US2482638A - Photogravure - Google Patents

Description

ggg. R. SCHUL-rz ET Al.

sept. 2o, 1949 PHOTOGRAVUIRE 2 Sheets-Sheet 2 Filed April 12; 19,45'.

DE@ m' ffy/WWW@ //Ji///7/y I INVENTORS Oswmn R. ScHuLrz Rosam- F. Ne sn.:

if y@ Patented Sept. 20, 1949 1 UNITED STATES PATENT 4OFFICE PnoToGaAvURE Oswald R. Schultz, New York, N. Y., and Robert vF. Nestle, Ardmore, and Matthew J. Romano, Philadelphia, Pa., assignors, by mesne assignments, to Triangle Publications, Inc., Philadelphia, Pa., a corporation of Delaware Application April 12, 1943, Serial No. 482,712 14 claims. (C1. sat-5) .l e This invention relates to photogravure. It is an object of the invention to produce an improved transparency for use in preparing gravure printing surfaces.

It is a further object of the invention to provide an optical arrangement and method of exposure by means of which such improved transparency is produced. Y

A still further object of the invention is to provide a method of making intaglio printing surfaces which produces an improved printing surface without increasing the number of steps or quantities of materials beyond those which are necessary in conventional photogravure. A

With these general objects and still others which will appear in the following full description in mind, the invention consists in the methods and articles of manufacture which will now rst be fully described in connection with the accompanying drawing and then pointed out more particularly inthe appended claims.

In the drawing: Y

Figure 1 is a theoretical schematic plan view of a portion vof Ya conventional intaglio printing surface;

Figures 2 and 3 are sections, respectively, lon the lines 2 2 and 3-3 of Figure 1; y

Figure 4 is a theoretical schematic plan view of a portion of a reverse half-tone intaglio printing surface;

Figures 5 and 6 are sections, respectively, on the lines 5-5 and 6 6 of Figure 4;

Figures 7 and 8 are sections similar to Figures 5 and 6, respectively, but illustrating a modied form of reverse half-tone printing surface;

Figure 9 is a theoretical schematic plan view of an improved intaglio printing surface;

Figures 10 and 11 are sections, respectively, on the lines I-Hland IIJ-II of Figure 9;

Figure 12 is a schematic view of a camera arrangement suitable for practicing the method of the present invention;

Figure 13 is a schematic view of a portion of a screen suitable forv use in practicing the method ci the invention; l

Figures 14 and 15 are views showing aperture disks or stops suitable for use in practicing the I method of the invention; and

' density Vmaybe produced by conventional photogravure, by reverse half-tone and by the method "of the present invention. In each case a pattern 'of Atwenty-five cells isl shown and the 'individual `cells may conveniently be'identied by considering Ythe columns, starting from the left of the figfure, as successively lettered a,.b, c, d, and e, and the rows, starting Yfrom thetop of the gure, as A,`B, C, D and E, so that, for example, the center cell in each figure will be identified by the symbol Cc, and othermcells correspondingly. In the conventional gravure printing surface, the variation in tone is achieved primarily by f varying the depth of the ink cells, thus, as indi- Y cated in Figure v2, progressively lighter tones may be produced by employing in the various areas of a picture to be printed progressively shallower inkcells Aa, Ab, Ac, Ad, and Ae. To illustrate the characteristics of the surface for printing a iull Vtone the four upper left cells Aa, Ab, Ba and Bb are all shown as full depth.

From the standpoint of tone reproduction, the conventional gravure printing surface has a very marked advantage in that tone variation may be obtained by varying the thickness of the inklaid upon the paper, instead of merely varying the area of the inked surface, as in half-tone printing. 'Furthen in the deep tones, most of the surface may carry ink so that it is possible for the ink to iiow on the paper so as to produce a solid color, in which the areas in contact with the walls between cells have been covered with ink,

as well as those whichV have come in contact with `Athe ink carrying cells. The proportion of the ink carrying cell area tothe total area may be large. For example, the width of the cells (Fig- :Dure 2) may be four or five times as great as the width of the cell wall between cells, so that about siXty-ve or seventy per carries ink. Y

Conventional gravure printing is, however, subject to a distinct disadvantage in the printing of Y,light tones due to the fact that in those tones cent of the surface area *the cells e.=-g. Ee of-l Figures 1 and 3 must be made so shallow that diiculty, due to action of the doctor and due to drying, may be encountered.

