US2130735A - Method of producing a printing plate - Google Patents

Description

Sept. 20, 1938. E. E. ECKARDT METHOD OF PRODUCING APRINTING PLATE 0;iginal Filed Nov. 18, 1933 INVENTOR 5w: faunko fez/mo?" A'TTORNEY atented Sept. 20, 1938 p g f 40 present in the individual portions of the image.

METHOD OF PRODUCING A mmme PLATE Emil Eduard Eckardt, Dresden, Germany"- Original application November 18, 1933, Serial No. 698,671. Divided and this application, February 20, 1937, Serial No. 126,933. In Germany December 12, 1932 6 Claims. 95-5.7)

This invention relates to photographic image My invention permits making negative or posibearers, such as plates or films, and to a method tive photographic pictures of any desiredv subof making and reproducing same, such as dejects (persons, articles, scenery, etc.) embodying scribed in my application, Serial No. 698,671, filed the natural screen referred to. From the originals November 18, 1933, of which application this is a copies such as image reproductions, printed re- 5 division.- productions or the like can be produced by any It is an object of my invention to prepare a well known methods of reproduction and printphotographic image bearer so as to facilitate its ing. reproduction and reduce its cost. To this end I It is known that by exposing a light-sensitive eliminate the necessity of using a separate screen silver-halide layer and by developing the exposed 10 a by treating the light-sensitive silver-halide layer layer, a silver image is produced which consists of the plate or film in such a. manner that the of blackened silver particles. A picture obtained silver particles in the layer itself will form a in this manner if positive (known as a lantern screen. slide) may be the final product, or a positive or A separate screen, produced according to one negative picture may be the original for reproofthe old methods and formed of lines interduction, such as phototype, plain printing, lettersecting at right angles is placed between the press printing, copper-plate printing, color printoriginal and a second plate on which the original ing, etc,

s p t g ap d. This necessity of making a In the reproduction of photographic pictures Se e d photograph increases, of Cou t 60 15 as heretofore performed it is possible only to 20 of the operation, and moreover the image or picobtain copies which substantially correspond to ture on the second plate is not altogether satisthe photographic shades of the original, which factory because the lines of the screen show inthe requires the separate screen referred to to be supic-ture, interfering with its contrasts and break- 'perlmposed on the picture. This is undesirable me up t p e by their regular strictly 'g eofor the reasons stated, and particularly if it is 25 etr c a a emen desired toobtain the effect of a line etching, for.

v The natural Screen formed according o he which normal photographic originals cannot be present invention, is, on the other hand, of an. used. V

irregular character. It may consist of continu-' This drawback I eliminate according t my 0115 curves of individual spots- A Screen of vention by forming the natural screen on the 30 s kind s Obviously preferable 110a regular 8 0-, original. With an original of this kind I.may metricscreen of 01d kind because it interobtain reproductions which resemble either a feres far less with'the contours of a photographic 1 1; m made by hand, or a half-tone repr picture than the straight intersecting lines of the a t From positive original havin the d Screen- Being P d in the Silver image natural. screen in the silver image of its silver- 35 of the layer itself, the natural screen adapts ithalide layer. 1 may btai printing plates for self to the various shades of the photographic plain d p erlate printing, offset printing image as its Properties are determined by the and phototype, and from a negative original havamount of blackened silver particles which are mg the natural screen I may obtain printing plates for book and newspaper printing. 40

According to this invention, the silver image (and the printing faces of the plates obtained The darkerportions obviously contain more such particles than the lighter ones, and the lightest portions may even befree from all silver parti- I cles, that is to say, they may b pure white or fromthe image) is selectively influenced and absolutely transparent. .The screen may not F t g from the 3 of h silvershow in those portions of the image which are hahde layer n during the Individual stages of absolutely black or pure white, but only in the the method so a desired effect of the shadings or half tones which are intermediate productions is obtainedthese extremes; a 1 The exposure may be so regulated that the lat- The efie t of photographs and particularly ent image obtained is most favorable for the 50 portraits, becomes more artistic by the natural 91 in VleW,v The p ent Of the latent screen, so that reproductions from such photoimage must be pe n ed such a manner that graphs, plates orfilms are not only more conthe blackened silver particles which are avail.- trasted than those obtained by the bid method, ble after the xp u are P p ly produced but bear a great resemblanceto engraving s. j and distributed The same applies to the fixing,

intensification, reduction, and covering (if any), of the layer.

