US2374910A

US2374910A - Indirect photomechanical reproduction

Info

Publication number: US2374910A
Application number: US424582A
Authority: US
Inventors: Francisco G Yanes
Original assignee: PHOTOPLASTIC CORP
Current assignee: PHOTOPLASTIC Corp
Priority date: 1941-12-27
Filing date: 1941-12-27
Publication date: 1945-05-01
Anticipated expiration: 1962-05-01

Description

Patented- -May 1, 1945 INDInEcTrHoToMEcHANIcAL REPRODUCTION Francisco G. Yanes, NewYork, N. Y., assignor to Rhotoplastic Corporation, 4New ;York, N. Y., a corporation of New York l Application December 27, 1941, Serial No. @$4,582 I .z2 Claims. (ci. roi-401s) This invention relates to indirect photomechanical reproduction and includes printing sur,- faces that can be utilized in typosraphy. The Isystem* is indirect because the printablevalues are-firstly obtained in reversed relief by developing a special lelement -into amould from which a final printing surface may be cast. 'Ihe invention comprises lmeans, ways and products.-

In most photoreliei' processes it is sufficient to reverse the steps to produce a mould instead o! a printing surface; this is done by'using a posi'- tive instead ofa negative as a master record, or by etching away values that are usually hardened and -preserved. with the occasional variation of reversing also the direction of the exposure in order-to utilize as bottom in themouldthe even surface of the supDOrt carrying the sensitive coating. Examples of such indirect'way of producing printing surfaces may be found in the literature of the early art; among other suggestions Namias proposed to exposethe plate through a trans parent support, and Waterhouse to produce an image on a carbon tissueand transfer and develop it on a metallic plate; in those and similar' processes, however, the-production of half-tone plates makes necessary to firstly transform the photographic values into photomechanical ones in the known process-record, where the tones appear divided in sections of different areas; and'further, when. the steps are reversed, and instead of a. printing surface a mould 4is obtained, the casting ofl the final plate constitutes an additional,

step,'for such methods, rather than indirect reversedly practiced direct ones.

The production of half-tone printing blocks without a process record, by exposing under an ordinary negative a sensitive coating having de pressions or recesses decreasing in cross-sectional area, was suggested in a method of direct photomechanical reproduction described in Patent No. 2,234,997, issued March 18. 1941. The sensitive element utilizediin that direct method includes two forms; in one of them the depressions are filled with a transparent support through which the element is exposed, and in the other form the depressions are not filled, for the final support is provided after the. exposure, the sensitive coating being provisionally carried by a porous temporary support. Of these forms the first cannot be reversedly processed to produce a mould, for

are

fmayuse, instead of a porous an impermeable rigid support and, instead of a`soluble coating, a thickness of hardened sliver emulsion. When in such modified element, on the side having the depressions, a photographic image is produced, developed, and etched in known manner, a mould is obtained; andwhen a cast is taken therefromv no additional step is performed, for what would have been a support for the exposed depressions in the direct system, now fills the etched ,cavities and becomes shaped, instead of furnishing as before a high-light foundation with additional values rof hardened gelatine. The new product is better and preferable, for lthe final block, as made of a single substance, is more resistant. Such indirect methodof reproduction is not a reversedly practiced -form of my direct system, for the means utilized are different; after the modifications in I troduced in the support and coating of the eleminute depressions decreasing in cross-sectional neither'the use of a positive instead of a nega- Y tive, nor the etching of the values that are usually preserved,would render such result-due to the already existing high-light projections. In the second form, however, the order in which the W steps of the processing are performed otl'ers at Y area and sharply ending on the other side.

The described variation was yet the point of Y departure in the development of the present in-` vention. Photoreliefs of gelatine 4and other equivaient substances are the subject of certain precautions in typographie printing, for although most objections formerly made to such type of elements are today overcome by suitable treatments, there isfalways the possibility of careless handling for materials extremely sensitive to dampness and which may have to undergo the test of steam and pressure, as when mats are ldried on the form in the stereotyping process.

When such totally or partially colloidal plates are used as moulds, there are also limitations in regard to the possible system of casting, especially in electrolytic solutions, For these reasons, after having eliminated the colloidal matter from the final plate, I endeavored to also produce an all purpose mould, susceptible of serving in any systcm ,of casting and duplicates. i y e I have found that the demarcation of the etchableV zones by the effect of light, was not necessarily indispensable in producing photomechanlcal values in asolubleelement shaped as the one for any kind and number of is treated by a solvent, so that some oi' the cavities be preserved, some others dissolved for a given time, and the remainder for a longer time, it will be seen that the dissolved cavities are enlarged figures geometrically similar to the undlssolved) ones, and that'the respective sections at the original ending plane substantially correspond to the printing area of high-light, half-tone and shadow dots. Now, if those small depressions or cavities are suitably disposed in a copper plate as to provide a high-light casting pattern, and the plate is etched, with a solution of ferric chloride, proportionally to the values of a photographic image, it also will be seen that the copper foundation or ground has been developed into an excellent mouldfor a half-tone block reproducing all the tones of the image, and showing values in surface formed by small areas or dots of dierent sizes similar to those produced in the photoengraving process.

