexposed region or the emulsion layer containing silver to said sheet.

2. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-si lver halide emulsion layer containing a gelatin tanning snver halide developing agent, said emulsion being not harder than a gelatin layer containing 057 gram of formaldehyde per pound oig elatin :f-reshly coated, developing the exposedemulsion layer w th an alkaline solution to obtain a hardened gelatin and silver image in the region ef exposure and substantially unhardened gelatm and silver halide in the unexposed region of the emulsion layer, treating the developed emulsion layer with an aqueous alkaline solution containing sufiioient alkali metal sulfite :to retard hardening :of the emulsion in the unexposed region and :a-su-fiicient amount of a compound which :fogs silver halide in the absence of light .to initiate development of the silver halide in the unexposed region, pressing a sheet having an absorbent surface :against .said emulsion layer while the layer is :moist to cause only the said unexposed region :to adhere to said sheet, and separatingsaidsheet and emulsion layer to transfer only i8, stratum of th uno exposed region of the emulsion layer containing silver to said sheet.

A method of photographic reproduction which comprises exposing 1101a, two-tone subject a substantially unhardenedigel-atinoesilverlhalide emulsion layer containing ,a gelatin itanning silver halide developing agent, .said emulsion being not harder than .a gelatin layer zcont'aini-ng 19.7 gram of formaldehyde ,per mound of gelatin freshly coated, developing the -exposedrermilsion layer with an alkalinelsolutionatorobtainla hardened gelatin and silver image in the aregion of exposure and substantially unhardened gelatin and silver halide in the unexposed erosion or the emulsion layer, treating the developed emulsion layer with an-aqueous alkaline solution containing sufficient alkali :metalsulfite to retard hard ening or" the emulsion in the unexposed region and a sufficient amount of -a compound of the group consisting of thiourea, thiosemicarbazide, alkali metal stannites, alkali metal arSBHitesZhydrazine hydrate and aminoguanidine sulfate to initiate development of th lsillver halide in the unexposed region, pressing asheet havingan absorbent surface againstsaid-emulsion layer while the layer is moist to cause only the 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 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 aqueous alkaline solution containing sufficient alkali metal sulfite to retard hardening of the emulsion in the-unexposed region and sumcient thiourea to initiate development of the silver halide in the unexposed region, pressing a sheet having an absorbent surface against said emulsion layer While the layer is moist to cause only the said unexposed region to adhere to said "sheet, and separating said sheet and emulsion layer totransfer only a stratum of the unexposed region of the emulsion layer containing silver to said-sheet.

5. A method of photographic reproduction which comprises exposing to a two-tone subject a substantially unhardened gelatino-silver hali'de emulsion layer containing a gelatin tanning silver halide developing agent, said emulsion being not harder than -a gelatin layer containing D1 7 'g mm oi formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkalinesolution containing a dersensiti-zing agent for silver halide to obtain a hardened gelatin and -silver image in the region or exposure and substantially unhardened gelatin and silver halideiof reduced light-sensitivity in the unexposed region of the emulsion layer, -treating the developed emulsion layer with an aqueous alkaline solution of an alkali metal sulfite :to retard hardening :of the emulsion in the unexposed a egion, fogging .said unexposed emulsion regionat some stage not earlier than said treatingstepxto initiate development, pressing a sheet having an :absorbent lsurface against said aemulsion layer while the layer is moist to cause only the :said unexposed .reg on of emulsion to adhere to :said sheet, and separating said sheet -.and emulsion:layer.t0 transfer only a stratum of the-unexposedregion of the emulsion layer containing silver to, saidsheet.

",6. .lA method ;of ephotographic reproduction which comprises exposing :to ,a two-tone subject iasubstantially nnhardened gelatino-silver halide emulsion:layerrcontaining a gelatin tanning silver halide ,dcyfiloping agent, said emulsion being not harder than a gelatin,layercontaining 0.7 gram oi formaldehydeaper pound (of gelatin freshly coated, developing the exposed emulsion layer with an 3 :alkalineeolution containing a desensitizing agent :for silver, halide tonobtaina hardened gelatin and eilvergimageiin the-regional exposure and substantially unhardened gelatin and silver halide .of reduced light-sensitivity in the unexposed reeionlof the emulsionl-ayer, treating the developed emulsion layer with an aqueous alkaline solution containin ,suificientalkali ,metal sulfiteto retard hardening of the emulsion "in the unexposed resion and -suificient thionrea :to initiate development pf 513118 lsilyer lehalirle :in :the unexposed region, pressing a sheet having an absorbent surface against said emulsion layer While the layer is moist to cause only the said unexposed region of emulsion 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.