The result is a dislocation and rearrangement of the blackened silver particles whereby the particles are crowded nearer together in certain places while being withdrawn from the regions in the vicinity of the points of local concentration. In this way the natural screen is formed. The blackened silver particles combine into curved lines or individual spots of black, which are bordered or surrounded by curves or areas of white.v

In the appended drawing, in which, by way of example, two kinds of natural screens are illustrated diagrammatically,

Fig. 1 shows a screen with black curved lines, while Fig. 2. shows a screen with black spots, both figures being magnified. 4

Fig. .3 is a magnified cross-section of an image bearer having two intermediate layers between the halide layer and the support of the layer, as will be described more in detail below.

I, I in Fig. 1 indicate the black curves or lines formed by the silver particles, with corresponding white liens or areas surrounding them, while 2, 2 in Fig. 2 indicate the black spots of silver particles described above. The plates were uniformly exposed to light for a short time. I

The dislocation and. re-arrangement of the silver particles and the variation or subdivision of the silver image producea very plastic effect in negatives, positive copies, and lantern slides. The irregularity of the lines or spots of dislocated sil- .ver particles, with their skeleton-like subdivision, produces an artistic effect resembling that of an engraving, without in any way interfering with the outlines and the effect of the. picture.

The variation of the silver image produced ac-,

cording to this invention is equivalent to the effect of a high-class'screen. The term screen as obviously eliminated. The photographic shade is formed exclusively by a rearrangement of the silver particles present in the layer.

The formation of the natural screen in the silver-halide layer comprises two stages:' the developing of an exposed layer and the softening or soaking of the-layen-to impart to it a jellylike character which permits the blackened silver particles to move or "float in the layer. The silver particles have a tendency to cluster as soon as they are free to move or fioat in the softened or soaked layer, and this tendency can be furthered by physical, thermal or chemical action mersed. The higher the temperature gradients,

the finer will be the screen. Such alternating baths may be applied before the development, be-

fore the fixation, and in particular after the application of the bath in which the screen is formed, 1. e., in which the gelatine forming the layer is softened. The developer and the fixing bath themselves may form parts of an alternating bath, 1. e., the developer or the fixing bath may be hot or cold, and the preceding or succeeding bath may be cold .or hot. It has proved favorable in certain cases to first place the layer in water or oil of about 25 C. before developing the layer, or to first subject the layer to the action of water vapor (steam).

The finest screens are obtained by thermal action, the layer being heated in dry condition to about 50 (3., or more, before being developed, so that its water content is partly or completely expelled. A layer which has been subjected to this preliminarydrying treatment, will stand baths, and more particularly developers, of rather high temperature, up to 50 C. and even above this temperature.

'It has been found that the natural screen forms more readily in layers which are comparatively hard and will stand temperatures of the order of 36 to 38 C., and that screens formed in such hard layers are more contrasted than screens formed in layers which new soft that they would melt and come off the glass or film when heated to such a high temperature range. Such softlayers however are very suitable for photographic reproduction, though not for printing. If reproduction by printing is desired, hard layers should used.

Plates or films may be subjected to the preliminary drying treatment before being sold. Such plates or films, in addition to their other desirable properties, will stand tropical temperatures as they will hardly be exposed to temperatures of 50? C. and more even in the Tropics.

As mentioned above, plates and films which have been dried by heating will withstand'the action of hot developing baths. High temperature of the developer is desirable as the period of exposure may be shorter, and as the temperature gradients in the case of alternating baths may be much higher, resulting, as has been stated above, in finer screens. With the shorter exposure period the silver-halide layer to be developed becomes thinner and this is favorable for the formation of the screens because only superficial development is required. This mode of development is preferable because the contrast between the dark lines of the screen and the white intermediate areas is increased. :With a concentrated and/or hot developer the developing period may ,be reduced to 30 seconds and less. Layers developed superficially have a more harmonious effect and are so thin and permeable to light that a successful exposure of the copy, for instance a metal printing plate to be etched, is insured.