As to the manner of proportioning the etching to the values of an ordinary photographic record, there are several known reactions which may be utilized, including both the direct and catalytic action of a photographic image, to make active orto free certain reagents, and even to determine the electrical discharge of matter. I prefer, however, to use a gelatine resist in which the.

permeability is proportional to the values in -depth and fully controllable, for among the varied resources of the art itis one of the practical ways of performing the selective etching of the high-light casting ground utilized in the invention.' I found that a gelatine layer carrying an image, as a carbon tissue print, for instance, adhered under water to such uneven surface as that of a. plate having depressions or recesses `forming a high-light casting ground, will, during the processY of drying, absorb the water retained by the small cavities and become substantially attached by suction to said cavities, just as if the surface were as smooth and even as an unetched plate or cylinder. it further behaved through the developing and etching operations as an ordinary resist in intaglio processes.

The development of photographic values into photomechanical ones by the eifect of etching is not new in general, for such technique is utilized in photogravure. However, in the known process the etching proceeds downwards from an even surface, and whatever be the area initially dissolved, it remains nearly the same for a given cavity atv different depths, and also for other cavities initially having the same area; because in photogravure the photographic values in depth are transformed into photomchanical values also in depth, these values consisting in cavities or pockets more or"1ess profound in which dimerent thicknesses of uid ink are deposited for the printing. In the 'present invention the etching does not proceed from an even surface but from within depressions or recesses sharply ending at the same plane; as a resultof the etching operation those depressions are widened and, when the time of etching is not the same for all the cavities, a sectional plane at or near the original 'depth of therecesses willshow sections of difierent areas corresponding to the extent in which the widening had been developed in each cavity. 'I 'he photographic values in depth are thus automatically transformed while the etching goes on into photomech cai values in surface. as those produced by the 'otoengraving process.

The indirect system thus permits producing And I also found that lprinting surface by selectively discharging matter from an element of special structure, which can be either sensitive to light or totally insensitive, a photographic image in the first case being produced in the element for the demarcation of the etchable zones,` while in the second case the image is obtained elsewhere and according to the described example, transferred on the element to control the etching time. In this second, preferred form, a printing surface can be produced not only without a process or screened master record, but even without the previous optical transformation of the photographic values into photoengraving ones that takes place when utilizing a sensitive form of the element.

.The etching of the totally insensitive to light on a non-sensitive structure, it may be observed' that the effect of light in the first, and that of the etching in the second,'are so similar within a moulding cavity decreasing in cross-sectional area, that the two phenomena seem to develop the same results. There are, however, certain advantages in favor of the etching step.I Discounting a' slight irradiation within a sensitive coating. light only proceeds in a straight way, thus actng in depth; while etching acts both in depth and side-ways; and for that reason the sort of lateral edect of light in the sensitive element has to be created by prolonged exposure of' a special structure presenting different ,decreasing resistances at` different depths. In the case of etching the lateral action already exists and it seems rather augmented within the same structure. This explains why when light-values representing a photographic image fall within the cavities of my sensitive structure it .is indispens able that an insensitive support should stop the light effect and develop the values in surface, for both the structure and the sectional plane at the bottom of the cavities are necessary for the optical transformation of the photographic' values. while in the etching proper, of an inaensitive structure, only one or the other of the two features is essential; for if the cavities do not decrease in cross-sectional area but Just have a sharp-end, it would be sufficient that the etching be limited by an unetchable substance at the bottom of 'the ground for selectively enlarging e of those cavities by a prolonged treatment, and this on account of the existing lateral effect of etching; on the other hand, if the cavities are shaped as to decrease in cross-sectional area without any arrangement to stop the etching. the already existing lateral effect of etching is so increased by the structure and becomes so predominant that the values at the bottom of the mould are developed beforeany objectionable difference in depth is produced.v The ending planes, of such differently etched values, are so near in that case that plates cast therefrom are perfectly printable.. f

When utilizing the etching step, it is, of course, desirable for a neat dot.I that all the values be on 9, the same printing plane; and, to save etching element.