As will be understood by those skilled in the art,

the Aconventional gravure printing surface is a polished skin or shell of copperV deposited on a cylinder and being only about six one thousandths of an inch thick. A typical cell'formation may @comprise about lines to the inch, or 22,500 cells to the square inch. In view of these considerations, the maximum permissible depth of fetch in the deep tones is limited, and accordingly the depth of etch'rrequired to produce sufficiently light tones in the highlights may be impractically slight. This defect manifests itself in a number of ways: First, since the highlight cell is very shallow it is possible for drying of the ink to affect the printing very materially and in some cases to obliterate it.; secondly, .the `c ell wall being relatively narrow, a c ertain amount of wear due to abrasion by the doctor will occur and in the case of a very shallow cell the relative decrease in dep-th thus produced may be such as seriously to affect the printing; thirdly, the effects o'f variation in the viscosity or other .characteristics of the ink and the doctor blade actionmaiybe found to interfere with the quality `o. prin.ting .produced by such an extremely shallowrcell.. .it .is-a primary object of the present invention to produce `an intaglio printing surface which retains the advantages of conventional gravure in the deep tones but remedies the defects of conventional gravure in the light torres.

.The conventional photogravure ,process .is well understood. Briefly it .involves Vthe following steps: First, .a negative -of the lcopy to ybe reproduced is made.; second, this .negative .is photographed Without using .a ,screen so .as to produce a .positive transparency.; .'third, .a .sensitized resist, .typically .carbon tissue, is .exposed .through a gravure screen; fth, the .resist is transferred to the .copper cylinder .and .developed to dissolve away the 4unexposed .areas-.according .to the extent .of exposure, .those areas which have been subjected to thegreatest exposure being rendered more insoluble and those which .have Abeensubjectedto the least-.exposure remaining relatively soluble; .and sixth, the printingsurface is .etched through the .resist ina bath which .consists 'typically of a .series of `progressively -weaker `solutions of ferrie chloride. The screen employed, will, -of course, be composedof'opaque .areas `corresponding to the ink cells sto lbe produced and of transparent lines, .forming :a .transparent ,ground which corresponds Ato .the Ycell .Walls .or unetched .surface.

This process .may .bemodied lin various ways, to obtainspecial results where fdesired. For example, rthe .order .of Ithe .exposures of the carbon tissue to the screen .and to the positive transparency may .be .in-vented. Also, .the transparency itself .may be screened, and in this ,case the .screen employed will yloe a :negative `intaglio `screen having relatively transparent areas .corresponding to the ink cells to .be ,produced `and relatively opaque areas-or .ground corresponding `to `the unetched surfaceor cell Walls.

The conventionahgravure process, .however performed, has ver-y vdesirablecharacteristics of simplicity -in the .number -of ...steps frequired, economy in materials used, avoidance yof .registration .diiculties and ease of retouching. With .regard to the last-feature, rretouching maynormally :be ldone .on .the positive, lbutmayalso be .done-on the negative. It is an 'objectief the present inventionto produce a printing surfaceof ,the character indicated above, without fsacuicing the `major advantages of -the conventional :photogravure process.

The invention .will be more clearly Aunderstood by alsorecalling,briefly'someof the characteristics of reverse .half-tone ,printing This .process is substantially as old .as photogravure itself, and

