US2155458A

US2155458A - Method of and apparatus for printing

Info

Publication number: US2155458A
Application number: US36019A
Authority: US
Inventors: William J Wilkinson
Original assignee: Individual
Current assignee: Miehle Printing Press and Manufacturing Co
Priority date: 1935-08-13
Filing date: 1935-08-13
Publication date: 1939-04-25
Anticipated expiration: 1956-04-25
Also published as: GB470385A; BE422922A; FR790457A

Description

Patented Apr. 25,1939

UNITED" STATES .PATENT OFFICE amuse; nm'rnon or up mane-res roa ramrmo t'lonoflllinois No Application August is, 1935,

Serial No. score Claims.

This invention relates to the art of gravure printing and concerns more particularly (a) a unique positive of the subject to be reproduced, used in the making of the printing-plate and its method of production, (b) a novel intaglio print-- lug-plate and its process of manufacture from such positive, (c) a new printirm procedure resulting in ,(d) an improved print presenting the original subject with great fidelity as to all tonal 1n gradations. I

Intaglo printing, as at present ordinarily practised, involves the employment ;of a printingplate made from a continuous-tone positive and a gravure-screen and in which plate the picture is 16 depicted by a series of dots formed as wells or depressions in the'printing surface of the plate,

and the printing from such a plate when inked, the ink being carried in the wells and pressure being applied to force the-ink out of 'such' wells 20 onto the paper or other surface, suchmethod being commonly used, for example, in the printing of rotogravure sections of newspapers.

Such gravure printing, as usually carried out today, comprises the employment or an intaglio 25 printing-plate in which such ink-wells are allot thesame area but which vary in depth in conformity with the tones of the original interpreted, the wells representing the blacks of the subject being deepest, those corresponding to the lightest 3d tones being shallowe'st, and those'representing the intermediate tones being of harmonizing intervening depths. Since the deeper wells accomim ate a greater quantity of ink than the shallow r ones, the former, or course, ,willdepoeit 35 more'ink on the paper and therefore will produce darker tones. v

The image or design to be reproduced is transferred to the printing-plate by means of an intermediate medium, such as the so-called fcarbontissue, throughwhich the plate is etched'difl'erentially to produce the ink-wells oi varying depths, this being the only method employed commercially heretofore in making a gravure plate.

Such printing-plate is ordinarily produced by first making a continuous-tone negative of the subject and then making a continuous-tone positive therefrom, the positivebeing photographically printed on the lisht-sensitive gelatinous layer of the paper-backed carbon-tissue, and a rotogravure screen is also photographically printed thereover on the same light-responsive stratum of the carbon-tissue by a secondexposure. Such double-exposed carbon-tissue stratum or layer is thereupon secured face down on the sur- 55 face of the metal printing-plate, its paper backingltolthe darkest zones ing om's! such coating developed, the veloped coating being known in the trade as a carbon-resist". The dots in such carbon-resist representing the difierent tones oi the picture are all of the same size, which is determined by the equal areas of the screen open gs, but these dot areas, however, are unequally pervious to the etching fluid, depending on the tone of the zone of the subject interpreted. Etching-fluid then applied to such resist encounters less opposition or resistance at those portio s thereof correspondthe original subject and greater resistance at the lighter zones, and it accordingly produces a deeper etch at the former zones thanat the latter areas where more resistance is encountered, the resist being more or less broken down or despoiled by-the action of the etching agent thereon during such operation. Owing to the varying degrees of permeability or hardness of-the difierent sections of the resist due to their previous unlike light-exposures, an etchingfluid' of one specific gravity only cannot be.

employed to etch the underlaying plate through the resist with the required result.

Accordingly, in practising this procedure, five strengths of etching-acid are ordinarily used pro gress'ively, the one of heaviest specific gravity being used first, and, after this-has been removed, its action is followed upby those of successively less specific gravities. Expert judgment and capable discretion on the part of the etcher are necessary to determine the proper period oi action of each strength of the. etching-medium on the coated plate. After the etching has been eonipleted the carbon-resist is removed from the surface of the etched plate.