Fig. z'illustrates in four stages examples of, means, ways, and products of the present intime, that the cavities should also decrease' in cross-sectional area. The printing values may be obtained on the same plane by mechanically eliminating in the cast the excessof height of halftone and shadows, but it is preferable to do so in the mould, by forming the element of two substances, a soluble thickness carrying the depressions or recesses. and an insoluble second thickness supporting it at the ending plane of the cavities. In this manner the etching in depth are used such as cones, Pyramids, bases, vertices, tangent or ending planes, similar figures, and the like. As such words usually convey an exact and mathematical meaning, it must be understoodv that, within the limits of operativeness,

i they are not purported to so confine and restrict is limited and the values are developed on the circumstance most desirable in making partA plates. As to the resulting mould, it will be suitable for wet, dry, cold, hot casting, including embossing, stamping, vulcanizing, moulding of a1- loys, and el yctro-deposition, all without any special precautions.

The means and ways cf the present invention lend themselves to many industrial applications', and in the art of printing to several kinds of work, but for the purpose of demonstration it the invention in practical manufacture. The same remark must be made in regard to expressions describing requirements of matter, only purported to materialize functions, or rather means to perform certain results, and which must not be construed as absolute but only as sufficient and operative for the purposes of the invention. Substances qualified as soluble or insoluble are only thus considered iii-.regard to a given solvent, andeven soin the' extent necessary forY the intended result, the insolubility'being possibly partial, superiicial, or artificially completed by an added protection, as long as such property is only utilized to stop the progress 'of thexetching or discharge of matter from the body of the element utilized inthe process.

For the purpose of comparison with the present invention I shall firstly describe how I may indirectly produce a printing, surface by utilizing the element diagrammatically shown in' the rst stage of Fig. 1. This element is sensitive to light and, with some variations, has the same struc-Y ture and sensitivity of one of the photographic materials described and claimed in Patent No.

; 2,234,997. `As presented in Fig. l, the'element is will be sufncient to describe, in the following disclosure, the production of half-#tone printing surfaces for which it is advantageously adaptable. Examples will also be found showing the possible varied and equivalent forms that such means and ways may present for dierent graphic purposes. The invention is graphically described in the4 following drawing which illustrates sectional views, the ones showing the heavier shading corresponding to planes passing by'the Jbottom of the small cavities present in the grounds where the moulds are developed. These views have been chosen as the best to demonstrate the invention and represent depressions in which the different reliefs are under the. surface, while the views showing a lighter shading represent the casts or final plates which are reversed structures' formed by projections: V A

Fig. 1 diagrammatically` shows, in four stages, and for comparison, -examples of means, ways,

-and products, in the indirect production of a utilizing a light sensitive printing surface by vention in the indirect production of a printing surface from an element insensitive to light.

Fig. 3 presents a variation in the means shown in Fig. 2, for producing all the values on the same printing plane. y

Fig. 4 is another variation of Fig. 2, both in means and ways, to produce tone and shadow values on the same raised plane, and lowered righ-lights i'or pure white effect. l

Fig. 5 is an example showing possible variations of ways in the practice of the invention.

Before entering into a detailed disclosure of the means, waysand products of the invention it seems convenient to explain that both in their description and defining claims a geometrical language has been adopted to facilitate the understanding ofstructural requirements. yTerms formed by a waterproof, rigid support l2, carrying a coating of hardened silver emulsion I, which has a num'berof small depressions or recesses l, decreasing in cross-sectional area and sharply ending at the plane of contact Vbetween emulsion and support. The variations introduced in the new element consist in that the support is not porous and the emulsion is not soluble as in the element purported for direct reproduction, for neither one are intended to be eliminated by washout, but the first to furnish the bottom of a mould and the second to maintain the shape of the depressions 1, through the photographic operations. The second stage in Fig. 1, shows the sensitive element after an image 3, has been produced and developed in it. The optical transfor- 'mation of the values is there performed on the 4 fourth stage of Fig. 1, the final cast Il, of the indirectly produced casting surface is illustrated, the product being substantially identical in outline to the final plate Vdescribed and claimed in the patent above referred to, except that the printing vblock is now formed b ya continuous body in which not only the` high-'light dot I, but all the printing values together with the' supporting thickness are made of a single substance. Such new product'is an improved printingsurface which maybe cast in varied substances and by different moulding ,systems consistent with the colloidal nature of the 'casting values l, suitably hardened and protected.A I prefer, however, to produce-the same article by the indirect methociv of the present invention Afor it offers a wider choice both of substances and casting technique as I shall now demonstrate.

