US2596115A - Screened positive for use in preparation of intaglio printing plates and method of making said positive - Google Patents

Description

May 13, 1952 L. c. AUSTIN 6, SCREENED POSITIVE FOR USE IN PREPA ION OF INTAGLIO PRINTING PLATES AND METHOD OF MAK SAID POSITIVES Filed Dec. 26, 5

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SCREENED POSITIVE USE I REPARATION OF INTAGLIO PRINTING PLATES AND METHOD MAKING SAID POSITIVES Filed Dec. 26, 1945 2 SHEETS-SHEET 2 5 r- F915 5 57 55 lK/OZAET I 0 g 55 55\ 7E F19 Z5 F1911 F914- INVENTOR.

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ATTOR/VEKS Patented May 13, 1952 UNITED STATES PATENT OFFICE SCREENED POSITIVE FOR USE IN PREPARA- TION OF INTAGLIO PRINTING PLATES AND METHOD OF MAKING SAID POSITIVE 4 Claims. 1

My present invention relates to intaglio or gravure printing forms, and to methods and apparatus for producing the same. More particularly my invention relates to improved photogravure printing forms adapted for modern high speed long run printing operations, which may be produced with less skill than the prior forms, and which provide prints of better tone and color value than it is possible to produce with the prior photo-gravure processes commonly used in high speed commercial printing operation.

As is well known, in the usual type of rotogravure printing positives have a tonal range of from about .3 to 1.6 by densitometer reading. Thus although these readings fall short of a full range as applied to photo-engraving or photolithography the nature of the next step in the process of gravure pigment paper or carbon tissue results in the production of etchings or printing forms full scale screen formation is utilized in which the ink is retained in substantially square wells or pockets of uniform area each separated from the adjacent wells by thin metal walls, the outer surfaces of which support and are wiped free of ink by the doctor blade of the press in printing operation. In such forms the walls of the wells are etched at an angle of approximately 45 degrees to the wiping edge of the doctor blade which is parallel to the axis of rotation of the printing cylinder or form. The varying tones of the print are secured by etching the ink receiving wells to differing depths, with barely perceptible wells in the absolute high light areas, and wells increasing in depth from the high light to the deepest shadow areas. The constant rubbing or wiping of the doctor blade against the flush outer surfaces on such etchings results in friction and wear, which, particularly at higher printing speeds and in long printing runs, may make replacement of worn cylinders or forms necessary before completion of the run, with no certainty that the etched replacement cylinder or form will conform with sufficient accuracy to the initial form, particularly in color work where accurate registration and duplication of tone values of the different color etchings is essential for satisfactory printing.

A further difficulty in the use of the prior rotogravure printing forms is that the individual etched wells are substantially U-shaped, and if the etching is not carefully done the etching fluids undercut the well outlet periphery. As a result the full complement of ink is never drawn from either of these well shapes in the printing operations. This at times requires excessive depth of etching to secure reasonably satisfactory prints at commercial printing speeds and results in loss of tone values in the dots due to the fact that the ink deposited on the print is not accurately controlled by the well size and shape.

As the speed of printing is increased with such etchings, the quality of the print progressively deteriorates, particularly when modern high speed quick drying inks and ink fountains are used. This is due to the tendency of the ink to pull out of the cells under the wiping action of the doctor blade, and to the diminishing quantities of ink withdrawn from the wells as the printing speeds are increased. This results in further destruction of print tonal values and limits the printing speed of the usual rotogravure process.

In efforts to overcome the foregoing difficulties encountered in high speed long run printing with the usual rotogravure printing forms and methods, several printing forms have been developed in which tone variations are secured by etching separated substantially square ink receiving pockets or wells of varying areas, essentially U-shaped in section and substantially uniform depth in general checkerboard pattern so as to deposit dots of ink of varying size on the printed surface. The tone differences are secured with such etching by depositing the largest dots in the shadow areas and the smallest dots in the high light areas of the print. The checkerboard pattern is particularly evident in the middle and lighter tones in which the substantially square wells are. separated by substantially square unetched metal surface areas. Such etchings are commonly referred to as dot-size etchings.