7-. 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 containing potassium bromide as a desensitizing agent for silver halide to obtain a hardened gelatin and silver image in the region of exposure and substantially una sam ihardened gelatin and silver halide of reduced light-sensitivityin the unexposed region of the emulsion layer, treating the developed emulsion layer with an aqueous alkaline solution containing sufiicient alkali metal sulfite to retard hardening of the emulsion in the unexposed region and sufficient thiourea to initiate development of the silver halide-in the unexposed region, pressing a sheet having an absorbent surface against said emulsion layer while the layer is moist to cause only the said unexposed region of emulsion 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.

'8. 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 of the group consisting of -3,4dihydroxy 1diphenyl, 2,5-dihydroxy diphenyl and 2,3-dihydroxy diphenyl, said emulsion beingnot 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 containing potassium bromide as a desensitizing agent for silver halide toiobtain ahardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide of reduced light-sensitivityinthe unexposed region of the emulsion layer, treatingthe developed emulsion layer withan aqueous alkaline solution'containing suflicient alkalimetal sulfite to retard hardening of the emulsionlin thelunexposed region and sufficient .thiourea to initiate developement of the silver halide in' the unexposed region, pressing a sheet having an absorbent surface againstsaid emulsion, layer while the layer is moist to cause .only the said unexposed region .of emulsion to adhere to sai'd'sheet, and separating said sheet and emulsion layer to transfer only a stratum of the unexposedreg'ion of the emulsion layer containing silver toisaid sheet.

9. 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 harderithan a gelatin'layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing the exposed emulsion layer with an alkaline solution containing a desensitizing agent for silver halide to obtain a hardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide of reduced light-sensitivity in the unexposed region of the emulsion layer, treating the developed emulsion layer with an aqeuous alkaline solution of an alkali metal sulfite to retard hardening of the emulsion layer in the unexposed region, uniformly exposing said emulsion layer to light, allowing the silver halide in the newly exposed region of the emulsion layer to develop in the presence of the sulfite solution, pressing a sheet having an absorbent surface against said emulsion layer while the layer is moist to cause only the said unexposed region of emulsion 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.

10. 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 V coated, developing the exposed emulsion layer with an alkaline solution containing potassium bromide as a desensitizing agent for silver halide to obtain a hardened gelatin and silver image in the region of exposure and substantially unhardened gelatin and silver halide of reduced lightsensitivity in the unexposed region of the emulsion layer, treating the developed emulsion layer with an aqueous alkaline solution of an alkali metal sulfite to retard hardening of the emulsion layer in the unexposed region, uniformly exposing said emulsion layer to light, allowing the silverhalide in the newly exposed region of the emulsion layer to develop in the presence of the sulfite solution, pressing a sheet having an absorbent surface against said emulsion layer while the layer is moist to cause only the said unexposed region of emulsion 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.

References Cited in the file of this patent UNITED STATES PATENTS Number I Name Date 2,596,756 Ylltzy et a1. May 13, 1952 FOREIGN PATENTS Number Country Date 204,101 Great Britain Sept. 17, 1925

Claims

1. 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 AQUEOUS ALKALINE SOLUTION OF AN ALKALI METAL SULFITE TO RETARD HARDENING OF THE EMULSION IN THE UNEXPOSED REGION, FOGGING SAID UNEXPOSED EMULSION REGION AT SOME STAGE NOT EARLIER THAN SAID TREATING STEP, TO INITIATE DEVELOPMENT, PRESSING A SHEET HAVING AN ABSORBENT SURFACE AGAINST SAID EMULSION LAYER WHILE THE LAYER IS MOIST TO CAUSE ONLY THE SAID UNEXPOSED REGION OF EMULSION 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.