Fig. 2, shows. in four stages, means, ways and products of the present invention, which is not -a variation of any direct system, but a genuinely indirect method purported to produce, and which can only produce, a moulding device from which the printing surface may be cast. The element -light tint formed by smallsdots as those that represent the conventional whites in half-tone plates. Such element E, is purported to be selectively etched in order to develop some of the high-light casting cavities into larger cavities for moulding half-tone and shadow printing dots. In regard to structure it is desirable that the angle of the cavities be as wide as possible, consistent/with the known-.average printing depth of printable half-tone plates, a question fully discussed in Patent No. 2,234,997, issued March 18, 1941. It seems obvious that as the purpose of that requirement oi widthis to save etching time and to suiiiciently develop the side etching of the cavities before they should attain any objectional depth, it is not indispensable that all the extent of the cavity vshould have a decreasing cross-sectional area provided the requirement is present near the bottom Where they sharply end. The essential question in the structure of the cavities is that they constitute a moulding device for very light printing values which can be developed into darker values by etching or dissolving away matter fromv the inner walls of said cavities, and .thus the developable ground of the rather unfinished moulding device must be so shaped or modified as to speed up the side etch'- ing in preference to theletching in depth. The form of cavity lillustrated in the first stage or Fig. 2, has been adopted as most suitable for the purpose. As to matter, copper has been preferred for the example, to form the soluble thickness 6, because not only it is easily dissolved by ferric chloride, but will stand casting in any kind of moulding oi known printing surfaces, at temperatures which never reach or approach the vmelting point of the metal. For casting typealloy, brass' would also do, as it is etchable in the same way; and so would aluminum, which can be dissolved in acidifled solutions of the chloride,

for castings conveniently under a terperature of plate may be produced by engraving crossed grooves on a thickness of brass, as the shaping plate described and claimed in the above cited patent, taking an imprelon of this in phenolic cured resin, and then duplicating the. last. Orr

the master plate may be directly cut in steel to furnish a tempered die'with which copper may be embossed or stamped. Instead of the pyramidal shape oi' the cavities. a conical form may also be secured by drilling the minute cavities in a small area of brass, and then multiplying the elements by casting, asl type is made. The developable ground can also be produced by etching, especially for iine patterns, in well knownman'ner. I' prefer the crossed groove type of ground for it has less matter to be etched and besides shortening theprocessing time it furnishes very satisfactory values. For other substances a similar or other suitable way may be utilized which seems prolix to discuss. The general outline of the their original shape a ground may also affect the manner of producing, it, as when a convex o'r concave cylindrical ground be desired, for which suggestions exist in the art that can be freely adapted to the purpose. Rel garding the form of the dots, there is not a spe cial limitation, for many graphic elements such as small squares, commas, straight or undulated lines, both regularly or irregularly distributed, would be satisfactory provided they furnish in high-light pattern susceptible of being developed into similar larger values as those' presented in the example. A suitable iry regular ground may also be formed by dusting and etching; or from a swollen photorelief; or

by evenly distributing cracked particles on a sticky coating in the manner of sand-paper or emery-cloth, until the repeated test furnishes a neat print of a high-light tint" which is then duplicated and used as a shapingselement. The

40 number of cavities for a given area is only restricted in the example by the possibilities of the printing system adopted, and for the case of typography it may be practically fixed between a minimum of thirty and a maximum of two hun- "I dred and fifty depressions per lineal inch, other 660 F. zinc is another metal that couid be uulized, for it is equally etchable, at least for the stamping of plastics which usually can be formed at temperatures under 300 F... thus giving a margin of more than 100 degrees before the melting4 of the metal. In addition to this, the choice is wlde among natural and synthetic, organic andinorganic, simple or compound matter .which can be, suitably dissolved and if necessary cured or hardened by after-treatments. Obviously, substances that would do for cold moulding may not be satisfactory for stamping or embossing.

under heavy pressure, orwould :not stand certain temperatures or the immersion` in solutions for electrolytic deposition; but while the system of casting in view will direct a convenient choice, copper seems the best for an all purpose developable moulding ground. The selection of a sultable substance 'for the etchable ground is not limited to compact and continuous thicknesses, for even the metals can be laminated and formed from powder and a suitable binder, all depending on the moulding to be performed.` The selection of matter will also aiect theproduction of the ground. When using copper, a master forming" graphic purposes permitting to use coarser or finer patterns. In the second stage of Fig. 2, the insensitive element appears protected by a negative resist of gelatine 8, which may be separately printed from a photographic positive transparency and transferred and developed4 on the ground. After the resist is conveniently dry, the etching of the copper ground is made with ferrie chloride in known manner which will be later discussed in detail. In the third stage of Fig. 2, the developable ground is illustrated after the etching has taken place, the casting sections lla, corresponding to half-tone and shadows, being exaggeratedly shown as much deeper than the preserved high-light cavity; such difference is also shown in the cast -I la, of the fourth stage, Where the khalf-tone and shadow dots 9, are much higher than the high-light dot 5a. In practice,

when the structure ofthe first stage is etched, the

difference in height may not beso pronouncedv for the resulting surface is printable and also susceptible of improvement by sanding off thev surplus of matter in known way.