involves the productionof a printingsurface simulating `a .half-.tone surface, but carrying the ink -in `depressed areas instead :of aupon raised areas. Such .a surface, having tone variation `similar .to that of Figures .1, 2 land A3 :shown -in VFigures 4 4, 5 and 6. The largest ink carrying cells being of the same area as those in Figure 1, and an equal minimum thickness of wall between cells being preserved, it will be observed that a much larger area of the printing surface is required .to `carry the .same quantityof ink. .For example, where :a conventional :gravure surface may comprise ink cells occupying about seventy per cent of the total surface in the deep tones, reverse half-tone can have ink cells occupying only about forty iper cent of the total surface, which means that V.the gravure surface is inherently capable of :laying seventy-'five per cent more ink on the k,paper inthe .deep tones than can be done by :reverse Vhalf-tone. Figures 5 and 6 illustrate the cell `,formation :of a reverse half-tone surface theoretically, `all cells being of equal depth. It is, `however, apparent that all cells will not be `of equal depth as those of larger area will be necessarily of greaterfdepth, due to the action of the etching bath. This .effect `is .noticed Yeven in relief half-tone .butis immaterial .in Athatcon- `nection for the reason -.that .theraisedareas 4rather than the depressed areas dothe-pr-inting. Figures 7 land 8 .may be `.taken `.to illustrate .either this effect or theelfect -of .known processes by which explicit :provision -is.rnade for vary-.ing the depth of etch as well as the area -of .the inkcells. Such .proposals are all subject to .the-common ldifficulty that vweh-ile an improvement in reproduction may be obtained in the :lig-ht tones, 4this is vdone at the expense yof the .deeptones and the characteristic gravure effectis rlost. `Also, it is not possible, as a practical matter, to control -the A.depth of etch as rindicated in Figures 7 :and 8 `Without employing a plurality fof transparencies or Vnegatives which require :to :be superposed in accurate registry. For such reasons, -the -characteristic simplicity and econoxnyfinmaterials of conven- .tional photogravure are lost, lin large measure, and the plurality-of Vnegatives yor l,positives which are necessary introduce difliculties :in retouching.

According .tothe present `invention -a printing surface is produced which has the conventional gravure formation .in the :deep tones. As indicated in Figures :9, `IL0 Vand l1 :the Vdeepest tone `formation of Athe printing-.elements (cells Aa, Ab, Ba, Bb) magy be identica-l with that of a conventional gravure printing surface (Figures '1, 2 vand 8). VIl-Iowever, in the lighter tones the relative widths of the ink Cells :and the cell walls are changed so that the ,cells `become progressively smaller and the walls 'progressively wider. In this way, fthe .amount 'of ink carried in `the lightest areas may .be reduced :to ,anydesired extent without requiring :an impractical'ly shallow ink cell`. -Forfexarnple `if the cell Ee `Aof Figure 9 be considered :as having Va width which Yis one eighth that-of `the cell Aa 4of ,Figurefil (or the cell Ee of Figure 1*),it will 'have 4only onesixty :fourth `the area and may be made sixty-four .times as deep asithe cell Ff of Figure 1, i'f Lit is to carry the same vamountof in'k. IAS -willlbe immediately apparent to those skilled in the art, a printing surface such as that of'Figure 9 possesses all the advantages of aconventional gravure surface in the deep tones while remedying its defects in the light tones. .This .is due to `the'retention in the deep tones of the characteristic continuous `cellularstructure of the ,gravure printingsurface .as opposed to the checkerboardstructure `of a reverse half-tone.

The method by Which .the surface of Figure 9 maybe `produced may be best described 4with refsometimes as llow-'as 0g5; as-compared with contrasts in excessof 1.0-'Which are customarily employed in known processes;. This inV itself indicates the desirable 'characteristics' ofthe method of the invention, as it" may be :practiced so'asl not to lose contrast either at fthe upper or` lower end of the density vscale.1..l The second step involves exposure'of the. negative I in a conventional copyingcamera such as isY now used in conventionalv process'wo'rk.. The 'i lensof the camera is indicated diagrammatically at 2, the'iris diaphragm orother aperture'disk at 3, and the positive plate at 4.` `This'plate 4 may be either aA plate of one of the commercial contrasts used in'conventiona-l photogravure or may be of greater or less contrastfas forexample a line 'or process plate, the control afforded by the processbeing suicie'nt to permit use of widelyvaryingemulsions and development procedures. A screen `5 is employed in exposing the positive 4 andwill, in effect, be the negative of a conventional gravure screen, having transparent areascorresponding to the ink cells to be produced and opaque areas corresponding to the cell Wallsto be produced. A cross-line screen may be'employed, as usual, so as to produce square ink cells or printing elementsi By utilizing suitable optical arrangements, a positive suitable for producinga printing surface having the characteristics ofv that of Figure@ may beobtained. The ratio between the opaque lines of the screen andthe transparent areas between lines necessarily depends upon'or, conversely, if a given screen `is to be used, influencesfthe spacing of the screen from the positive emulsion and the character and-size of apertures used. Considerable variation in the ratio is therefore permissible, but a screen in which the opaque lines are equal in Width ortwenty per cent greater in width than the spaces between lines will be found" generally satisfactory.. Figure' 13 illustrates a portion of such a screen,v on-an enlarged scale (about fifteen diameters); the -.1ine Vof the screen beingY indicated .by the referenceinumber 1. Specic conditions, where'r'efe'rred to for they purpose of illustrating the'process more clearly, will be based on :the assumption that va .screen of such ratio is employed. "In away which will now be more fully described, opticalV arrangements are utilized by means 'ofWhich the effective area' of the light spot produced uponthe emulsion'by a given transparent screen elementmay be either larger, equal to, or smaller than the area ofthe transparent screen element itself; Moreover, these optical arrangements permit orientatingv the various light spotssimilarly to the transparent screen elements so as toproduce a truev gravure cell arrangement. The positive 4 is subjected-to two exposures,

