US1952787A - Method of printing - Google Patents

Description

, March 27, 1934.. c. w. BENNETT 1,952,787

METHOD OF PRINTING Filed June 9, 1930 Bare meza/ fmu/sion Del 670,060 ,o/a/e Y CWBennett Inventor gr f Attorzzgy mafer/a/ (5/6/55) Patented ,Mar. 27, 1934 UNITED STATES 1,952,781 METHOD OF PRINTING Charles W. Bennett. Douglaston, N. Y., assignor,

by direct and mesne assignments, to Photo- Cast, Inc., Rochester, N. Y., a.

New York Application June 9, 1930, Serial corporation of -14 Claims.- (01. sis-5.6)

6 net consuming less time and less expense, than the methods used at present, thereby increasing efliciency.

With this and other objects in view, the invention resides in the novel steps and combinations of steps constituting the process, as well as the novel combinations of materials which enable the process to be carried out, all as will be disclosed more fully hereinafter and particularly pointed out in the claims.

Referring to the accompanying drawing forming a part of this specification Fig. 1 is an enlarged sectional view of a photographic plate with the developed emulsion thereon, and Fig. 2 is a view illustrating a stepin the casting of the printing surface, the casting metal being shown in contact with the builtup relief on the developed photographic plate. a

In order that the precise invention may be more clearly understood, it is said: The practice in use in the makeup of a newspaper will be discussed as being the most complicated case. Material entering into the makeup of the paper is received in a variety of forms including hand written, typewritten, and printed copy; photographs or other illustrative pictures or diagrams; and flat plates. The latter may be ethed plates, electros, or casts either negative or positive, made from these. The above mentioned copy is then set up in type, in the form of justified lines to make a column, by hand with individual type, or by a machine which furnishes a castingof a line as a unit which lines are then assembled into a column by hand. Illustrative pictures or diagrams are first made in the proper size plates ethed in relief which, with the other previously named forms of material for newspaper makeup (always of course in positive form) are worked in with the type columns to make up the page form, and from this form the ultimate printing surface is produced.

With such a method as'has been described, it is apparent that all copy must be typographicall'y transcribed by the type-setter, thus necessitating page, .and hand type-setting is extremely slow,

and therefore expensive. Illustration, by the use of photoengravers blocks, is too expensive and time-consuming for the purpose served. Furthermore, since all the material used in this form of block is a total loss after the impression is taken for the matrix, conservation requires a substitute method of illustration if such is possible. Y

In the invention now to be described, all of the above objections have been overcome. That is to say, I have discovered that the makeup of a newspaper for instance, can be advantageously and economically accomplished by a method which can be operated to release from the plant all the type and type metal which is today required.

In the first place, it may be said that this method of printing is to be done on present equipment from relief plates. Heretofore, relief plates have been, and now are, prepared by protecting the relief parts of a plate, while the intervening space is removed by solution of the plate material in a solvent, or by actually removing the metal as such, by grinding, chiseling, or cutting, which is 'amethod found quite expensive due to the utilization of high priced metal. The universally used method of etching or dissolving the metal is open to the objection that much time is consumed in preparing plates since the protection of tht relief parts requires plural operations. In other words it becomes necessary to protect the sides of the relief to prevent undercutting during the progress of the relief formation since said undercutting spoils the fineness of the work, and there is no known means of replacing the material once it has been removed.

Relief, of course, is a question of relativity, and it is a matter of first principles that it may be obtained by excavation of one part while another is held in the original level, or it may be obtained by holding one part in the original level while the other is built up. Duplicates of relief surfaces have been prepared in both ways heretofore, but my invention allows the preparation of the original by the building-up method on a plane resistant surface, which has not heretofore been accomplished. Furthermore, by means of a 100 combination of processes photographic and mechanical, my process allows thetransfer of any succession of characters or images, delineated by color difference or contrast, to a relief surface in which either the one or the other (that is either the light or the dark portion as desired) may be raised in relief as compared with the other. In other words, my invention connotes the transferal of color relief to physical relief, by building up one or the other part.

The first step in my process is the makeup of the matter entering into the sheet or page of form to be printed. This is done in full page sizes or in parts of apage, in columnar form, for the preparation of a finished page later, as the exigencies of the situation require. The makeup may be exact size, but I have found better results are obtained if the size is one-and-one-half or two times the required final size. The makeup is, therefore, in the size of type necessary considering the reduction and is a duplicate of the work to be printed save for size, the text or reading matter being assembled in correctly readable justified lines in columnar form.