Another 'form of the invention is shown in the w four stages of Fig. 3. In the iirst,.the general outspending to the depth of the cavities 1a, which' line in the structure of the element is the same as before, but two'sub'stances are utilized in the body. The upper section 6, is made of copper or equivalent, in a thickness substantially correment.

end at the surface o1' a second thicknessof matter` Ill, adhered to the first thickness and made of' nickel or substance equivalently insoluble in ferric chloride or whichever solvent be adopted for the upper thickness 6.- In the second stage of Fig. 3, the element appears protected by a negaeasilyeliminated if desired by. prolonging the etching. In the fourth stage the cast I Ib shows the preserved vhighlight dotb and `the shadow values 9a whichare now all on the same plane.

This final plate h'as levelled values as-the usual half-tone printingplate and the dots are sharp and -even vsurfacedriueA to the insoluble section IIJ which stops the etching in depth. I'his type of element affords to utilize a variety of lforms in the cavities, for as long as the'insoluble thickness stops the etching it would-Ibe a question of time to develop the high-light values into darker ones. -I may produce the stratified material by stamping a copper foil of suita'ble thickness and then deposit the nickel by thecurrent; but of course any insoluble substance, as a cured phenolic plate, may serve as support. The copper may also be deposited electrolytically. Orthe copper may be welded to or deposited o n a hard metal vand stamped thereon. In fact the pair of substances adopted may be'easily joined by aV number of methods freely-practiced in different arts.

In Fig'. 4, another frorm'is illustrated in which the element of the first-'stage is similar. to the one in the'preceding figure.- and hasthe soluble section 6, of 'copper or equivalent, andthe unetchable section I0, of 'nickel -or other equivalently insoluble substance.

.In this element, however, the two thicknesses 'are not put in' contact,- but separated by single or plural thicknesses of matter o'f varied solubility, of which the one yillustrated as example in I2 is made of aluminum or equivaient. As the selective protection o'f the element has been villustrated in Figs. 2- and 3, the, second stage of Fig. 4 shows the already etched ele- It may be noticed that-thecavities 'Ib of the first/ stage are not sharp but represent larger dots than high-lights which by the etchine.r of the ser-ond stage are widened into stronger values. with the exception of the preserved cavity that would correspond in the original to a highlight section. After the etchingl shown at the second stage the intermediary thickness I2 forms l.tive resist oi gelatine 8a, which, for a fine pat terned ground,may correspondto a line subbeen illustrated as having depressions which do not sharply end, for as long as the high-lights will not etch an-d will print no dots, the sharpness of these casting values is immaterial. The resulting printing surface II'c, in Fig. 4, corresponds then to a half-tone with pure whites as` those utilized in photo-lithography. As to the thickness I2 it may-be built as to pro-vide in several strata different degrees ofdepth and to suit the desired difference of height in the values. In the same Fig. 4, the first and second stage show, as example, other means I3 for controlling the etchable zones which may equivalently consist of surface protection or unetchable matter suitalbly distributed and purported to delay the etching of given sections in order to attain special results and effects that is noi'l considered necessary to illustrate. In other words, whether bare or protected, the surface of the ground will hold the resist or other control'for the selective etching, but it may be advisable in certain cases that the sections at the outer surface of -the ground in immediate contact with the controlling elementhe notvdirectly etchable and should disappear only by undercutting and this in order to 4 minimize the-danger of separation of the resist during theetching. In the example, the minute .depressions of pyramidal shape sharply end in dots at the bottom, but on the outer surface are separated by thin walls similar to gravure pockets, and the means I3, I3, may be provided for protecting the outer sections of the walls, or may be suitably distributed in many other forms to control the etching.

In Fig. 5 three stages are presented showing a manner of producing a casting mould in other ways different from the ones already described. In the figure the bare element and the final cast are omitted' as being identical to the first and fourth stages of,Fig. 3. Although other examples could be presented, the way adopted in of the invention. In .the first stage of this iigure the cavities in the copper ground appear protected by three varnishes of which I B and I -I'I are soluble in two different solvents, and I8 in water. These lvarnish'es are colored in-white,

gray and black respectively, so that an artist can paint a subject on the plate. Rather than using a greater number of varnishes and selective solvents, or protections of varied permeability; it is the bottom of the moulding values 4c, for a nonacidified solution of ferrie chloride does not substantially etch aluminum, which may also be proout the gelatine resist, has been submitted to 'a ,60. tected In the third stage the element. now withsecond etching with hydrochloric acid which does .preferable to use the three fundamental values and lgive selective etching to the half-tones by successive re-etching operations. When the protected plate of the first stage in Fig. 5 is put into the solution of ferrie chloride the protection I8 dissolves in the water, and the shadow sec-4 tions are attacked by the solution as shown in the second stage. After the shadows are suitably etched the plate is withdrawn from the bath and the half-tone protection washed away in-its solvent. When etched again the shadow casting values I8 will have their full development as seen in the third stage, while the half-tone cavities 20 will be formed, and the high-light casting values IB` will remain preserved. As the highlight and extreme shadow values, respectively protected 'end unprotected are now unchangeable. any gradation desired at selective sections of the half-tones can be produced by re-etching. the insoluble thickness I 0 showing by contrast with the color of the copper the progress of the operation. The resulting cast will print an artistic half-tone image. If desired the same weibod can be applied to the element of Figd to produce an image with pure whites, the second etching of the section I2 in that figure being made after the selective discharge and the desired reetching of the values have been performed. Such way of performing the selective discharge of matter at diilerent'areas of the developable moulding ground is only presented as example of posasumo Baume concentration, although, 'even then, ,it