one through an aperture board B (Figure 14) 'haV- ing peripheral apertures, preferably rectangular in shape as shown 'and symmetrically arranged about the lens axis-I0, and the other Athrough an aperture board'l I 4(Figurel) having acentral aperture I2 concentric'withthe lens axis I0. Re-

ferring again to the assumed'illustrative condition, a 150 linefscreen will beplaced' about 1% inch from the positive emunion, making thesistance of the rulings therefrom'about 1/8 inch, and an exposure of aboutl to 30 seconds may-be 'I given through the stop 8 `and about 5 minutes through the stop I I. The stop 8 will be placed in the camera so that a diagonal I3, of the square in which the openings 9 are arranged will be in alinement with the line .'I, of the screen.

' The exposure through aperture 8 will produce light elements corresponding to the transparent elements of the screen having much the appearance of Figure 16, the four apertures 9 projecting rectangular images arranged in a cross and the effective area of these images varying in accordance with the transparency of the negative. As will be understood by those skilled in the art, each rectangular image will be brightest near its center and will shade off toward its edges, ultimately shading 01T to a point where there is insuicient light to have any operative effect on the positive emulsion such as will carry through the subsequent processes of exposure of the resist, development of the resist and etching, so as to be apparent in the printing surface. In view of this, the light elements projected on the positive emulsion will have progressively smaller effective diameters asthe density of the portions of the negative to which they are exposed increases. In this Way, negative areas of progressively increasing density may be made to produce exposure patterns on the positive emulsions having progressively decreasing diameters, and corresponding in order, for example, to the-ink cells of different depths which it is desired to produce in the top row of the printing surface shown schematically in Figures 9 and 10. As -will be noted, the four brightest points :c of the images produced remain in the same position, from picture element to picture element, while their intensities and effective diameters change. By exposure through stop I I, a pattern of light elements having effective areas such as shown in Figure 17 may be produced, and these elements will automatically be in register with those of Figure 16, as the lens, the negative, the positive and the screen all remain inthe same position for this exposure. These elements will, of course, be brightest at their centersy and will shade olf toward the edges. f

The superposed light elements of Figures 16 and 17 produce composite elements as indicated in Figure 18. Each composite element contains five bright spotsarranged approximately as indicated, contributing to the uniformity indensity of the dark element produced when the .positive than toward the corners. A

plate is developed.'

As will be understood, the usual phenomena of spreading of light both by the lapertures and screen and in thephotographieemulsion itself, will occur, and will Alargelyobliterate-thesharpness O f the outlines of the composite elements, so that the Ydeveloped positive will be formed of printing elements, or relatively dense elements, which are Ysubstantially square and present the appearanceand arrangement of the ink cells of Figure 9, and which are interspersed on a transparent ground having the form of the cell wall structure of theprinting surface of Figure 9; yBy suitably relating the two exposures, the composite elements may also be `:made to assume the form of a four-sided cuspidalV gure, or square with concave sides. This eiectgmay be employed-to insure the production ofa truly square ink cell, by counteracting the tendency ofthe etching bath to eat away the cell wall4 faster toward its center The stops, 8 and III may be simply inserted successively in the lens'barrel, in the slot frelquently provided :adj acentian iris "diaphragm for l'thatpurpose, or-successive exposuresthrough the stops provided for inrany other Vconvenient manner. The =order ofthe two exposures is not critical. Forexamp'l'e, a-'stopahaving'both perpheral apertures 9 anda central aperture l2 may be'used, part of the exposure being given through all apertures Vand Ethe remainder through .only Vthe lcentral aperture, the peripheral apertures being covered. Theoretically, by exactly proportioning the peripheral apertures and the central aperture, a single exposure through all apertures might be given to produce the desired eiiect. This, however, would present no advantage Vand `would interfere `with obtaining the very desirable lcontrol which can be obtained in practicing Athe present method as more Vfully gone into below. 'ItshOuld be noted at this point, however, that; Where the 'lens'used'is provided with an iris diaphragm, the iris diaphragm itself may be used as the aperture 112, it being unnecessary to insert a separate stop I i.