I may now assemble the 'textas above produced. This is arranged on a large easel or board which is fitted with grooves to hold black columnar strips dividing the text page into units of columns, whose widths may vary as occasion demands. The columns may be broken at any line by simply cutting the paper or other material holding the printed word as a result of which a part of an item may appear on one page and another part on a different page'of the paper. In this way, the text may be shifted through several editions of the paper if desired. Advertisements may be set in a similar way, where standard characters only are required and headlines and subheads may be treated likewise. Where special type is required, photographic machines are available for recording directly a large variety of type in various sizes. Such positive records, I use in the makeup of the newspaper page, or its parts along with the type impression or record of text.

For the sake of description, I provide an easel or board, say twice the dimensions of the desired newspaper page for assembling the makeup. With such a s'ized board the text used, as well as the matter set up by one or more of the photographic machines, must be of twice the dimensions finally desired since, as will appear later,.-the matter fromthis makeup board is to be reduced in size for the final printing record. Any advertisements in the form of photoengravers blocks, or syndicated material in the form of boiler plate, or flat stereotype, are handled by taking a proof on the paper I use in the makeup of the page. These proofs which are in units of columns in width, are secured to the easel along with the aforementioned text. If the syndicated material etc. is of the proper size for the paper direct, space for this material may be left on the easel, the actual blocks or boilerplate for this omitted material being used in a later stage of the process, as will be pointed out hereinafter.

Illustrations in the form of, original diagrams, line drawings, maps, etchings, or the like are used direct on my makeup easel along with-the material discussed above. Halftones in the form of positives are handled directly in theabove makeup. These are made by the photographer. with a camera which has a screen interposed between the lens and the plate or film. If the pictures are twice final size and a-60 line halftone is desired, the photographers screen will be a .30 line screen. Ordinary photographs may be used'in my makeup, but they are-not desirable as being more difiicult to handle as will appear later. These are handled directly and with facility, in my sectional makeup ,as will appear below. It is pointed out that whathas been said above applies to the makeup in full page form only,

and that the problem becomes more flex ble when parts of the page are considered under this stage of the process. In the full page size I use any and all material in positive form, 1. e. as a positive proof or print that goes into the makeup of a paper today, with the exception of ordinary photographs, which are handled with difficulty.

I have now assembled the text page on an easel, the surface of the work in one horizontal plane, with the text in the form it will appear when printed. By this method the text page may be hand embellished while on the easel, so that it may appear at its best upon reproduction. This is impossible in the makeup used at present.

The easel is now mounted before a camera, with the proper lights playing on the page makeup. The camera may contain a film for the production of a negative as is well known in the art of photography, but I have found it preferable to substitute therefor a metal plate sensitized with an emulsion, of the bi-chromated gelatine variety,'a. prism being used to reverse the image of the page on the plate. The metal of the emulsified plate may be steel, zinc, copper, aluminum, their alloys, or any metal with a plane surface which will hold the emulsion without scaling when dry, or without disturbing reactions while wet. The metal may have a polished surface, or the surface may be grained, as is now the case in the preparation of offset plates, the emulsion being spread uniformly over said surface, and dried.

The emulsions used at present are all too slow, in printing or exposing time, to serve the purpose of quick work, so a faster sensitive combination is required. This has been found in the following compositions:

. Parts (1) Gelatine 4 Chromic acid /g Strong ammonia 26 degree) 1 Water 240 Parts (2) Gelatine 17 Chromic acid; 3% Strong ammonia (26 degree) 2 Water 240 which produce an emulsion requiring in' time an exposure to light which is from one thirtieth to one fiftieth of the time required for the bichromated emulsions heretofore used or suggested. In other words, emulsions (1) and (2) are thirty to fifty times faster than those used heretofore. If emulsion (l) is used, the plate after exposure in the camera is inked over the entire emulsion surface, and then developed in water. If emulsion (2) is used, the plate may-be treated in the same manner, or it may be developed in water first and then dipped into a solution of an aniline dye so that the exposed portions are marked out in color as compared with the unexposed parts, the latter parts appearing as bare metal, practically. That is to say, the black letters or characters of the page makeup on the easel appear on the developed plate as bare metal, while the white parts of the page makeup (that is the parts of the paper strips not covered with characters.) appear on the metal plate as the parts of the printed emulsion as clearly shown in Fig. 1. These parts will appear as inked surface, or as dyed with aniline dye. The image appears on the plate exactly as it was on the page makeup save that it has been reduced to the proper page size by the proper arrangement of the camera.