Preferably, in the first water bath applied to the layer after it has been developed or fixed, the layer is slightly contacted with the water in the bath repeatedly, say, six to ten times, until the layer has become mat like velvet. This deprives the layer of its water-repellent character, particularly as regards hot water, so that the subsequent baths become more efficient. A similar operation may be performed in the screenforming bath, but only before the screenhas' if a warm developer is followed by a cold bathof ammonia, ether, or a mixture of both. In a screen obtained by such chemical treatment, the

silver particles do not break upthe contours of the picture into serrations but conserve them al-- most in unchanged condition. a

By these means a more or less contrasted coarseor fine screen can be obtained, as desired.-

hardening, by the fineness of thegelatine grain,

and by the size of the silver particles.

In order toobtain a satisfactory screen, it is necessary to try out at which temperature of the baths the :most favorable jelly-like condition of the layer is obtained, without the layer becomin detached from the support altogether.

The examples which will now be described, relate to fresh plates, or to plates which havenot been stored for a long time.

According to Figs. 1 and 2, thefdensity and blackness of the curves i or spots 2 are uniform because the plates were exposed to light without a picture being projected thereon. In the screen shown in Fig. 2 the formation of the screen was prematurely interrupted. The curves or lines in Fig. 1 are all connected but subjected to .a continuous change of direction.

The simplest method of producing a natural screen is the following:

An exposed and developed layer is placed in a bath of water having a temperature of say to 36 C. and left therein for ashort time, say one or two minutes, until the silver particles have clustered. Instead of the water bath, a bath of oil, such as olive oil, sun flower oil or the like may be used, or the layer may be subjected-to the action of water vapor. A plate or film which has been treated according to this simple method, may serve for use as a lantern slide, or for photo copies and prints on paper, but as a rule the screen is' not yet satisfactory. It is not sumciently contrasted because the silver particles have not yet all clustered in the dark portions, so that the dark portions are not altogether black and the white portions are not pure white,

silver particles being still present therein. Be

sides, the screen is coarse because, if proceeding as described, the clustering of the silver particles occurs very slowly so that the individual clusters are toolarge and not broken up as finely as rethe intermediate areas become more transparent and of reducing the width of the lines until the natural screen becomes as fine as the usual artificial screen. As ,a rule, the treatments'at the same time improve the clustering and reduce the width of the lines. It is important that the lines should be altogether black and the intermediate areas altogether transparent because, if this condition is fulfilled, the printing plates obtained.

from the screened originals can be deep-etched without important parts of the pictures being de-- stroyed.

As mentioned above, the screen may be improved by single or alternating baths with or without chemicals, heating .of:-'the1ayer before.

developing it, or by superficialdevelopment.-

In some kinds of platesthe-"formation of the natural screen is favored by a previous ageing of the developer, i. e., allowing it to stand-for along time, or heating it to the boiling point, or mixing a developer which has been thus heated, with some unheated developer. Preferably, the devel-' oper is heated to the boiling point in a dish of enamelled steel which is held at'an angle above a spirit or gas flame, the residual developer adher ing to the raised portion of the dish being evaporated to dryness and the boiling developer washing over the dry portion and absorbing the dried developer. The developer is now cooled and used at a temperatureof about22 to 26 C. This; treatment yields very clearly defined screens of" any desired fineness.

This invention further provides for the appli cation of salts and salt preparations to the fixing salt.- Such salts may be sodium chlorideor ammonium chloride. For instance, one part of ammonium. ehloridemay be mixed with four parts of sodium hyposulphite and twenty parts of water. Treatment with such salts favors and accelerates, the, subsequent formation of the screen, and prints taken from the plates or films thus treated are more harmonious and possess a more impressiveart-printing effect.

While the treatments which have been described above, relate tothe clustering of the particles to form the screen and not, or at least not principally, to the improvement of the screen itself, i. e., to the production of the maximum opacity of its lines,-'and the maximum transparency of its intermediate areas, therewill now be described treatments by which the contrast of the black lines or spots and the white intermediate areas is increased by means of reducing and intensifying agents. It will be understood that these agents are used only to produce or improve the screen, not the pictureitself; Such subsequent treatments are applied after the application of the screen-forming bath and the agents only reduce the intermediate areas and intensify only the lines of rearranged silver particles. This subsequent treatment is not exactly the same as the usual intensification or reduction of a normal photographic image in which the silverparticles do not cluster to forms black and opaque lines or spots, with white and transparent areas surrounding them, as described, but are distributed more or less uniformly and are involved as uniformly in the intensification or reduction. The subsequent treatment according to the invention renders the black portions more opaque, and the transparent ones more a transparent.