4The result of the foregoing procedure is to produce a screened positive transparency in vwhich vthevarious:printing elements are arranged in a gravure pattern, butin which the transpar- "ent groundvforms a rectangular network of lines of varying Width, vandthe printing elements occupying the 'interstices in this network are of progressively less density as their width decreases.

Inasmuch as a screened positive transparency Yis-produced, the step of exposing the carbon tissue through a separate screen may be eliminated from 'thevconventional gravure process and the carbon tissue is exposed merely through the positive transparency. 'The optical arrangement of the invention makes it possible to obtain the required areas and depths of cells in the printing surface While maintaining a proper Cell Wall structure.

The remaining steps of developing the carbon tissue and etchingthe cylinder are carried out as in conventional photogravure andrequire no iiurther description.

The primary requisite of a positive transparency for use in practicing the method of the invention is that the area of the relatively opaque elements corresponding to the ink cells to be produced on the printing surface be varied so that the-elements corresponding to the lighter areas to be printedwill be smaller and those corresponding tothe darker areas will be larger. This variation in area should follow with reasonable fidelity the tone variation of the picture to be reproduced. In this connection, hovveverfV it should be noted vthat the areas ofthe picture `elements need `not be proportional to the tone density of the picture to be reproduced. In other words, since the ultimate control of tonevariation involves also the depth of etch in the various cells a reasonably wide variation in the contrast range of the positive transparency (considering only the area of the elements and assuming them'all to be of equal density) is permissible and may in many cases be desirable.

The secondary requisite of a positive transparency to be used in practicing the invention is that there be a difference in density between the picture elements of larger area and those ofl lesser area. The exact amount of difference is not critical as the depth of cell produced in the printing surface need 'not and in general will not correspond ,proportionately or Vin any other specie way with the ,photographic density of the "one `varies with the .'other.

corresponding ielement `:of the -transparency.

This is due to the fact that the depth Vof Vetch in .the various tones :is fcontrolled in Lthe etching process vbyivarying the strength ofthe successive baths 'andvthel'engthfnf time to which theprinting surface and resist are subjected to the successive :baths .Due `to `this, .indistinguishable printing Vsurfaces .may be Vprepared .from transparencies `having vWidely diierent contrasts.

Thepossibility-of .controler cell depth or tone contrast in the :etching bath-.which is inherent in the photogravure processfmakes it'possible to pay attentionprimarilyto fthe'area of thezprint- -ing'elements ,produced inthe positive transparency. vThe*variationiinfdensity :or the printing elementswill largely take care of'itself. A gradation in densitysfrom`-the llarger printing elementstoitheismaller oneswilloccur and so long asithisfis suicienttomakeit possible to `control :the fdepthf of etch, Ythe precise :limits of vvariation are .not critical.

The process .of the invention, .as described above, oiers Averygreat possibilities for control.

itionin width of the rink cells as compared with I.the variation in depth.

.The .exactrdimensionsland shapes of the apertures lused :are -not critical, :and vmay be varied without varyingthe :eie'cts achieved, Where the screen or 'screen .distance vare compensatingly varied. Theprinciples controlling the choice of apertures will besbest'understood'by considering :the #effect of .exposure througha single aperture "of known type. 5A great variety of such aperturesis knowninprocess work-generally and it Will suflicetodiscuss lbut two of the possibilities.

:If it beatt'empted to produce-'a positive transparencyV such fas is v:produced by the present imetho'd, `usingsimpl-y yaicentral aperture such as the aperture I2,i.it willbe `found that the eiiective areas of-the exposurefelements and the eective brightness 'areinextricably connected so that the Obviously, density variation of the .negative will tend to be multiplied, manifesting :itself :both in increased area of the printing elements and'in increased density.