They are formed by use of screen positives made by suitable exposure of a full tone negative of the subject through a half tone screen, and embody a short scale screen formation in checkerboard arrangement due to the effects of light diffraction by the screen. In a full scale screen formation the space between the dots is a minimum in the shadow tones, while in a short scale screen formation the space between the dots is larger and the dots are correspondingly smaller in the shadow tones. Because of their checkerboard pattern, and variation in dot sizes to provide tonal effects, they have substantially greater metal areas between the printing wells for the support of the doctor blade, and accordingly provide more durable printing surfaces than the fully etched screen formation gravure etchings. The short scale screen formation increases the tendency to print the screen pattern, and this also gives especially in the shadow tones a lack of distinct tonal values in dots only slightly different in size due to the large non-printing metal surface areas which prevents satisfactory printing in modern high speed rotogravure presses due to excessive loss of tone values in the print.

To overcome the foregoing deficiency of the dot-size forms in high speed printing, etched printing forms have been developed which, in addition to the checkerboard pattern, and variations in area of the ink receiving wells of the dot-size forms, embody variations in depth of the wells to add improved tonal value over the dot-size etchings. This form of etching has gone into successful use in multi-color high speed long run rotogravure printing. Such forms are commonly known as dot-size dot-depth etchings and are successfully used in the commercial multi-color rotogravure printing for long runs on modern high-speed presses. Like the dot-size etchings, the dot-size dot-depth etchings embody short scale screen formation and U-shaped wells which lack separate and distinct tonal values and form literally half tone images, the shadow tones starting a little below the middle of the regular screen plate scale.

The dot-size dot-depth process provides no improved printing values at low speed over the usual photo-gravure process and is therefore used only for high speed color printing. Both the dot-size and dot-depth etchings have so much non-printing area that lack of tone in the prints is evident at high printing speeds. While the dot-size dot-depth etchings provide about 25% more tone scalethan the dot-size etchings, the dot-size dot-depth prints fall short of the full tone scale attained in the usual rotogravure process, and even the dot-size dot-depth etchings are therefore useful only for high speed color work.

The regular gravure process provides the longest period for properly completing the etching and thus provides a maximum degree of control. This period is from about twenty-five to thirty minutes. The dot-size processes provide the shortest etching period of from about three to nine minutes, giving the least control of the etching. The dot-size dot-depth etching period, and consequently the control provided, is intermediate the regular gravure and dot-size processes, and extends from about eleven to fourteen minutes.

To produce commercially acceptable prints by any of the foregoing processes requires considerable skill in the various stages of preparation of the printing surface including considerable retouching, much of which is done on the positive image and will often increase from 1.7 to 2.5 the densitometer reading of a good regular rotogravure positive. And when the positive is retouched it loses its value of standard density range for the subsequent workers.

The normal process of rotogravure requires use of a pigment paper print from a common gravure screen at forty-five degrees for monotone work. In usual rotogravure multi-color printing adifferent screen angle is used for at least the three darker of the four colors, to effect a slight relative displacement of the deposited color dots on the print and prevent moire screen formation on the composite print.

The dot-size dot-depth process in use for color work requires the special skill of very well trained above average workers previously experienced in the production of the usual rotogravure multicolor etchings and photo-engravings. To produce such etchings requires use of screen positives with the shadow tones starting a little below the middle of the usual screen plate scale. To correct color deficiencies and to extend the short scale screen positive, continuous tone positives are used in conjunction with the screen positive which must be under scale photographically compared to the usual gravure continuous tone positive. These are in turn over-retouched to correct photo-color defects and also defects due to lack of scale in the screen half-tone positive. The retouching on some of the continuous tone positives for this method often extend up to opacity the limit of the densitometer reading, to give the fullest possible effect in correction of tone values for etching in what is literally only a half-tone process.