Thus, afterthe layer has been treated in the waterand then parts of a solution of five grams.

of sodium thiosulphate in 100 grams of water.

This treatment not only renders theintermediate areas more transparent but also hardens .the layer for the repeated application of screenforming baths for refining the screen.

The layer may also be treatedfor a short period with a mercury or other intensifier. I prefer the treatment with the solution of potassium ferrocyanide above described, and with a mercury.

The composition of-this bath may intensifier, it a solution of grams of r'nercuric. chloride in 100 grams of water. The

must be thoroughly washed after every bath.

.In this treatment the opposite influences of I the two agents ar'efutilized to the best advantage. The ferrocyanide, before attacking and reducing the dark portions'of. the screen, renders more transparent the white intermediate-areas, while the mercuryintensifier first intensifies those portions of the, screen which are rich in silver particles, and thereupon the less rich ones. The duration of the treatment in the baths mustbe so short that the dark portions of the screen are not yet reduced audits light portions not yet intensified, This increases the contrast between the dark' and light portions of the screen. In

. order to intensify only the dark portions of the screen without influencing the white intermediate areas, it is necessary that the intensifier should be applied only during fractions of a second, and

that the layer be washed immediately, as otherwise the intermediate areas would become less transparent. Intensification may be repeated as often as required, until the dark portions of the screen are altogether black while the intermediate areas remain altogether transparent.

If intense light is used for the reproduction of the originals, particularly with reproduction plates, it is necessary that the dark portions of the screenshould possess a higherdegree of opacity thanthat which is imparted to them by the aforesaid, treatments. This is efiected by treatment in a bath of sodium sulphide following the mercury intensification. By these means the dark portions of the screen become almost impermeable to light. v

If metal printing plates shall be obtained from the originals and etched, a uranium intensifier may be preferable-to themercury intensifier. A suitable uranium intensifier may be prepared as vfollows:

Solution I.-500 ccms. of water, 5 grams of uranium nitrate and ccms. of glacial acetic acid. a

Solution Il -500 ccms. of water, 5 grams of potassium vferrlcyanide' and 25 ccms. of glacial acetic acid', v I ..-.-;-Equal volumes of. the two solutions are mixed. Becausaof the uniform distribution of the silvenparticles in the layer of the plate, the

i uranium intensifier as a rule 'reddens all parts of a normalplate, but in a plate having a natural screen it only reddens the dark portions where the silver particles. have clustered, because the whitev portions are almost free from. silver particles. all chromates are highly sensitive metal printing plates holds not only spots which are deep black but also spots which are only grey and otherwise could not be etched on account of insumcient blackening.

Two more examples for treatments which I have found to be particularly suitable, will now be described:

I. A plate is dried in hot air at a temperature which is as high as possible without damaging the layer, say 50 C. ormore. The plate may be dried before or after the exposure. The period of exposure is reduced to about one half of the normal period. If the operator knows what kind of reproduction is required, he will consider this in the exposure. Thus the exposure should be to red and yellow, the chromate layer on the' shorter for reproduction in the manner of line etching than for half-tone reproduction. The plate is now developed with a rapid developer, such as those sold under the trade-names of Edinol, Metol, Rodinal or the like. 'If Rodinal is used, the solution should contain 5 to parts of Thiabath isstollowedby a coldswater bath having" a temperature of 8 to 10 C., the two baths bei applied alternately.

The plate may now be treated with a bath of 5 grams of potassium ferrocyanide in 100 ccms. of water, which is mixed with 10 parts of a'fixing bath containing 25 grams of sodium thiosulfate in 500 ccms. of water.

The plate may also be treated with a solution of 10 grams of mercury chloride in 500 ccms. of water and with a solution of 10 grams of potassium bromide in 500 ccms. of water. The baths may also be applied in reversed sequence.