The above-specified procedure involves various details and features which are well known to a person skilled in the art, the indicated steps hav- 1113 been set forth merely by way of illustration and in order to aid in an understanding of the present invention and the ben'efitsaccruing from dts employment.

the plate and the etching then continued, it required, to the correct point, due to the fact that when the carbon resist becomes permeated or charged with the etching-fluid, its continued disintegration cannot be prevented, and, accordingly, great skill is required on the part of the operator to etch a plate having a given characteristic, and, the results cannot be duplicated with any degree 01' certainty. Furthermore, it is practically impossible to obtain an accurate registration of the one or more positives on the printing-plate because of the distortion introduced by the employment of the carbon-tissue in transferring the same to the plate. i

A process of producing an intaglio printingplate has also heretofore been suggested comprising photographing the subject in negative through a line-screen with the camera initially focused to obtain a checker-board effect of the screen on the ground-glass of the camera, overexposing such negative plate sufficiently to cause the shaded and dark portions of the design of the subject to appear on the negative as variable size, entirely-disconnected, transparent dots, the largest dots corresponding in tone and position to the darkest zones of the subject, such excessive or unusual light-exposure causing the negative, except for the dots, to be substantially opaque, and thereafter using this negative, through the" medium of a positive plate or film made therefrom, an etch-resist, and an etchingfluid to form the intaglio printing-plate; or, stated solids, to represent the darkest parts of the subject. In following this prior-art method, the half-tone screen is spaced at its correct focal distance in front of the sensitive plate which is to form the negative and the excessive lightexposure of the plate is depended upon entirely to lessen or restrict the effect of the screen so that the negative carries only in half intensity the tones of the original subject. In accomplishing this desirable result, however, the over-exposure eliminates all dot effects in the negative where the original subject was entirely white, so that the negative in those areas is completely We.

Whereas this procedure possesses merit and adapts itself forcertain lines of 1 work, such as textile printing, it has the disadvantage that the specified elimination of dot effects is not restricted in the negative to the completely white portions of the subject, but such dot absence applies also to the lighttones of the original subject, whereby this process does not result in the producabsence of dots.

tones of the original subject, those tones next to white necessarily being missing.

A leading purpose of the present new invention is to provide an improved method of printing in which the several above-specified and other disadvantages apparent to a person skilled in the art are avoided or eliminated, an especial object of the invention being to supply a different an better procedure to overcome the deficiency of the second of the prior art processes described, in that the new method is capable of making prints correctly and exactly representing all tones of the subject, from the lightest to the darkest.

Among the principal aims of the new invention may be mentioned (a) the provision of an improved intaglio printing-plate and the process of making the same, (b) the production of a print having novel characteristics, (c) the improvement of the deflniteness andregistration of the final point, (d) a procedure of forming printingplates which may be locaily strengthened or lightened as required to correct tone values, (e) a better method of composing a. plate incorporating printed matter, and (I) an improved process of transferring a positive made through a half-tone screen to an intaglio printing-plate. Various other objects and advantages of the" invention will be. made apparent as the natures of the details of the invention are more fully disclosed hereinafter.

In order that the novel intaglio printing-plate may have an ink-well formation in its printing surface capable of accurately representing all tones of the original subject, a positive transparency (hereinafter referred to as a positive) is made by photographing a continuous-tone negative of the subject through a conventional half-tone screen under such conditions of screenposition and of exposure that the dots on the positive are all of the same intensity but vary in area or size from the darkest to the lightest tones, the blacks or solids of the original subject being represented by practically unconnected dots and the whites of the subject being entirely free from dots in the positive, while the dots representing the intermediate tones are of correspondingly graduated areas. Although such a positive is made through an ordinary half-tone screen, nevertheless the positive is unique and differs from an ordinary half-tone positive in that the latter does not have the specified dot characteristics. This new positive displays only about one-half of the tonal intensities of an ordinary half-tone positive, that is to say, it has only about one-half the contrast or density of a conventional half-tone positive, and for that reason it has been deemed well to characterize it as a "hemi-tone" positive.