' and the background the ink or the dye, marking as much as fifty degrees centigrade by the addition of three or four per cent of lime, for instance; To accomplish the addition say' of rosin or lime hardened rosin to the background, the

. plate is first dried, then dipped in powdered rosin or lime hardened, rosin, or the powdered material may be sifted over the plate. The excess is knocked off and the powder will be found to have stuck selectively to the inked surface. This melted in, by heating the plate.

While the plate is still hota non-melting 'material, that is a material which does not melt under the conditions, is applied to the plate as was the rosin, and further heated into the rosin ink base. I have discovered that powdered glass, or metallic oxides such as litharge, alumina, and the like are suitable for this stage of the process. I have discovered that the product from a Cottrell precipitator in the stack leading from a furnace burning powdered coal is excellent for the above purpose. This material is an ash or glass containing silica, alumina, and iron oxide. It is very fine in grain size, approximately one half passing through a 500 mesh screen thus making it admirable as a powdered material, and it is cheap, being a waste product. For some types of work, these two additions will be found to furnishsuflicient relief, and the treated plate would appear in cross-section as indicated in Fi 2.

Where more reliefis desired, the top surface is re-inked and the process repeated. The reinking is done either wet or dry, depending on the character of the work, and the quality of the ink used. I have found that various gums and balsams may be substituted for the ink, with the result that the pickup of powdered material is greater. Commercial fiexoresins, Canada balsam, and other sticky materials have given good results. The relief can be made as much as dematerials. The powdered materials may vary from rosin to powdered metals, through a range of softening points, flow points, and hardnesses.

.For instance, powdered metals such as iron would consists in the building up of an image supplied photographically from color contrast, as compared with prior processes which require a glycerine image to be. built-up. The latter must be supplied by hand, or the character must be had in relief originally for printing the glycerine image. Prior processes are essentially duplicators of charactersalready had in relief, while my process allows the preparation of the original relief from color characters not yet predetermined in physical relief.

Also my process is susceptible to a dual control, making it even more flexible than the etchmg process.

To illustrate, suppose in building reliefs by my process upon a copper plate, the built up part extended too far into the open parts, or in other words, the lines became too narrow, and hence filled. I then protect the top of the relief with a suitable agent such as ink, ba1sam,.or topping powder, and subject the relief to an etching agent, incapable of attacking the supporting copper plate, in order to etch the sides of the lines to clear. The etching agent must dissolve the bulk of the material of the relief, and the resist on the top (as well as the material of the supporting plate) must be insoluble in the etching agent. That is to say, for rosin or lime hardened rosin, the etching agent may be alcohol, and the resist or protection on the top of the relief may be collodion or gelatine, or such protective films which are insoluble in alcohol. I desire great latitude in the selection of the etching agent, as this agent will vary with the selection of the building up powder. This is also true of the film protecting the top of the relief, since this must vary with the etching agent.

From the above discussion, it becomes evident that my process allows the filling of the lines if desired, by using a powderedmaterial which will flow upon heating, and heating to the desired point; the clearing of these lines if they should fill, or opening them if they are'not open enough; I

and finally the building of the relief higher by reversal of the plate during heating. In other words, the process is more flexible than the etching process, since the latter offers no possibility of changing the width of the lines without damage to clearness or sharpness. It isto be remembered that my image is first laid down as shown in Fig. 1 in a reasonable thickness of insoluble gelatine, which preserves the sharpness throughout.

For the sake of simplicity and clarity, I will follow this relief plate through to a conclusion. When the proper relief has been obtained, the plate is ready for the next stage of my process. In determining the required relief, it is not always economical to build up to fit the maximum relief required on a page of a newspaper, the relief being built up to suit the majority of the matter on the page. Then the plate will go to an operator who will supply the needed relief on the wide open parts. This I do with strips of gummed pasteboard, which are quickly worked into the open spaces for a relief of a quarter of an inch if desired. Thus it is evident that a relief of from four to nine thousandths of an inch .is all that is necessarily required for my process, although it is pointed out that any desired amount may be economically had if desired.