A primary object of my present invention is accordingly to provide an improved intaglio printing form of the dot-size dot-depth type in which the advantages of improved full scale screen coverage area formation plus the softness of tone range of the best kind of continuous tone positive for producing the finest regular roto gravure etching, with improved tone values in the prints, are secured and the foregoing disadvantages of the prior photogravure etchings are minimized or eliminated.

A further object of my invention is to provide improved intaglio or gravure etchings, and processes of and apparatus for producing the same, whereby higher quality gravure prints are produced in longer commercial high speed runs.

A further object of my invention is to provide novel intaglio etchings having separated minute ink receiving wells of varying size and depth, depending upon the tone values, and in which the individual wells have their maximum areas at the printing surface of the etching and decrease in area from the surface inward in a manner permitting complete removal of all of the ink from each printing well during each printing operation regardless of the nature or consistency of the ink. This provides separate and distinct tone values and each different size of dot with tonal values and quality of print not heretofore obtainable with any prior photo-gravure etching. With my improved etching it is possible to reproduce the deepest shadow of a subject with shadow detail the finest high-light tones and detail, in modern high speed printing operation in a manner not heretofore attainable.

A still further object of my invention is to provide an improved dot shape dot size and depth process which is substantially like regular rotogravure etching in procedure, but in which tonal control of the positive dots is secured through shaping of the etched cavities, not attainable in any other known intaglio screen process.

Another object of my invention is the provision of processes and apparatus for the production of improved dot-size dot-depth screen positives in which each size of dot, from the deepest shadow to the finest highlight has a separate and distinct tone value.

A further object of my invention is the provision of a dot-size screen positive in which each dot has a central core of maximum density and decreases in density to the periphery of each dot, and in'which the dots are of substantially square full scale screen formation, rather than the usual dot-size checkerboard dot arrangement.

Still another object of my invention is the provision of a novel screen positive of a subject in which the image is made up of separate dots which vary in size to impart tonal values to the image with the largest dots in the deep shadow tones and the smallest dots in the highlight tones, and in which each dot increases in density from its periphery to a central core, and each dot from the deepest shadow dot to the smallest highlight dot diminishes in tone value as it diminishes in size.

A further object of my invention is to provide an improved photographic screen positive comprising dots of differing sizes and tonal values separated by transparent areas in which the tonal values. increase from a minimum in the highlight tones to a maximum in the deepest shadow tones, and having the tonal range of a regular rotogravure positive as established by densitometer readings.

In the prior processes color correction is necessarily made by retouching the positive used to produce the etched surface. This procedure is subject to uncontrollable variations due to the human equation introduced, and is the definite cause of lack of ability to standardize the etchings produced. Another object of my invention is the provision of improved screen positives for the production of photogravure etchings which need not be retouched for printing and can therefore be made standard in tone reading, and for the first time permit the use of predetermined etching acid formulae to provide predetermined tones in the prints, thus enabling uniform high grade etchings and resulting high grade prints to be secured with workers having considerably less skill than at present required for any of the known photogravure processes.

A still further object of my invention is the provision of improved camera screen and stop arrangements and novel methods of utilizing the same in the production of improved high grade photogravure screen positives with a minimum use of skilled workers.

Still further objects of my invention will appear from the following detailed description of the preferred embodiments thereof and from the scope of the appended claims. As shown in the drawings:

Figure 1 is an enlarged diagrammatic illustration of a tone scale.

Figure 2 is an enlarged fragmental diagrammatic illustration of a usual type of rotogravure screen;

Figures 3 and 4 are fragmentary diagrammatic sectional and plan views illustrating in enlarged size the shape of the ink receiving wells in an etched photogravure cylinder or printing form of the usual type;

Figures 5 and 6 are fragmentary diagrammatic sectional and plan views illustrating in enlarged size the ink receiving wells of a prior dotsize etched photogravure cylinder or printing plate resulting from practice of the process of U. S. Patent to Stirling, Number 1,773,887.