, Stated somewhat diflerently, a special or unconventional hemi-tone positive is made from acontinuous-tone negative of the original matter for use in forming the intaglio plate with which the printing is accomplished. In making this extion of a pririt in exact conformity with all tones ceptional or peculiar positive an ordinary halftone or similar screen is so associated with, or

placed at such a distance in front of, the lightsensitive plate or on which the positive is to be made and through which screen the light 4 is projected onto the plate, that the darkest part of the original subject, such as deep shadows, appear in this positive merely as intermediate checker-board or middle tones, and the remainder of the positive is comprised of all lesser tones graduating properly down to practically an This uncommon or unusual heml-tone positive, therefore, does not represent the originally-photographed subject correctly as to tone values, since it is much flatter in appearance because it incorporates only about one-half of the intensity or contrast of the original. This positive is unique in that, although it represents the entire range of tone values of the initial subject, all such values are actually present in the positive at about half intensity of the original, except pure whites which are the same in each. This peculiar positive is produced, not by over-exposure, but by placing the screen in front of the light-sensitive plate at the correct distance, differing somewhat from its true focal distance, to produce the indicated result.

The spacing of the screen in front of the photographic plate and the period of exposure of such plate are both less than would be used to produce an ordinary half-tone positive with all other conditions the same.

Even the making of half-tone plates as customarily practised today is in a measin'e a matter of trial due to the fact that the original subjects vary greatly, and heretofore there has been no satisfactory way of preliminarily evaluating them which would render predetermined procedure always feasible'or possible.

If in maldng the new specified hemi-tone positive the contrast therein is found to be too great to meet the conditions hereinbefore set forth, then the screen distance should be somewhat decreased, whereas if such positive has too little contrast to comply with the specification then a somewhat greater screen distance should be tried.

Under some conditions the screen distance may be about three-fourths that which would be used for the production of a half-tone and the exposure may be in the neighborhood of approximately one-third that which could .be satisfactorily employed for the making of a half-tone;

but it is to be understood that these factors are variable depending upon other features, such as the characteristics of the original subject, the intensity 9f the light, the speed of the emulsion, etc. a 7

One skilled in the art, however, will experience no substantial dimculty .in producing a hemitone positive having the properties referred to.

In this specification where the term tone-value or its equivalent has been used in reference to the original subject, it is intended to mean the relative position of the tone of any particular color in a scale which represents the full range of the color in question; when employed in relation to the continuous-tone negative, it signifies the value of the densityor opaqueness of the tone; when used in reference to the hemi-tone positive, it specifies the relation between the total area of the opaque dots to the area of the transparent surface in a unit area of the tone under consideration of the positive, it being home in mind *that all dots in the positive are of equal density regardless of size; and when employed in reference to the hemi-tone gravure printingplate, hereinafter referred to in more detail, it means the relation between the area of the inkwells to the area of the non-printing surface ina unit area of the tone under consideration in the printing-plate.

To compensate for the stated'absence of adequate and full-tone amplitude in this extraordinary hemi-tone positive, the etching of the intaglio printing-plate is carried out long enough to assure that the many practically independent etched wells in the surface of the plate are deep enoughtoaccommodatemilicientinksotbat when the printing is done there will be enough inkappliedtotheprintbyailwellstopermita proper spreading thereof whereby to give the print a full range of tone gradation from the darkest shadows or solids to the brightest highlights; this ink enlargement or spread of the dots on the print making good or overcoming the lack of full intensity of the positive. Such spreading of the ink on the print takes place in more or less degree for all printed dots.

One main reason for making and using such a singular or.unexampled hemi-tone positive is this: If the positive were made with tones of the exact values in the original, the ink-wells in the darkest portions of the etched metallic printingplate would either be run together intoexcessively large wells from which the ink-removing doctor-blade would extract their ink or their walls would be so thin that they would wear out unduly quickly with practically the same result.