II. The plate is not dried but is developed at room temperature in a developer containing 7.5 to 30 parts of Rodinal developer in 100 parts of water. The developing period should be as short as possible, say one to three minutes. The fixing bath contains 20 grams of sodium thiosulfate and 10 grams of ammonium chloride in 100 ccms. of water. The screen-forming bath is now applied, being a'hot-water bath of 28 to 44 C., whereupon the plate is placed for a short time in a solution of 10 grams of mercury chloride and 5 grams of sodium thiosulfate in 100 ccms. of water. The plate is now washed in cold water and, if required,

, intensified in a solution of 10 grams of mercury chloride in 500 ccms. of cool water. The plate remains in the intensifier, which is agitated, for about three minutes and is then blackened by means of highly concentrated, say a ammonia solution at a temperature not exceeding 35 C., or by'means of a solution of 5 grams of sodium thiosuli'ate in 100 ccms. of water.

The so-called reproduction plates (photomechanical or phototechnical plates) which have a very thin layer and low light-sensitivity require special treatment. In the making of electrotypes, the original negative or positive pictures are photographed on such plates. For forming the screen in such plates-,-.:,it is not. necessary to use aged developers or to heat the developer to boiling temperature, as above described, but they may be A developed immediately in a rapid developer, e. g.,

the plate is apparently black throughout. Howfor instance at 22 C. After fixation, a hot-water is applied which is contacted with. the plate from six to ten times in the manner described above.

As rapid treatment is often important for such plates, the fixing bath is preferably prepared with a rapid fixing solution containing for instance 20 to 40 grams of sodium thiosulfate and 5 grams of ammonium chloride in 100 grams of water, and the fixing bath is applied in warm condition has been found that the temperature of the bath should be between and 31 C. and on no account above 32 C. The water in the hot bath is contacted with the plate two or three times as described, but only before the screen has formed and until the layer has become mat like velvet.

The duration of the application ofthe hot-water bath is 10 to 20 seconds and it is followed by a cold-water bath. which is applied until the layer has cooled down to the temperature. of the bath.

Its duration may for instance be five seconds. The treatment with the alternating baths is continued until the screen is black throughout the intermediate areas being altogether transparent,

care being taken to prevent detaching of the layer. A longer application of the alternating baths renders the screen coarser. If there are still too many grey shades in the plate for etching, the plate for one or two seconds is placed in a strong solution of. potassium ferrocyanide, containing for instance 10 to 15 grams of ferro-cyanide and 4 grams of thiosulfate per 100 ccms. of water. The reduced plate is placed in a cold-water bath, and this treatment is repated as often as required.

Old and dry plates may also be subjected to the treatment for forming a screen therein. If

a plate is alreadyprovided with a natural screen,

this screen becomes finer by the repeated breaking-up of this structure. Old plates, developed plates, fixed and dry plates are placed in water of about 25 C., preferably after having been previously heated to about C., as described. In autotypes produced in the old way with separate screens the raised portions of the etched printing plates are protected fromthe attack of the etching liquid by a coating, in order to obtain more plastic reproductions. The natural screening according to this invention permits a more simple and more efficient operation by applying to the screened layer itself black color with a colored pencil. In this manner the plate can be retouched by means of black lines and areas, while in the autotypes produced with separate screensv the covering could only be altered in spots.

By the engraving of certain lines of the image on the layer of a plate having a natural screen, down to the support (glass) of the layer, (this being old in theart) the effect becomes more harmonious than in layers formed with aseparate screen, and the reproduction gives the impression of an engraving; The treatment is facilitated by the plate being colored red or yellow after the screen has been formed, as this presents ity of the etching which can be performed, and

it is possible to perform the etching in a singleoperation which was heretofore practicable only at the expense of the contrasts. Etching may be extended much more-deeply than was heretofore possible even with repeated etching, for instance with strong acid such as is used for line etching. A suitable acid may contain 15 ccms. of concentrated nitric acid in 100 ccms.'o f water. The contrasts may be so strong that upon etching the highest lights or the lighter shades disappear altogether. The highest lights are the finest metal 'cones which remain behind. If they breakdown, this only increases the plastic effect of the reproduction, as it occurs only in the lightest portions of the picture. In this manner, the original is reproduced with all its shades, or the reproduction obtained is modified, until its effect is substantially equal to that of a line etching made by hand. This variety of reproductionsmay be made selectively from one original.