Figures 7 and 8 are similar fragmentary diagrammatic sectional and plan illustrations of a prior dot-size dot-depth photo-engraved printing cylinder or plate resulting from practice of the process of Dultgen Patent No. 2,096,794;

Figure 7A is a diagrammatic sectional view of the plate of Figure 8 in final form;

Figures 9 and 10 are similar diagrammatic fragmentary sectional and plan views of an improved corona tone dot photo-engraved printing form of the present invention;

Figure 11 is a diagrammatic illustration of a preferred camera, stop, and screen arrangement for producing the screen positive used in etching my improved corona tone dot printing form or plate of the character illustrated in Figures 9 and 10;

Figure 12 is an illustration of a usual form of stop used in producing dot-size screen positives;

Figures 13, 14 and 15 are illustrations of preferred forms of stops utilized in producing the improved corona tone dot negative of my present invention;

Figures 16 and 17 are fragmental diagrammatic illustrations of screen formations used in producing my improved screen positive.

Figure 18 is an illustration of the completed dot formation of my improved screen ,positive.

Figures 19, 20 and 21 are illustrations of the effects of the exposures with the stops shown in Figures 13, 15 and 14 respectively.

In Figure 1, I have illustrated as a subject for each of the etchings hereinafter described, a tone scale embodying a deep shadow area 22, a medium tone area 23, a highlight area 24 and an absolute highlight area 25.

In etching the regular rotogravure printing form an image of the usual screen 26 (Figure 2) is first printed on the sensitized pigment resist. Such a screen consists of uniform opaque square dots 27 separated by transparent line areas 28, the ratio of the line spare area to the dot area generally being about 3 to 1. A positive of the subject (for example the tone scale of Figure 1) is then printed on the screen exposed resist, the exposed resist is then transferred to the cylinder or form and developed and the cylinder is then etched in Well known manner.

As illustrated in Figures 3 and 4 the usual photogravure etching or printing form 29 formed in this way includes a series of ink receiving pockets or wells 30, 3|, 32 and 33 having substantially square surface openings separated by thin substantially uniform walls of metal, usually copper, which in monotone printing are generally at an angle of 45 degrees to the wiping edge of the press doctor blade (not shown) which in turn is parallel to the axis of rotation of the etched cylinder in the usual rotogravure press. Wells 38 are the deepest, receive a maximum amount of ink and, print the deep shadow tones of the subject. Wells 3| are of medium depth, receive less ink, and print the medium tones. Wells 32 which are very shallow, print the highlight tones. Wells 33 are barely perceptible and print the absolute highlights.

The acid etches the wells into the copper in substantially U-shaped section, and the openings of the well are squares of substantially equal area surrounded by very thin relatively narrow outer metal wall which tend to wear away relatively rapidly under the friction of the doctor blade. This alters the nature of the prints and may require replacement of etchings in long runs. As is well known, it is very difiicult to make replacement etchings exact reproductions of the original etchings.

Also because of the U-shaped section of the wells the full complement of ink is never drawn from the wells in the printing operations with resultant loss of tone. value differences in wells of slightly differing etched depths. Furthermore the amount of ink withdrawn from such wells in successive prints depends largely on the ink consistency which varies materially in modern high speed inks. Relatively deep etched Wells are therefore necessary to secure reasonably satisfactory prints at commercial printing speeds, and relatively full tone print values of the subject are secured only in comparatively slow sheet feed presses with such etchings. As the speed of rotogravure printing is increased with such etchings, the action of impression roll at high speed plus the tendency of the doctor blade to draw ink from the wells result in decreasing quantities of ink drawn from the wells by the web and rapid deterioration of the prints.