Another, and perhaps preferable, vmode of practising the invention, which procedure is not however essential, but which has certain advantages of afl'ording more leeway or greater latitude in the time of light exposure in making the positive and of the production of sharper and more clearly defined dots and which may be accomplished by a slight change in the indicated distance between the screen and the film which is to form the positive, or by a slightly longer exposure, or both, comprises making a positive under conditions such that the whites of the subject have extremely fine dots in the positive which are capable of being entirely removed by an ordinary reducing operation, and, in eliminating these by such reduction, all of the remaining dots of the positive will be reduced a certain uniform extent, the specified reduction being controlled so as to remove the dots on the whites without entirely eradicating the dots representing the next darker shade. In this way, all of the tone values of the picture are preserved, although the positive, when viewed by itself, as stated above, shows less contrast and appears flatter than the original subject.

An additional feature of the invention is the production of a composite-positive of illustrations and type-matter in which the illustrations appear as described above and the type-matter is presented as black letters carrying crossed white.

lines.

A further principle of the invention resides in the transferring of the single or of the composite positive directly to the printing-plate without the use of carbon-tissue and in such a way that the subsequent etching can be easily controlled. To the accomplishment of this result, the surface of the printing-plate is coated with a resist of such a nature that it remains substantially unimpaired and intact during the entire etching period, whereby the etching may be interrupted at any time, the plate examined, and certain areas painted out with a protective varnish or the like, as desired, before continuing the etching.

Another aspect of the invention is present in the intaglio printing-plate itself, which possesses a non-printing surface corresponding to the whites of the picture and the remainder of which contains a plurality or ag egation of ink-wells representing the tone dots of the picture, these wells being of different areas and approximately uniformly etched as to depth, the wells representing the darkest tones being practically separate and distinct, the tones next to white being represented by small wells, and the areas representing the whites being entirely free from wells. All of the wells, however, are sufliciently deep to permit the plate to be topped, as by means of an ink roll-up, Without filling in of the liner wells, and re-etched as desired. As long as the kind of resist employed remains on the plate, such inking prior to re-etching is not required, but after the resist has been removed, the applied ink acts as a resist whereby the wells may be etched deeper.

Various other capacities and characteristics of the invention will become apparent as the same is more fully disclosed in the following detailed description and pointed out with more particularity in the appended claims.

More specifically, in producing the hemi-tone positive of the unconventional type, a continnous-tone negative is made from the original subject to be reproduced in the manner common in the photographic art; but if the original be a photograph, the negative from which it was made may be employed for this purpose, and in either instance, the negative may be retouched if desired.

For color work, a set of continuous-tone separation negatives, one for each color, is made photographically through color-filters in the usual way, and these are retuched or corrected as required so that each negative contains its proper color values.

Each negative, produced in this manner, is then placed before a camera, and while properly illuminated, is photographed through an ordinary half-tone or equivalent screen, the exposure being such and the screen being so positioned with reference to the positive being made that the clot formation is produced on the positive in which the largest dots, representing the blacks, are practically separate and distinct from, and do not touch, one another except possibly at their corners as in a checker-board efiect, while the smallest dots on the whites are so fine that they may be readily cut or removed in a reducing step. This desirable dot arrangement is obtained by selecting the proper distance between the halftone or other screen (for example 150 lines to the inch) and the sensitized plate undergoing exposure and using the correct lens aperture and time for the exposure.

This positive may be made on a wet-plate, if preferred. in order that the subsequent development thereof may be more readily controlled:

and, in the case of color work, when registration is particularly essential, each of the positives may be made by contact printing on a dry-plate using a half-tone or similar screen in a manner such that the above-mentioned dot formation is secured.