After the wide open spaces have been taken care of as'to relief, the plate is ready for the flat stereotyping process, which consists of making 'a flat stereotype cast of the relief surface as indicated in Fig. 2. This stereotype is the printing Percent Bismuth Lead 2'7 Tin 13 Cadmium 10 a metal of extreme hardness and great crushing strength is obtained, with a melting point of substantially '70 degrees centigrade. The use of alloys greatly widens my choice of a building-up powder. However, I do not limit myself to combinations melting below the boiling point of water, for with lime hardened resin and powdered glass in the form of the Cottrell precipitate, it is clearly obvious that a relief can be obtained that will allow of casting my fiat stereotype in type metal.

The image is transferred directly to the metal, for which I claim practical novelty, in that an emulsion has been discovered with sufficient speed so that it may be exposed or printed by the meager light obtained through the lens of a camera. Heretofore this has required the matter of an hour printing time, while I do this in one to three minutes. Or, the image is transferred to the metal through a negative by projection or' contact printing, which is believed novel in combination with other steps of my process. This image is taken in a novel way from a magnified page makeup in black and white on a special easel, the advantages being that not only can the operator see how the page will look before it is in the press, and make readily any corrections, changes, or hand embellishments, but, all of the materials that go into the makeup at present can be used. Further, type can be discarded, much of the metal now tied up in a plant can be dispensed with, the operation is speedier, and expensive skill is largely removed from the process.

Mention was made in the above concerning the use of an ordinary photograph in my page makeup. It is simpler not to attempt this as some means must be provided to break up continuous surfaces so that the ink used in printing will be distributed to give at least as good a reprodiiction of a photograph as is obtained today with the present means. This breaking up of the continuous surfaces may be accomplished by placing a screen on top of the sensitized emulsion on the metal. plate. This would introduce difficulties with small pictures, and necessitate the placing of the screen over a part of the plate, and also introduce difliculties of time of exposure. Therefore, I prefer to handle the photographic illustrations' which are now used as halftones separately in the following way. l v

Now in actual newspaper practice, there are few pages that can be made'up as a whole. The material in some parts of the page must be kept subject to change, or in a mobile condition. On this account the majority of the pages of the paper are and should be made up in sections, a practice to which my process lends itself admirably.

' During the day, as material is released for the form as it appears now, this material is made .up

in relief plate form, the width being in-columns, and the length being dependent on the amount of material released. Flat stereotype of this gives the relief plate in the form of the present boiler plate", which can be worked into the page makeup form preparatory to making the matrix. In other words, I can make up the whole page on the easel, and transfer that, or I can transfer any part of the page to a relief plate and finally to a fiat stereotype in" the form of the present boiler plate, which is mobile. This boiler plate is then assembled and locked into a form just as it is at present, for the final matrix and curved stereotype plate.

Some advantage is gained by splitting up the page in this way, for the work can be spread out over the day as is the usual custom, and by doing the relief work in sections, the character of the work as to requirements for relief can be kept more nearly uniform for one plate. For instance, a plate would be run through containing halftones of one screen size, another of text of uniform type size, while still another would contain advertisements with wide open spaces, calling for high relief. handle full pages or any parts of a page, as the necessity of the case demands. The resulting flat stereotype may therefore be a full page, or in the form of columns to be assembled into page form for matrix making. The latter form allows of changing the makeup of the page through the various editions of the paper, without the necessity of remaking the whole page.

While in the above I have described a practical means of building-up the plate to relief by actual physical accretion of materials, I do not wish to be limited in the practice of my inven tion to such means. In fact I have discovered that various physical and chemical means may be utilized for obtaining relief, and these I consider an important basic principle of my invention.

By way of illustration a method of bringing the printed image into relief consists of raising, or rather pufiing up the printed film or a film of another material added thereto, with gas. To raise the whole surface of a newspaper page 5/1000ths of an inch requires 17x23x5/1000' inches, or about 2 cubic inches, of gas. This volume of gas is furnished by 0.25 gram of sodium bicarbonate'in going to sodium carbonate.

'The printed film I use may be thick enough to form a matrix for several times this volume of gas over the surface of the page measuring 17x23 inches. The film can carry more than sufficient bicarbonate to furnish this gas upon heating, or the gas may be liberated chemically. The dried print is soaked in sodium carbonate solution, whirled dry, and an aluminum sulphate solution added to the plate. The gelatine of the film protects the alumina precipitate which entangles the gas and holds it, raising the film.