In the dot size etching a form 34 shown in Figures and 6 the sensitized resist is subject to a single exposure from a. screen positive on which an image of the subject is formed by dots of varying size. An etching 34 formed by use of such a positive and resist has wells 35, 36, 31 and 38, which are of undercut U-shaped in section as shown in Figure 5 due to the forced nature of the etching. In this form of etching as shown in Figure 5, the well openings are substantially square except where the tonal Values change in a given cell as illustrated at 35a, and are in checkerboard formation, with their sides at approximately forty-five degrees to the edge of the doctor blade. These wells decrease in area from the shadow tone area of wells 35 through the medium tone area of wells 36 to the highlight tone areas of wells 31, with very small wells 38 or no wells at all in the absolute highlight areas. While the variation in dot sizes and the half tone checkerboard or short scale screen arrangement provides greater metal areas between the printing wells for the support of the doctor blade, resulting in more durable printing surfaces than are provided in the usual rotogravure etchings of Figures 1 and 2, the short scale screen formation used and the undercut well formation prevents satisfactory printing in modern high speed presses, due to excessive loss of tone values and the tendency to reproduce the checkerboard pattern in the middle and light tones of the prints as the printing speeds are increased above the speeds of sheet feed presses.

In preparing the dot-size dot-depth etching 39 of Figures 7 and 8, a dot-size screen positive is first printed on the sensitized carbon tissue as in the dot-size process. A continuous tone positive retouched to give varying depth from any given size dot of the screen positive is then printed over the dot-size image to increase the tonal differences in the individual dots. The exposed carbon tissue is then transferred to the printing form, developed and etched into the printing surface. In such an etching, the wells 40, 4|, 42, and 43 decrease in area as in the dot-size etching of Figures 5 and 6, from the deep shadow tones 40 through the medium tones 4|, the highlight tones 42 and the absolute highlights 43. It will be noted that the depths of the wells differ with the areas of the wells, and that in each tone two well depths have been illustrated. The shallower of the wells in each tone illustrates the holdback effect of the continuous tone positive in producing the etching, and the deeper illustrates the well formations when produced without use of a continuous tone positive in the etching operation. The final plate embodying dots varying in size and depth is shown in Figure 7A. The wells in each case are substantially U-shaped and vary in depth in accordance with the tonal values, as shown in Figure 7, the deep shadow tone wells 40 being the deepest. The well depths decrease progressively from the corrected and uncorrected deep shadow tone wells through the medium tone wells 4 I, the highlight tone area of wells 42, to a minimum depth in wells 43 of the absolute highlight tones. face area for support of the doctor blade increases their life over that of the usual rotogravure etchings, and provide about 25% more tone scale than the dot-size etchings due to the depth variations of the wells, the prints fall short of the tone scale attained in the usual rotogravure process, and are useful only for high speed medium grade color work.

My improved printing form 44 (Figures 9 and 10) of the present invention is etched from a novel screen positive of the subject carrying the tone values of the regular rotogravure positive and made as hereinafter more fully set forth. The image on my improved screen positive is formed of substantially square dots of varying size and as more fully hereinafter set forth each dot increases in density or resistance to the transmission of light from its periphery to a central core for motion of maximum density, and each dot from the deepest shadow dot to the smallest highlight dot diminishes in tone value as it diminishes in size. The phrase motion of maximum density has been coined by me to describe the novel growth of the dots and etched cavities or wells in the practice of my invention. The dots are formed by successive exposures causing them to form with varying density, and the etched cavities or wells grow from a pin point core and increase in area as they increase in depth, producing density in printing value. My screen positive is printed on a carbon or pigment resist which is transferred to the printing form, then developed and etched in usual manner. The resulting etching illustrated in Figures 9 and 10, as in the dot-size etchings decrease in area from a maximum in the shadow single tone wells 45 through the shadow two tone wells 45a, the medium tones wells 45 the highlight tone wells 41, to a minimum in the absolute highlight wells 48. In exceptional cases where absolute whites are desired in the high-light tones, absolute high-light tonal values which will produce no dots are created in the negative used as a transparency to produce the positive. In some instances this is procured by the nature of the ground of the copy, and in others it is secured by correction of the negative, all in manner well known to those skilled in the art. The crosssectional shape of each of the wells 45 through 48 is furthermore substantially tapering V- shaped from a maximum at the surface openings of the wells to a minimum at the bottoms. This results in inclined supporting sides for the surface sections adjacent the wells providing improved resistance to the 'doctor blade pressures and frictional wear. The inclination of the well walls of my improved etchings is such that all of the ink is readily drawn from each well for each print under modern high speed printing conditions with normal ink variations. As a result each different size of well, no matter how minute the differences in size, deposits a differ ing individual amount of ink on the print. Each dot from the deepest shadow dot to the smallest absolute highlight dot therefore deposits a distinctive individual tone of dot, providing tone variations not heretofore obtainable in any prior type of photogravure etching when used for high speed printing.