In either case, the positive is developed and then reduced by any standard reagent, depending upon the type of plate employed, and during this procedure the entire positive is reduced a sufficient amount to eliminate entirely or substantially completely the minute dots on the whites, but not enough to eradicate the dots representing any of the next darker tones of the picture, this ieduction step also tending to remove the fringe effect of the dots and to cause them to be more clearly defined and with sharper demarcation. This positive, however, will appear to have less contrast than the original subject or the negative, this characteristic being of material importance in the subsequent step of printing with the corresponding printing-plate, inasmuch as it provides a continuous support in the heavily inked gags of the plate for the ink-wiping doctor- Expressed differently, this peculiar and noteworthy hemi-tone positive is produced by using a half-tone or analogous screen at such a chosen distance from the light-sensitive film as to provide the specified result with proper exposure, the positive not truly depicting the negative from which it is made, because it displays the tones of the continuous-tone, preferably but not necessarily somewhat thin, negative in discontinuous dots of about one-half less value or area than they should be, the result being that such positive looks unduly shallow or more or less lifeless as it is without the full tone contrasts present in the corresponding negative. If such positive were made with a full gradation of tones and variations in density in complete and exact conformity with those of the negative from which it is made, then the portions of the plate etched therefrom presenting the deepest shadows instead of having a large number of independent nicely-walled-ln ink-wells would have relatively large areas of one well each and of such size that there would be substantial danger of the ink-scraping doctorblade scooping out their ink contents when it is wiping oil the excess ink from the remainder of the printing-plate. By making this positive such that the deepest shadows of the original subject are represented by conventional middle tones, in-

, stead of full black tones, there is the assurance that the ink-wells will be separate from one another with substantial intervening walls, the

latterfas indicated, precluding the doctor-blade from extracting the ink from the larger wells. It is necessary, however, to make amends for this lack of full or adequate tone amplitude throughout the positive, and, accordingly, when the plate is etched through a resist made from such positive, the etching is carried to a sumcient depth in the plate to permit each well to accommodate an amount of ink greater than that merely necessary to print a dot corresponding to the exact area of the well, the result being that after each such dot is printed its ink spreads on the print sumciently so that the final print is dense enough throughout to present a true and correct reproduction of the original subject. 7

From what proceeds, it should be cleamthat in the heml-tone positive-transparency the solids of the subject are represented by dots arranged in approximate checker-board design and it may be mentioned that when such dots are etched in the metal printing-plate the action of the etchingagent may round out the sides of the corresponding ink-wells somewhat but still retaining the general or approximate checker-board feature.

If a composite-positive of type-matter and illustration is desired, a positive of the type or printed matter is made by taking a press-proof of the printed matter, a negative is made thereof, a. negative of a gravure-screen is placed over the type negative, and a positive is photographically made therefrom on a film by contact printing, the resultant positive reproducing the type in black on which the screen appears as crossed white lines. This positiveis stripped and mounted on a glass-plate together with the hemi-tone positives of the illustrations in correct relative positions, thereby providing a suitable compoundpositive which can be placed in a vacuum printing-frame and printed on the light-sensitive surface of the metal printing-plate, as hereinafter set forth. The crossed white lines of the typematter in the final printing-plate perform the same function as do the walls of the larger wells in the etched printlng-plate in that they prevent the doctor-blade from removing the ink from the cells, representing the type-matter, or, stated otherwise, the white lines divide the typematter into practically separate dots in the positive and practically separate wells in the plate. The gravure-screen is preferably used in connection with the letters instead of the conventional half-tone screen because it provides pockets or wells in the plate of larger area resulting in a letter of sharper outline than it would be possible to obtain by the employment of a half-tone screen. Other screens, such as a line screen, may be used, if desired.