. should be remembered that the high-lights must be absolutely preserved from any etching. When the developable ground shown in Fig. v3 is utilized, the unetchable bottom behind the copper surface shows the image in all detail, and a se- 'y lective etching may be carried accordingly, for the printing-depth is limited and'only the values sible variations for the same results may be attained in other manners as formerly stated.

In the examplechosen to demonstrate the invention, the selective protection is a photographic in surface have to be considered, which is one oi the greatest advantages of the process.

After the etching is finished the now developed ground is cleaned in potash, and the oxide regelatine resist shown in the second stage of both certain points in which the general technique may be modied and advantages and simplifimoved in weak hydrochloric acid. The mould is then ready for use. And this first product of the invention will be suitable for all casting purposes.

The second product of the invention is the cast, which may be formed in any desired way and with any moulding material. In the line of thermoplastics, any number of cuts may be produced cations which can be adopted. I use as master reqird for` the reproduction a positive transparency reversed from right to left. To sensitize the regular black tissue on the market I utilize a bath with a bichromate concentration of 3 percent, or the known spirit sensitizer. I

usually expose to photoiiood lamps and, as there is not any screento be printed, no precautions about the lightsource need be taken. -Any photographic printing frame is satisfactory. I may use the developable moulding element of Fig. 2, which is a high-light moulding ground 4of copper. This is freed of grease by the known treatment with potash followed by dilute hydrochloric acid. The element is then well rinsed and left under water for the transferring. 'Unless for a number of pictures, requiring transferring time, waterspirit may be dispensed-with and plain water transferring adopted. The tissue is placed in the water, freed of air-bells and watched until the curling begins to disappear: then it is turned face down and at the moment when it looks flat. it is brought into contact with the copper ground and lightly squeegeed on the last, preferably under water. Then the two are taken out, sponged and put to dry; At this point it is interesting to note that no pressure should be exercised to secure the adherence of the resist which at the initial contact is only held by the outer surface of the walls oi' the cavities then filled with water. This water ienot to be disposed of by squeegeeing or other forms of pressure which -might harm the image; on the contrary, it should be left alone, forit is gradually absorbed by the upper layers of gelatine as vthe drying takes place on the surface, and a sort of vacuum suction develops inside of each cavity which seems to bring the tissue into contact with the inner walls oi' the depressions. The development is performed as usually and the drying ofthe resist adjusted to working room conditions. When the outer surface of the ground is protected as in I3, Fig. 4, the etching does not 'require special precautions for the protection is equivalent to the screen printed on the ordinary resist of photogravure. But when, as in' the example now being described, the ground isbare, it must be considered that the walls of the cavities are also etched under some sections of theV resist and While the adherence persists it must be carefully handled. Oi' course, such is not the situation in a surfacely `protected ground, which would allow to carryF the :mmm m mm1 bains ad down-t0 the as 15 of very light Weight, sultablefor mail service of a chain of syndicated newspapers, for instance.

With melted alloys, printing blocks may be prol duced in a composition machine, by an attachment lthat I have devised, in the same manner as lines of text are cast. Cuts may belobtained in vulcanized rubber, in cured phenolic resins, as well as-in Acold moulding of setting materials. The new block will be most suitable for stereotyping, due to the open shape of the dotswithout the dangers of dampness and heat when drying the mats on the form. It will be in general,

an all purpose product in photomechanical reproduction.

summarizing:l the means, ways and products oi' the invention, as disclosed in the example, will permit to indirectly produce a half-tone printing block of the best quality, not only without utilizing' a process-record, but even withoutthe optical transformation of the values. y

The invention also permits to'produce a halftone of the lithographic type in which the whites are pure,` as shown in Fig. 4, by -an additional etching performed in known manner. In 'this case only half-tones and shadows are printable It further allows to produce a cut in which only highlights and shadows are printable by 'utilizing a resist of a line subject asy shown ln 8a, Fig. 3. It may also furnish a block in which only the shadows are printable, if the resist of the second stage in Fig. 3, is used as protection for the element of Fig. 4, to obtain pure whites. This last result, for a fine patterned ground, will be equivalent to a line cut.