In producing my improved screen positive I may use a camera of the usual half-tone type. I prefer however to use a camera of the type While the larger sur- 54 preferably a diffusing plate.

of the negative is interposed between plate 54 and optical prism '6 which mounted above and in the path of the light projected through the negative. Prism 56, is provided with an exposure shutter 51 operated by rod 51a from the back of the camera in well known manner, and is supported on the end of lens barrel 58. ported in lens barrel 58 is lens 59. The outer end of the lens barrel and the upper part of light shield 55 are supported by a member 60 from the camera body El. Mounted in barrel 58 is a rotatable stop frame 52, and the barrel is secured at its inner end to and extends slightly into a camera body 6!, which at its rear carries a plate or film holding camera back 63.

Mounted rotatably in body BI is a truncated conical tube 64 the forward wall of which is; journalled on the inner end of. lens barrel 58,

adjacent its ends tube 64 is rotatably supported in cradles 55. Mounted on the rear end of tube 64 is a screen supporting frame 66. Tube 64 is connected by an extension 61 passing through a suitable slot in the front wall of body 6| to the stop carrying frame 52. By this construction the screen assembly and stop are held in predetermined longitudinal relationship with respect to each other, the lens assembly and the.

3 for the passage of light mounted in stop;

frame 62 a checkerboard screen pattern of separated dots of the type that will produce the dot formation of Figures 6 and 8 is projected on the sensitive surface. These dots decrease in size from a maximum in the deepest shadow;

tones to a minimum or no dots at all in the absolute high light areas. I However, by use of a series of different stops, such for example of the shapes illustrated in Figures l3, l4 and 15 inserted in stop frame 62 in successive exp0-' sures, I modify the checkerboard screen formation into a full scale screen formation of the inafter described.

For best results I prefer to use a normal or' continuous tone rather soft emulsion plate or film, which cannot be used for the usual half tone screen work, because they will not provide a sharp clot formation of the half tone process plates, due .to their softness. Such normal or soft emulsion plates are used in my improved process because very little light will cause reaction on the plate and create an image. On the other hand, the prior dot-size processes require a very contrasty plate which emphasizes the dot image with respect to the clear plate areas, and require a full complement of light during exposure.

I preferably interpose between objective screen I H and the sensitized plate or film 14 mounted in back 53, preferably held in place by suction,

10 a secondary screen 15 (Figures 11 and 17) disposed directly against the sensitized surface, with its screen lines and transparent or light transmitting square openings respectively in register or optical alignment with the lines and openings of the primary or objective screen 'il so that a single screen image is projected on the sensitized surface. By way of example, with a 150 line 60 to 40 ratio objective or primary screen H as above described I have used a 150 line to 20 ratio of openings to rulings in the secondary screen 15. As will be understood by those skilled in the art the relative screen rulings and spacings may be varied widely depending upon the lenses and camera extension used and the screen positive effects desired. The secondary screen 15, when used, prevents dispersed or deflected light from striking screen line areas projected on the sensitized surface. This deflected or dispersed light results in a light fog in the line areas on a screen positive made with primary screen H only, unless unusual skill is exercised in printing the screen positive on the carbon resist.