If, for instance, it is desired that the reproduction should give the effect of a line etching, the exposure should be shorter than normal so that the latent silver image becomes rich in contrasts, with the half tones comparatively undeveloped and the contours of the image standing out distinctly. For the same reason the developing period should be shortened. The screen in the negative, however, must not show in these portions of the copy or print which are either absolutely black or pure white but only in the intermediate shadings or half tones. The lightest portions of the copy or print which correspond to the absolutely black portions of the negative,

shades, disappear altogether, so that only the;

contours of the image remain as the printing .surface. This may be effected, for instance, by-

If, on the other hand, a half-tone reproduction is desired, the operator should perform the treatment so as to obtain a less strong contrast, 1. e., the sensitive layer should be overexposed and developed for a longer period, the formation of the screen should be more effective, and the etching less intense.

The reproductions or prints from etched metal plates which have been obtained from an original with a natural screen, can thus be made more artistic and more similar to engravings, but above all with more intense contrasts. Not only normal printing paper of various kinds can be printed with such plates, but also other materials.

such as rough paper, cardboard, linen, cloth, silk and other textile materials, wood, cellulose,,cel-

luloid, artificial resins and the like, glass, porcelain, fayence, stoneware and other ceramic materials, something which was heretofore possible only with expensive manual work, such as drawing, engraving, etc. i

A particular improvement achieved by this invention is the possibility of directly printing photographic layers. This has already been attempta hardener.

ed but proved an absolute failure. I have found, however, that by operating with a natural screen of the kind described, and by using the photographic layers themselves as printing plates, very good prints are obtained. The same applies to galvanoplastic products which can be made directly from such photographic layers.

The new method which brings forth the natural screen is superior tothe old methods not only in the printing with electrotypes and in book printing, but also in plain, offset, copper-plate and phototype printing. In particular, in the four last-mentioned printing processes all that is required is to make a lantern-slide copy from a negative provided with the natural screen without the formation of the screen being repeated in the lantem'-slide copy. The screened originals may be plates or films, and they may be photographed on plates or films, as desired.

It has already been mentioned that my method is advantageous if applied to plain printing. It

-must also be stated that I can apply it to lithog-.

raphy and related arts. From the layer with the natural screen, I obtain a phototype layer of gelatine on stone, zinc, copper, or the like, and can make double tone reproductions from this gelatine layer. a

The new method is also particularly important for the printing of bank notes and photostat copies of documents or the like. As the natural screen never forms twice in exactly the same manner, the new method provides an infallible means for ascertaining whether a bank note is genuine, i. e., whether itwas made from the original and from the type of a given series. Not only the arrangement and clustering of the silver particles will never repeat itself, but it is also very difficult to exactly-imitate the etching as it is found in a given plate.

The new method may be applied to letter-press as well as to copper-plate printing. In letterpress printing more copies are obtained from a given type than in copper-plate printing which was heretofore exclusively applied to the printing of bank-notes, because letter-press. printing requires much higher pressure than copper-plate printing, so that the life of the type is shortened.

The formation of the screen and/or the etching may be so performed that the characteristic features of the screen are visible to the naked eye on the reproduction.

This invention further relates to the image. bearer itself, or to its silver-halide layer; the silver-halide layer must be selected in conformity with the desired character of the natural screen. As has been stated, the layer should be harder for reproduction by printing, and softer for photographs. On the one hand, it must readily be transformed into the jelly-like condition required for facilitating the movement and the'clustering of the silver particles, while on the other hand it must'not meltcompletely. It has already been mentioned above that the silver particles should float in the layer.

To this end the silver-halide layer is made of soft gelatine or mixed with a small percentage of Such hardeners are dispersed substances which solidify the gelatine, for instance starch, chalk and the like. Preferably, the hardener should be made of a material which is as transparent as possible, or, in the case of a material which is not light-permeable, such as chalk, it should be dispersed so finely as not to interfere with the transparency of the layer; A suitable hardener may conteain equal parts of gelatine and starch, for instance rice starch. The object of the hardener is to enable the layer to stand a hot-water bath of the temperatures indicated above without being dissolved, while on the other hand the layer must not be rendered so consistent by the action of the hardener that it interferes to any appreciable extent with the free movement of the particles.

Soft gelatine is preferable not only because it facilitates the free movement of the silver particles, as described, but also because-it will assume the jelly-like condition permitting the formation of the screen at low temperature. Therefore, with, a layer of soft gelatine, the screen-forming baths may be comparatively cool and the proper temperature of the bath is more easily ascertained.