' A compound, losing or giving up a gas at low temperature, may also be incorporated in the printed image. Potassium bicarbonate loses carbon ,dioxide at from 100-200 degrees C., and if this material is placed in the printed portions by soaking in a strong solution of the salt, and the plate heated, the film will be blown or puffed up to relief. Other carbonates including the ammonium carbonates may be. used for this purpose. a

My process practically then will Another reaction that has been used for the purpose as above described is-the reaction of chromic acid which is already present in the film,

with oxalic acid. Or hydrogen peroxide may be used to furnish gaseous oxygen. Both of the above liberate oxygen which raises the printed parts in relief.

Another method is to place the wet developed plate in a gas atmosphere under high pressure,

say 500-1000 pounds pressure to the square inch,

allow the film to take up the gas, and then suddenly release the pressure. The printed film will be found puffed up to relief.

Several variations of the film may be made. For instance, by rolling the print up with ink, as done in engraving, a rosin topmay'be obtained over the gelatine. This film may be raised for relief as well as the original printed image. Or a film of rubber may be placed over the entire plate and the printed image, or this plus a rosin or other substance such as gum arabic, be raised with rubber. The rubber covering the bare metal remains in place, while that portion covering the printed image is raised in relief. The rubber may be deposited as a film from a latex solution, or from a solution of the rubber in a solvent such as benzol or mineral spirits. The rubber may have incorporated therein sulphur and an accelerator so that the vulcanization can be carried on for the production of a desirable surface against which to make the casting for a flat stereotype.

In the use of the above named methods of raising the printed film with gas, it is desirable to have the fihn more plastic than that used in the other methods of obtaining relief. The gelatine may be plasticized by the addition of glycerine and gum arabic. I have developed the following sensitive or printing emulsions for this purpose.

Parts (3) Gelatine 10 Gum arahin Glycerine 10 Potassium chromate 2 Chromic acid I Stpong ammonia Water- 150 Parts (4) Gelatine 7 Gum arabic 7- Glycerine Potassium chromate Chromic acid 3 Strong ammonia 2 Water 220 Films of varying degrees of plasticity are obtained by using mixtures of varying amounts of the-above formulae (1) (2) (3) (4).

I have also discovered that it is economical to use more time in the makeup of some newspapers, and less time in the printing of the paper. This speeding up of the printing operation with present equipment is made possible with my page assembly. That is to say, the page makeup on the easel is the essential starting point, and then the image is transferred to the metal direct in the camera or by projection or contact printing through a negative, so that the proper imageis had on the metal. The metal is then etched in relief and, by means of theproper clamps and holders, used directly on the rotary press for printing. In this way the speed of the press can be doubled, due to the lightness of the plate. Of

course if the whole paper is printed thus, the unit is the page, and my page assembly makes this possible. In this case I use a built-up plate of halftones for the production of the flat stereotype, to produce a. positive proof, which is included in the page makeup for the etching proces of producing a light printing plate.

I do not wish to be limited in the application of my process to the use of any one of the above mentioned means of building-up the relief, since it may be economical to use two or more of the above mentioned methods in the production of one plate. I also wish to be free to combine my building-up methods, with etching methods for the production of a practical plate. To illustrate, in order to obtain-sufficient relief to allow the application of a binding material selectively to the printed image and not to the bare metal, I have flowed my emulsion over a uniform film of rosin, for instance, previously applied to the metal plate.

After this is printed or exposed and developed, the rosin is etched down to the face of the metal. In this way, sticky binders or even water and such liquids may be selectively applied to the image to be built-up. If the work is of such a character as to give a very unevenv etch of the rosin, to the end that an imperfect printing surface is obtained on the fiat stereotype produced therefrom, the fiat stereotype may be shaved the thickness of the rosin film for a perfeet reproduction of the print. I do not wish to be limited to the use of rosin for the purpose above mentioned, since there are many materialsthat will serve as a lifting film for the emulsion, and may be;etched with solvents which do not affect the printed film, or may even harden it as does alcohol in the case of the rosin etch.