To assure proper optical relationship or register of the objective or primary and secondary screens H and 75, the two screens are preferably permanently fastened together after the rulings, spacing, and proper optical relationship have been established for a given camera. This may be accomplished for example by ruling the primary and secondary screens in register on opposite sides of a glass plate of proper thickness, or by utilizing separate screens that are brought into register and properly spaced in a holding frame and then looked permanently in place, or by setting the screens in register and properly spaced in a suitable transparent plastic.

In addition to the usual types of half tone ruled glass screens, I contemplate the use of metallic screens which may be formed with proper opening and line ratios for example by electro-deposition of nickel on master plates of the character described in United States Patent No. 2,024,086 having the desired screen patterns. Such metallic screens have the advantage that they reduce light diffraction to a minimum.

A full tone negative of the subject placed on plate 54 (Figure 11) will be properly focused on the sensitized plate or film 14, and the screen or screens in place in frame 63, the first short exposure is made with the stop 16 of Figure 13 in frame 6!. Stop 16 is provided with a substantially square central opening 11 and is positioned in frame '62 so that the sides of opening 1'! are parallel to the sides of the screen squares. Extending diagonally from the corners of opening 11 are rectangular openings 18 which preferably extend to the full capacity of the lens assembly, and are proportioned and arranged with respect to the screen openings so that the light transmitted therethrough increases the light passing through the corner areas of the screen squares to the sensitized surface. With a soft tone com mercial plate, by way of example-with a girls head and tone wedge as the subject, I have made this exposure about six seconds. The dot formation as a result of such an exposure above, when developed, has the general appearance of the formation illustrated in enlarged form in Figure 19, having a square full scale screen outlined with the density of exposure increasing from the periphery to the center of the dot.

After the first exposure stop 16 isreplaced with Y a second stop 19; and given'a second short exposure. This stop preferably is provided with a four pointed opening 80, provided with four pointed arms 8| which extend diagonally a distance from the center of the opening equal to the distance of the outer edges of extensions 18 from the center of the opening ll of stop 16. The maximum diagonal dimension of the openings in these two stops are made equal, and the points-of openings 8| are positioned in frame 52 so they-will coincide with the position assumed by the centers of extensions 18 of stop 16 during the first exposure. This places the diagonal axes of points 8| across the corners of the screen squares, and the stop size is such that there will be no need to make any change in screen distance for the second exposure.

The second exposure is then adding its effects to the first exposure. In the second exposure, which, in the specific example given in connection with the first exposure, was l'seconds, the

erally of the form illustrated in enlarged form in Figure 21.

After the second exposure has been completed a third exposure is preferably made to increase the extent of exposure of thecentral core areas of the dots preferably with stop 82 such as illustrated in Figure 15, which is provided with a small central pin-hold opening 83. In this exposure, which in the specific example given in connection with stops l6 and 19 was about 90 seconds, the central core exposure of the previously formed dot exposures'isintensified further. The third exposure pattern when made with stop 82 alone and developed, is of the general form illustrated in enlarged form in Figure 20.

After the foregoing exposures are completed theplate 'or film is developed, and the resulting screen positive of the subject will be made up of dots of varyingsizes, densities and tonal values depending upon the tonal values of the subject as illustrated in enlarged form in Figures 9 and 10. The tonal values extend over the tonal range of regular rotogravure positive, and each dot has thegeneral pattern illustrated in enlarged form in Figure 18.

Because of its nature, no corrections can be made in my improved screen positive. All corrections must be made in the negatives. However, by the provision of my improved camera in which the proper lens, stop, screen and plate or film relationships and optical registry are all built into each camera for the production of a particular size and type of negative, without any provision for adjustment of anykind except the angular relation of dot position to the negative image, standardized procedures and formulae informulae and procedures which result in uniformly highgrade etching high grade prints with minimum skill in production.