A typical feature of the new cast products is that they are homogeneous, and that the projections representing the' values show the appearance of geometrically similar figures with truncated tops of diii'erent areas and clean edges which are developed in the moulding ground when the etching of the cavities is stopped by the unetchable bottom. This permits to identify a plate produced by the process because when projections are ground down to truncated s'tructures, as in some processes of the prior art, it is necessary to illl up the back in order to bring them to the same plane, while if the projections are nattened by pressure into an apparently truncated form they would show a somewhat' ways of the invention, these are also susceptible of modifications and substitutions within the scope of the achievement. It may beobserved,

for instance, that the diiference between the element presented in Fig. l, andthose of the other figures, is not merely the fact that the last are not sensitive to light, but that the etchable or dischargeable zones are insensitive, for the resistv transferred and developed on the insensitive ground would be equivalent to a sensitive coating that could be extended on it and suitably processed for the same purpose, and yet the discharge of matter would not be made from the sensitive but from the ynon-sensitive part of the element.

It may also be noticed that the simultaneous production of relief casting values and photoengraving printing values by the etching step in a suitable structure is independent of the means to selectively obtain it, as long as even light values thrown .on a ground covered with an etching solution may render this active or inactive and determine a. selective effect. It may equally be realized that the etching of metals described in the example ,is one of the many formsof discharging matter from a ground, which maybel built from other suitable substances susceptible of` being simply dissolved, or that the metals instead of attacked by an etching solution may also 4 be discharged by the electric current in knwn manner. l stratified an'd selectively etchable groundmay be combined both in a sensitive or insensitive 'element to produce raised values, Aall within the same fundamental idea.- And it'flnallymust be borne are relative within operativeness, for while the 4depressions should decrease in cross-sectional area for a ground of asingle substance, they need only to end sharply if a second substance at-their bottoni stops the discharge in depth; and that in the example of Fig. 4, for instance, where the printable they need not end demonstrate the invention, I believe to be new .v

and useful, and as such, I claim:

1. In a developable moulding element for a printing suiiface, a ground including a first thickr impermeable to 'and gradually solness of 'mat uble in a solvent, having on the upper side depressions or recesses sharply ending at the lower side, such depressions or recesses showing the reversed shape of a printable pattern corresponding to a high-light tint; and a second thickness of diiferent matter unetchable in land impermeable to Vsaid solvent adhered tothe lower side of the first thickness.

2. In a developable moulding element for a printing surface, two thicknesses of two different materials adhered to each other. the upper thickness corresponding to the casting side of the element showing a plurality of` small cavities decreasing in cross-sectional area from its surface and sharply ending substantially at the contacting area witht the lower thickness, such cavities forming a pattern having the reversed shape( of It may be' considered Ibesides that a' 3. vIn a developableV moulding element for a printing surface, three thicknesses of three different materials attached in superposition, the material in the upper'` thickness corresponding to the -casting side of 'the mouldhaving a plurality of depressions or recesses of the same depth substantially ending at theu contacting area of the first and second thicknesses, the respective-materials in each of these two thicknesses each soluble in a solvent in which the other material and that of the thirdthiclmess are substantially insoluble.

4. In an element developable into a mould for a printing surface a soluble ground carried by an insoluble support, said ground formed byseveral 'strata of different materials arranged insuccession,'each material soluble in" a solvent in which the other ones are insoluble, the outer stratum'l showing through its 'thickness' a. plurality of depressions corresponding to the reversed shape of a printing pattern for a tint.

5. In an element developable into a mould'for a printing surface,- a thickness of etchable matter' -having a. number of small cavities showing the reversed shape of a typographically printable pattern corresponding to a light tint, and means to modifylthe. extent of the etching at selected sections 4of said thickness -of matter, said means equally affecting every one of the cavities.

in mind that requirements in a given case p 6. In an element developableinto a mould for a printing surface, soluble matter forming a thick- 'ness having a plurality of minute depressions or-l recesses showing the reversed shape of a typographically printable pattern for a light tint, and insoluble second matter selectively distributed 4to modify the area of the soluble zones in the firstl matter, said second matter equally aiecting each .one of the depressions.

7.,In a developable moulding element for a printing surface, a thicknes's'of soluble matter `having a vplurality of small depressions or 'recesses showing the reversed shape of'a high-lightprintable pattern, and means to protect the soluble thickness, of matter at the outer surfaces in the spaces between the different cavities.

a. In a combined foundation developable by etching into a moulding element for a printing `surface reproducing a subject, a thickness of copmeability in' correspondence with the values of the subject. 1

a highlight printablesurface, said materials difo ferently reacting to asolvent in which the one of the upper thickness is gradually solubleand that oi' the lower thickness substantially insoluble.

of the etching at selected sections of said ground;

and means to proportionate the time of the etchv ing to the values of the subject at different areas of the ground. K l0'. A method of indirect photomechanical r production which comprises producing an etchable moulding ground characterized byj-'hav'lng on the casting side a number of small depressions or recesses showing the reversed shape of a highlight printable pattern; producing in known manner, transferring, developing 4and drying on said ground a negative carbon-tissue image of the original to be reproduced; etching the ground an'd cleaning and drying the resulting mould;

, ing it.

printing surface which corresponding to the casting side of the ground and characterized by having a number of minute cavities sharply ending at .the lcontacting plane of the two thicknesses and showing the reversed shape of a high-light printable pattern: then selectively etching said ground at different areas Afor different lengths-of time; and finally taking a cast from the resulting mould.