It is obvious that those skilled in the art may vary the details of construction and arrange characters of the make-up appear as bare portions of said support; applying to the covered portions of said support a material capable of liberating gas together with a vehicle capable of entrapping the gas when liberated; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

2. The method of producing a printing surface which consists in establishing a positive copy make-up; photographically exposing a bichromated type sensitized surface of a plane support to said make-up; developing said surface to obtain an image of said'make-up wherein the characters of the make-up appear as bare portions of said support; applying to the covered portions of said support a material capable of liberating gas together with a vehicle capable of entrapping the gas when liberated, said application being made to the surface of the covered portions; liberating gas from said material, whereby increasedrelief is obtained; and producing the gas together with a vehicle capable of entrapping the gas when liberated, said application being accomplished by immersing said covered portions in said material or a solution thereof; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

40- I V ated; liberating gas from said material, whereby face which consists in establishing a positive copy vehicle capable of entrapping the gas when lib- 4. The method of producing a printing surface which consists in establishing a positive copy make-up; photographically exposing a bichromated type sensitized surface of a plane support to said make-up; developing said surface to obtain an image of said make-up wherein the characters of the make-up appear as bare portions of said support; applying to the covered portions of said support a material capable of liberating gas by chemical decomposition together with a vehicle capable of entrapping the gas-when liberated; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

5. The method of producing a printing surface which consists in establishing a positive copy make-up; photographically exposing a bichromated type sensitized surface of a plane support to said make-up; developing said surface to obtain an image of said make-up wherein the characters of the make-up appear as bare portions of said support; applying to the covered portions of said support a material capable of liberating gas upon application of heat together with a vehicle capable of entrapping the gas when liberincreased relief is obtained; and producing the printing surface from the bare portions of said support.

6. The method of producing a printing surmake-up; photographically exposing a bichromated type sensitized surface of a plane support to said make-up; developing said surface to obtain an image of said make-up wherein the characters of the make-up appear as bare portions of said support; applying to the covered portions of said, support a material capable of liberating gas through a chemical decomposition and application of heat, said application including a erated; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

-'I. The method of producing a printing surface which consists in establishing a positive copy I I make-up; photographically exposing a bilchromated type sensitized surface of a plane support to said make-up; developing said surface to obtain an image of said make-up wherein the characters of the make-up appear as bare portions of said support; subjecting the wet developedsurface to a gas atmosphere under high pressure for absorption, and then suddenly releasing said pressure,' whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

8. The method of producing a printing surface which consistsin establishing photographically,

ocate? an image of a subject on a support sensitized with an emulsion of the bichromated type, said image consisting of bare and covered portions of said supportfapplying to the covered portions of said support a material-capable of liberating gas together with a vehicle capable of entrapping the gas when liberated; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

9. The method of producing a printing surface which consists in establishing photographically an image of a subject on a support sensitized with an emulsion of the bichromated type, said image consisting of bare and developed emulsion portions 'ofsaid support; applying to the developed portions of said support a material capable of liberating gas together with a vehicle capable of entrapping the gas when liberated; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of /said support.

10. The method of producing a printing surface which consists in establishing photographically an image of a subject on a support sensitized with an' emulsion of the bichromated type, said image consisting of bare and covered portions of said support; applying to the covered portions of said support a material capable of liberating gas together with a vehicle capable of entrapping the gas when liberated, said application being made to the surface of the covered portions; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

11. The method of producing a printing surface which consists in establishing photographically an image of a subject on a support sensitized with an emulsion of the bichromated type, said image consisting of bare and covered portions of said support; applying to the covered portions of said support a material capable of liberating gas together with a vehicle capable of entrapping the gas when liberated, said application being accomplished by immersing said covered portions in said material or in a solution thereof; liberating gas from said material, whereby increased relief is obtained; and producing the printing surface from the bare portions of said support.

12. The method of producing a printing sur-' face which consists in establishing photographically an image of a subject on a support sensitized with an emulsion of the bichromated type, said image consisting of bare and covered portions of said support; applying to the covered portions of said support a material capable of liberating gas by chemical decomposition together with a vehicle capable of entrapping the gas when liberated; liberating gas from said material, whereby increased (relief is obtained; and producing the printing'surface from the bare portions of said support. A

13. The method of producing a printing surface which consists in establishing photographically an image of a subject on a support sensitized with an emulsion of the bichromated type, said image consisting of bare and covered portions of said support; applying to the covered portions of said support a material capable of liberating gas upon application of heat together with a vehicle capable of entrapping the gas when liberated; liberating gas from said material;

. 1,952,787 ducing the printing surface from the'bare por-' tions of said support; applying to the covered portions of said support a material capable of liberating gas through a chemical decomposition and application 01! heat, said application including a vehicle capable of entrapping the gas when liberated; liberating gas from said material;

whereby increased relief is obtained; and producing the printing surface from the bare portions 01' said support. a

. CHARLES W. BENNETT.

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