.Fromzthe standpoint of the transparency, there- Tore, an 'extremely low 'contrast emulsion and development .process 'will be found necessary.

hm"This,'h'ovvever, '.Willfmake it Aimpossible to obtain `result in ndestroying the cell Wall structure.

a sharply dened transparent ground and will A further diflculty will be encountered due to the fcenter iparts offallelements tending to be exposed so elosetolthellimito'rexposure of the nlm that all cells will-comence to etch at about the same time in thebath. This eiect makes it impossibletofetchfa gravure printing surface proporly, .for,;a's is Welliknown, there must be suieral masses `:of fdeep, middle and light tones to cientdifferenceinthe.resist'thickness of the genpermit'controlrof-which setof tones is etched by using 'different strengths of fetching baths.

VA single-exposure'through the peripheral apertures v9 will.V on ,the other .hand.result in a .positive in which` the printing Velements .spread fandcoa-'f lesce one intov the other before'suicienti density. is achieved. Y :i fv 1.a With .a half-tone- Vscreen formation, .consisting of. a. screen and anv aperture-.related thereto `so. asrto produce a half-tone exposure pattern'a' gravure pattern cannot of course be obtained.- In the second place, the .diniculties just mentioned are aggravated, as the diagonals ofthe printing elements .are in: ralinement andthe-.tendency to' break down the transparent ground is aggravated.: In such formation, vas* is Wellknown, when anunsymmetrical aperture pattern viszused it must be placed at forty-five degrees' tothe screen. lFor example; when anl aperture :ofl known type, and. consisting of a cross-shapedopening is used, an arm of thecross will be at forty-live degrees to the screenline 1 rather thaninalinement with it.

In the present method,g onthe other hand, a true gravure screenk formation is employed, and the diiculties above mentioneddo notoccur.y For example, the aperture: 1 2 may be such that; an extremely small andsh arp exposure'element is. projected on the positive emulsiomand exposure may accordingly be prolonged so astojobtainsufa;

lcient depth in the highlights Without-spreading lap slightly Where the more transparent areas of ;1

the negative are being reproduced. f1 he aper-fture l2 is preferably'ofmsuch diameter as to loewholly inside the innerA edges of the apertures 9 andthe best results willordinarilybe,obtained with a smally stop, such as about jzfl to i190;v

'As will be clear from the foregoing description,

dthe present processfinvolves noadditional steps or materials as compared .with .conventicmal-A photogravure. Thestep, of exposing-,the Vcarbon tissue through a screen is eliminatedk andthe positive giventvvo exposures instead of` cne ,1 ,Re-

touching, while itmu'st be done upon the negative, can conveniently bedone in this "way, and. the complications involved in .retouching where registered transparencies" `'are employed, are...

avoided.

The essential characteristic of the'novel trans-N` parency produced is thatV it is'compose'd ,ofd picture elements the denser of Whiclifa'e arranged inw-a gravure pattern While thelesddense elements grow progressively smallerjThe pictureaccord-U- ingly will be represented by areas composed.of a gravure pattern Kof picture elements, the deepv tones having relatively wide'a'nd dense picture f elements and narrow transparent'A ground lines and the lighter areas havingrelatively narrow. and less dense elements separated by wider transparent ground linesf As is apparent, the optical'f arrangement'discu'ssed mayl be used to produce a n pattern in which in the light tones the picture elements are round, and by using-central apertures i of dilerent shapes, picture elements of different shape may be producedinthe lighter `tones wit-h'- f out disturbing the deep; tone: gravure formation. Y

Such procedure, while possessing-n0 advantage, may be followed without departingfrom the in-A vention. vIn particular, the transparency havingf" the gravure pattern ofFigure `9 in the `deep tones,

and a half-tone -patterndikethatof Figure 4 in...

picture elements. theyiwill be arranged in a honeycomb or "continuous cellular "pattern in the deep tones, in 'which :thefpolygonal or other shaped. elements are 'arranged-.with their sidesV rather 'than their-vertices adjacent.' f

The present process permits of vreproducing ma teria] which combineslpictorial and type or line subject matter by incorporating all the'material in the original. negative andaprintingsurface Vcapable of: producing sharp andsolid'type andline Work andalso capable ofproducing delicate gradation. evenin the highlights is readily obtained. Furthermore, the processis adapted to producing satisfactory monotone, and two-color AThe essentialcharacteristic of the. method of. the invention isthat aA true gravure screen arrangement is employed ,for the deep tones. this arrangement, anA exposure isgiven through the peripheral apertures .with the diagonals, or

greatest diametersv ofthe aperturepattern, in line withv the screen, as it is only vin vthis Way that a ture gravure pattern may ber obtained While caus the centers of the picture Velements isthen given,y

and thev specific shape ofthe picture elements produced by this exposurel alone is largely immaterial as it is sufcient-localized or concentrated as not to obliterate or disturb thegravure pattern of the deepftones,-whi1e the specic pattern produced in the lighter tones is not vital.