- 12. A method for the indirect production of a printing surface with pure whites which comprises making a. moulding ground by joining three thicknesses of different substances, two of which being soluble in different solvents and the third insoluble, the outer soluble substance corresponding to the casting side of the ground and characterizedby havingla plurality of small depressions or recesses endingat the contacting plane with the second lsoluble substance; selectively etching said ground in different areas for differentlengths of time with one of the solvents; re-etching the ground with the vsecond solvent; and'taking a cast from the resulting mould.

13. In the indirect reproduction oi' a surface the step of developing high-light casting values into half-tone and shadow casting values which comprises producing the high-light casting values in a ground, these values consisting in minute depressions or recesses decreasing in crosssectional area and sharplyending at the same plane; and then enlarging the cavities by discharging matter from the ground at diiierent areas in diierent proportions.

14. In'the indirect reproduction of a printing printing the upper thickness corresponding to the casting side of the mould showing a plurality of depressions or recesses decreasing in cross-sectional area,v and substantially ending at the plane of adherence of the two thicknesses, some of these depressionshaving a sharp bottom and some other ending in larger areas, the shape of these second depressions substantially corresponding to truncated forms of figures geometrically similar to the shape of the sharply ending recesses. said upper thickness supported by the lower thicknesswhich furnishes the bottom for the truncated depressions.

i8. In a.. mould for a printing surface, three thicknesses of matter in superposition and adhered to one another, the upper rst thickness showing a plurality of minute depressions or recessesl of which some are larger than the others, the smallest ones ending at the plane of contact of the rst and second thickness, and the larger. ones at the contacting plane of the second and third thickness, said second thickness representing the difference of depth oi the two kinds of depressions and correspondingly the difference in height of printing values in a cast taken therefrom, that difference being such that relief values corresponding in the cast. to the smallest depressions will be typographically unprintable andthe high-lights will be pure.

19. In a photomechanical printing element, a body of solid and continuous material of even thickness showing at the printing side a plusurface, the step of developing high-light cast ing values into half-tone and shadow casting values which comprises producing the high-light casting values' in a soluble ground, these values consisting in sharply ending cavities having their rality of small projections of different sizes decreasing in cross-sectional area, the smallest of said projections ending in sharp vertices corresponding to high-light'values, and the larger ones proportionally higher and ending in tops of greater printing areas, the outline of the larger projections substantially being a truncated form of a figure geometrically similar to the shape of the smallest ones, a characteristic of said projections being the clean intersection of the sides and tops of the figures.

' 20. In a printing surface, a body of solid and continuous material having on the printing side a plurality of minute projections of different sizes, decreasing in cross-sectional area and all corresponding I cally similar to the shape tions.

into casting values for .photomechanical values in surfacef which consists in first producing a ground having depressions or recesses decreasing in cross-sectional area and sharply ending at the same plane; providing in said ground means to protect the areas' under the bottom plane of the recesses; and then discharging matter from within said cavities atdifferent areas of the l ground proportionally to the photographic values.

16. In a mould for a. printing surface, a thickness of matter having a plurality of cavities decreasing-in cross-sectional area, a number of said cavities show-ing at-their bottoms minute graphic sections corresponding to .high-lightv values; 'and another number of cavities showing larger bottom values: the'cutline oithese second cavities substantially corresponding to truncated forms of. figures geometrically similar to the shape of thel nrst'cavities.

11. In a mould forfa printing surface. two thicknesses of material adhered-to each other.

height being such ending substantially at the same plane, some of these projections showing sharp vertices and the others larger tops. .the outline of the last to a form of a gure geometriof the sharp projec- 21. In a printing surface, a body of solid and continuous material showing a, number of minute projections representing whites and black values, and correspondingly having printing tops of diiferent sizes, the smallest ones representing the whites ending at a lower plane than the ones representing the black values, the difference in that the smallest projections will not print typographically and the whites will be pure.

22. In a. printing surface, a body of solid and continuous material of even thickness having a number of small projections with printing areas corresponding to high-light and tone values, these projections decreasing in cross-sectional area, having different sizes with correspondingly varied top areas, andfup to a plane passing by the vertices of the sharpest ones, showing all -the complete or truncated outline of geometrically' similar figures.

F. G. YANES.