It has been said above that the layer may be dried by being heated to about 50 C. before being developed, in order to partly or completely expel its water, and that plates may be marketed for the Tropicsin dried condition. This feature is of general importance.

Superficial development has already been referred to, and its advantages havebeen explained. Another advantage of a superficial development is that the layer with the screen is supported on a resilient stratum, i. e., the undeveloped portion of the layer.

Such strata or intermediate layers may also be inserted between the layer carrying the screen and its support, i. e., the glass backing of a plate, or the Celluloid backing of a film.

The plate or film shown in Fig. 3 has two intermediate layers, 3 being the glass or Celluloid backing, as the case may be, 4 being the layer in which the screen is formed, and 5 and 6 being two intermediate layers which are interposed between the screen layer and the backing 3.

Any number of intermediate layers or strata may obviously be provided. The principal object of the intermediate layer or layers is to provide a resilient support for the developed silver-halide layer 4, since the intermediate layer remains resilient notwithstanding the exposure and development of the silver-halide layer. The intermediate layer may howcver also be utilized for influencing the treatment of the silver-halide layer. Thus, some developer or some fixing salt may be admixed to the intermediate layer, or, if more than one-intermediate layeris provided, one of the agents may be admixed to one, and the other agent to the other intermediate layer. In this manner the developing and/or fixing of the silverhalide layer is greatly accelerated. Substances such as ammonia, ether or the like, or a m ixture thereof, as described above, may also be admixed to the intermediate layer or layers.

Instead of chemically active substances, there may be admixed to the intermediate layer or layers hardening agents as described, for instance, starch. An intermediate layer in which the gelatine is bound by a dispersed hardener, permits reducing the silver-halide layer to a. softer condition than would be practicable without the intermediate layer, because the silver-halide layer, if softened to a condition in which it would come off a glass or celluloidbacking, will still stick to the intermediate layer which, being hardened, retains the silver-halide layer.

If more than one intermediate layer is provided, as shown in Fig. 3, the outer intermediate layer 5 may contain an admixture of a developer, while the inner intermediate layer 6 may contain an admixture of fixing salt. The layers may be hardened to different degrees of hardness, the

outer layer with the developer admixed thereto,

the inner layer i is-softened in its turn and'libcrates the fixing salt. In other words, the hardness of the intermediate layers should increase in the direction from the silver-halide layer -4- toward the support or'backing 3.

Various changes may of course be made in the details disclosed in the foregoing description without a departure from the essence of the invention. I claim: v

1. The method of producing a printing plate, comprising exposing and developing a light-sensitiveizsilyer-hallde, layer, treating. said layer so as to cause the silver particles therein to become rearranged to form a screen, exposing a sensitized metal plate throughsaid layer, and etching said plate. l

2. The method of producing a printing. plate, comprising exposing and developing a light-sensitive silver-halide layer, treating said layer so as to cause the silver particles. therein to become rearranged to form a screen, exposing the lightsensitive chromate'layer of a metal plate through said silver-halide layer, treating said chromate layer so that certain portions thereof expose the metal of the plate. and etching said metal plate.

"3. The method of producingxa printing plate,

, comprising treating a light-sensitive silver -halidelayer-so as to produce therein a photographic image and cause the silver particles in the layer to become rearranged, resulting in the formation of a screen in said layer, making a printing surface from said layer, and treating said surface for obtaining a printed reproduction of any desired character. I

4. The method of producing a printing plate,

comprising treating a light-sensitive silver-halide 7 layer so as-to produce therein a photographic image and cause the silver particles in the layer to become rearranged, resulting in the formation of a screen in said layer, making a printing plate from said layer, and etching said plate as required by the character of the prints to be made therefrom.

5. The method of producing a printing plate, comprising treating a light-sensitive silver-halide layer so as to produce. therein a photographic image and cause the -silver particles in the layer to become rearranged, resulting in the formation of a screen in said layer, making a printing surface from said layer, and treating said surface for obtaining a. printed reproduction resembling a line etching.

6. The method of producing a printing plate, comprising treating a light-sensitive silverhalide layer so as to produce therein a photographic image and cause the silver particles in the layer to become-rearranged, resulting in the formation of a screen in said layer, making a printing surface from said layer, and treating said surface for obtaining a printed reproduction resembling a half-tone engraving;

EMIL EDUARD ECKARD'I.

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