In etching with my improved screen positive the image is printed on the sensitized 'resist by asingle'exposure and the resist is then transferred to the plate'or cylinder-and the usual rotogravure etching procedure is followed. The etching .period usingmy improved screen positive is about from twenty-three to twenty-five minutes giving control of the etching approximately equal to that secured in the regular rotogravure etching. The

resulting etching consists of varying size and tone wells having V-shaped cross-sections 45, 46, 41

and 48 such for example as are illustrated in fore intended to be embraced therein.

What is claimedand desired to be secured by United States LettersPatent is:

.1. The method of forming a screen positive from a sensitized soft emulsion surface adapted for etching an intaglio printing form embodying wells of V-shaped section which comprises the steps of making a continuous tone negative of the subject; placing a first screen at approximately half-tone distance from said surface; placing a second screen in contact with said surface in optical register with said first screen, said second screen having the same linage as said first screen but having a smaller ratio of opaque to transparent areas; subjecting said surface to a plurality of successive exposures with a light image from said negative through said screens and through a series of different stops, three of said stops having, respectively, a substantially rectangular opening having extended corners, a substantially cross-shaped opening and a relatively small circular opening, said openings being oriented with respect to said screens to form the outlines, accentuate the corners, and form central cores in separated square distinct exposed dot like areas in gravure arrangement on said surface, with each dot having a central core of maximum exposure and gradually decreasing exposure from said core to its periphery; and developing the thus exposed surface to produce thereon a positive image of thesubject made up of transparent areas and distinct separated dots of varying density.

2. As an article of manufacture, a screen positive produced in accordance with the method of claim 1.

3. A method of forming a screen positive adapted for etching an inta-glio printing form embodying wells of V-shaped section which comprises the steps of subjecting a sensitized soft emulsion surface to a plurality of successive exposures of a continuous tone negative, each exposure being made through both a primary screen at approximately half-tone distance from said surface and through a secondary screen in contact with said surface and in optical register with said primary screen, said secondary screen having the same linage as said primary screen but having a smaller ratio of opaque to transparent areas; each exposure being made through a different stop, three of said stops having, respectively, a substantially rectangular opening having extended corners, a substantially cross-shaped opening and a relatively small central opening, said openings being oriented with respect to said screen to form the outlines, accentuate the diagonals and corners,- and form central cores in separated square distinct exposed dot like areas in gravure arrangement on said surface, with each dot having a central core of maximum exposure and gradually decreasing exposure from said core to its periphery; and developing the thus exposed surface to produce thereon a positive image of the subject made up of transparent areas and distinct separate dots of varying density.

4. As an article of manufacture, a screen positive produced in accordance with the method of claim 3.

LUCIEN C. AUSTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,452,077 Huebner Apr. 17, 1923 1,562,757 Hammond Nov. 24, 1925 1,773,887 Stirling Aug. 26, 1930 1,849,036 Ernst Mar. 8, 1932 1,909,939 Ernst May 23, 1933 1,991,888 Ernst Feb. 19, 1935 14 Number Name Date 2,010,042 Stirling Aug. 6, 1935 2,024,086 Ballard Dec. 10, 1935 2,039,195 Stirling Apr. 28, 1936 2,040,247 Dultgen May 12, 1936 2,048,876 Marx July 28, 1936 2,148,519 Wilkinson Feb. 28, 1939 2,226,086 Wilkinson Dec. 24, 1940 2,282,337 Mics et a1 May 12, 1942 2,376,596 Huggins May 22, 1945 2,387,048 Alger Oct. 16, 1945 2,446,193 Rice Aug. 3, 1948 2,480,400 Dultgen Aug. 1949 FOREIGN PATENTS Number Country Date 686,763 France Apr. 15. 1930 711,572 Germany Feb. 11, 1943 OTHER REFERENCES Smith, Other Uses of Half-Tone. British Journal of Photography, March 22, 1940, pages and 136 cited.

Mertle, Half-Tone Stops, American Photoengraver, September 1929, pages 937 to 951, pages 938 and 942 cited.

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