In color printinga plurality'of separation negatives areeemployed as usual, a positive transparency being made from-each. As the procedure followed is Well known, `it is unnecessary to describe it in detail, .beyondcommenting briefly on certain points. "As is apparent, Asorne or all of the different transparencies or printingr surfaces used for producing the color picture may be preparedaccording to the. present invention and others according to the conventionalphotogravure method. Screenangles will be varied as in. conventionalY gravure, it being necessary tov note only that the aperturev boards Will also be VAturned so as to preserve the proper relation to, theV screen. Additional possibilities of ,control are opened up, however, asthe light tone pattern` maybe different in the transparenciesV for' thev diierent colors. Also, as will be apparent to 4those skilledin the art, the .double contrast control afforded bythe present invention may readi- 1y be employedto obtain accurate rendition of very delicate intermediate' tints and shades yof tints without disturbing` the .stronger colors. and light tints and shades oftints.

What is claiineclis:V e Y 1. ns a new article,l of` manufacture, a picture l transparency comprising a substantially uni-`v form groundandpieture "elements of varying 2' densities, the picture elements which have densities diieri'ngmost from said ground being arranged in a gravure screen pattern and the picture elements Vwhich yhave densities diiering leastfrom said. groundhaving areas decreasingv progressively withA decreasing-density differencefromthe.-` grounds each?. picture.` elementi. beingi' composite and being. defined.. by; acentral spot.

and a piurality of-;.corner'spotsgrouped: thence around',` thev placement andV spacingl of thef spotsbeing` the same; in'u the various-.1e1ements,.andzeacir spot` comprising.v ar-center havinga density di'ier'- ing; most: from1 the: ground. and: differing` progres sivel-y less indensity from thekground asthe dis? tance from; the center increases,` the;I said spots-` of each element.. overlapping sov as: tos formi a. single pictureelement.

2; As a new article-.ofi manufacture; a: picture` transparency;A comprisingra'. substantially uni:- form groundl and` pictureelements; of varying; densities. the'r said'. picture elements being: ar!-` ranged in af. gravure screenz pattern', the; areas'. including, elementsA having densities. which differ'l most from'l saidi grot-indi comprising. relatively large' picture. elements;- separated. by relatively narrow ground?. areas; and'. thef areas.' including'v elements.` having. densities. closer to. that or the grou-ndiv comprising.. progressively smaller' picture elements and'u Wider ground. areas; each.v picture element being composite and being dened by44 a" central spot. andi a; plurality-A of corner spots grouped..therearoundmhe placementand spacing" of'y the.. spots being.. the sameV in.. the various elfements',. and= e'aclLspot` comprising a center have ing a density: differing most-from. the ground and differing. progressivelyless in' densityv from'A thel groundf asA the' distance :from the-center increases, the saidi spots.V of; each element' overlapping so as to, form alsinglepictureelement.

3. Asia:A new articleof` manufacture, aV pictureL transparency' comprising a' substantially` uniform groundl forming a i crosst Iinescreen pat-tern of lines of: varying width and@ defining enclosed" picture elements'oi` varying area; the said pictnre elements having densities progressively further' from: that of the` ground with increasing area', each picturev element being composite andbeing' dei-inedv by' a' central spot and` a'Y plurality`A of co1.- ner spotsA grouped therearound; thel placement and spacing or the spots being the-samel in` the. various elements; andn each spot comprising a' center having a` density diiiering Vmost from' the'v ground and diiering progressively less in' density fronrthe ground as= the vdistance from the' center increasesi the said spotsi ofi each element over'- lapping soaste-form a sngi'e picture element.-

4. Asza new" article of manufacture,l a positive picture transparency comprising a relatively' transparent ground* and picture-elements'of varying densities, the denserv orsaid elements being' arranged? in a' gravure screen pattern and;` the lessdense of saidelements'being' ofprogressively' decreasing area with` decreasingv density', each'v picture element being' compositeV and" being" Yde'- nedf by acentraly spot andt a plurality of corner.v spots grouped" therearound; the placement. and spacing of the spotsbeing the same inthe'vari'- ous elements; andA each spot comprising a' centerof greatest density and decreasing in density as. thedistance from the center increases,V the said spots of each element overlapping so as to form a single picture element. Y

5. As a' new article of" manufacture, a positive picture transparency comprising a relatively transparentground. and picture elements. of varying densities, the said. picture elementsbeing arranged in. a. gravure screen pattern, the areas includingl denser elementsfcomprising rela= tively large picture.- elements separated by rela'- tively narrow' ground areasY andi the areasy ina ofi cornen spots grouped therearound, the" placement and: spacingsof theespotsr'being. the:` same: in the various': elementai` and each` spot'. comprising ai center' of greatest. density andi decreasing inv densityasithe distaneefrom the center increases, the said spotsoteach elementi overlapping so as toioi'nt'a..single.picture'element'r a'- n'ew: articlel of manufacture, a positive picture transparency comprising a relative- 1y: transparent lground-forming afcrossfline screen patterni. of lines.: ofi varying widthY and defining intersticesof'varying area, and.v picture elements the distance from the'centerf increases, the said spots-bf each element' overlappingv so as to form asingle picture elementi '7. The method of4 making a transparency for use in preparing printing surfaces which comprises'l photographing a:v picture tube reproduced through a' screen; part of-" the' exposure of` the said picture# being given through` a stop having a centrall aperturel and part of the exposure of thesaid picture being given through a stop' having peripheral@ apertures; the said peripheralV apertures and screen beingfscrA spaced: and angularly related' as toproducea pattern of exposed elements having` their` greatest' dimensions substantiallyin alignment with the greatest dimensions oi" the transparent elements of the screen.

8; Themethod accordingx to'claim 7", in which a cross line screen' is employed and' thesaid peripheral apertures comprise four: apertures arranged synunetricaily about the lens axis.

9i ThemethodfA according to claim 7, in which the'` said peripherall apertures' are. spaced around the-lens axis outsidel the boundary of said centrai apertures.

102 Themethod'according `to claim 7, in which aY cross line-screenL is' employed and the said peripheral apertures comprise four apertures ar.- ranged'! symmetrically' aboutV the lens` axis and spacedi around" the same; outsidethe boundary of.v saidcentra'laperture;

11. The methodofpreparing printing surfaces.

posure of the. said picture being given through` a stop'having a. central'.aperture andpart of the exposure of' the said picture.. being given through a stop having peripheral'. apertures, the saidperipheral apertures.. and. screen being so spaced andY angularly related aslto produce'- a1 pattern of exposed elements.. having.. their greatest. diameters.V substantially in'- alignment wththe greatest diameters of the transparent. elements of the screen; andv the'. relative .exposures through said central4 aperture and?.` saidl. peripheral apertures beingk such: astoifproduce'f.l a photograph having exposed; elements of varying; densities, the denser ofV said. elements', having a gravure screen formation: and7A the less ydense off saidf elements de-v creasing in` area withl decreasing density,

12. The method according to claim 11, in which a cross line screen is employed and the said peripheral apertures comprise four apertures arranged symmetrically about the lens axls.

13. The method according to claim 11, in which the said peripheral apertures are spaced around the lens axis outside the boundary of said central aperture.

14. The method according to claim 11, in which a cross line screen is employed and the said peripheral apertures comprise four apertures arranged symmetrically about the lens axis and spaced around the same outside the boundary of said central aperture.

OSWALD R. SCHULTZ. ROBERT F. NESTLE. MATTI-IEW J. ROMANO'.

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

UNITED STATES PATENTS Number Name Date 1,773,887 Sterling Aug. 26, 1930 2,010,042l Sterling Aug. 6, 1935 2,024,086 Ballard Dec. 10, 1935 2,040,247 Dultgen May 12, 1936 2,060,640 Shaw Nov. 10, 1936 2,096,794 Dultgen Oct, 26, 1937 2,100,346 Misuraca Nov. 30, 1937 2,182,559 Henderson Dec. 5, 1939 Sept. 1929. Article on Half-Tone Stops, by J. S.

Mertlo, on pages 937 to 948 cited.

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