A single positive or a composite positive having been produced in the manner above stated, it will be understood that it can be transferred to the metal printing-plate in any standard manner and the plate then used for printing in accordance with the intagllo process, but this is preferably carried out in the following manner in conformity with the present invention: The surface of a copper-plate which is to form its printing surface is sensitized by applying thereto a lightsensitive coating of a solution of shellac and a bichromate commonly called cold-enamel." If the surface of the plate were covered with a thin coating of light-sensitive glue or gelatin, then exposed through a positive to the action of light. and then developed, the coating would be so thin that it could not successfully resist the action of an etching-fluid, and to bring out its full acidresisting properties it must be baked, Such a glue coatingis known in the trade as a glue top, and after the baking it is characterized as a glueenamel'. Inasmuch as the specified cold-enamel coating is adequately resistant to etching acid without the baking required for the special gluetop, the tendency of a thin plate, when heated, to buckle or warp is avoided, and, in any case, it would be difllcult to heat or bake a plate of large size properly and evenly. This unconventional and unprecedented herni-tone positive is photographically reproduced in such light-responsive cold-enamel coating. the positive having been previously stripped from its support and placed face down on the coating to assure that the flnal print will not be reversed right to left, whereupon such coating is developed, for example, as by the use of alcohol, leaving on the plate a coating impervious to the action of the etching medium but containing numerous free small passages therethrough corresponding to the dots of the positive and through which the etching fluid has free and unimpeded access to the surface of the copperplate. The positive design or picture is then etched through such resist apertures into the surface of the underlying plate to the required depth, a suitable single strength only of the etching agent being required, thus avoiding the necessity for the great care heretofore essential in etching gravure plates.

If a composite-positive obtained as above indicated is used. it is photographically printed on such light-impressionable copper-plate coating in any convenient manner, as by the step-and-repeat method of photo composition; or, in the case of a large composite, by a vacuum printing-frame, the

step-and-repeat procedure permitting an accurate tosecure registration of all parts of cooperating intagllo plates, this being particularly essential in the case of large subjects. Precise registration is facilitated by placing dependence on the employment for each color of the cold-enamel light-sensitive coating on its copper printingplate, which procedure entirely overcomes the normal and intrinsic uncertainties incident to the use of a deformable or distortable carbon-tissu such customary intermediate tissue agency employed in the production of gravure plates being subject to serious inaccuracies which prevent the securing of faithful reproductions, because the gelatin and its paper support of the carbon-tissue cannot be depended upon to aflord correct registration due to the vagaries of variable expansion with or across the grain of the paper, the humidity and the temperature, of course, entering into the situation.

Any areas of the printing-plate, whether single or composite, such as borders, to be protected from the action of the etching-fluid, may be preliminarily painted over with asphalt-varnish, after which the unvarnished parts of the plate are etched with a standard etching solution for a suflicient period of time, this operation requiring from three to eight minutes, depending upon the solution employed. Such etching may be interrupted at any time to permit the plate to be washed, dried, and examined, because the resist has remained in place in uninjured condition, and any portions of the plate that have been adequately etched may be painted over with asphaltvarnish before continuing the etching, which is then prolonged untfl the entire printing-plate has been etched the needed amount.

It is sometimes desirable to prolong the etching of the darker portions of the plate for a greater length of time than the lighter sections in order to produce ink-wells in those parts of the surface of the plate of depth enough to retain the required quantity of ink and all the wells should be etched to a depth such that the plate can be topped, if desired, for reetching after the coldenamel has been removed and a proof taken. The etching is terminated, however, before adjacent wells become connected with one another in any materialdegree through the breaking down of their wells. Such printing-plate may be cleaned and examined at any time and re-etched as required prior to the removal of he cold-enamel,

and, after the etching has progressed to the required point, the cold-enamel is removed by a strong cyanide or a lye solution and the plate is then ready for the printing-press. After a proof has been taken, the plate may be topped with ink and re-etched or corrected as needed, the ink, under thesecircumstances, acting as a resist.

In the finished, etched printing-plate, the various ink-wells are of different areas corresponding in position and size to the dots of the hemi-tone positive from which they were formed, but these wells are of approximately the same depth. It will be understood, therefore, that use is made of conventional disconnected middle-tone dots in the positive and corresponding conventional practically disconnected middle-tone wells in the printing-plate for thedeepest shadows and regular gradations from those to dot-free or well-free whites, as the case may be, which aredesigned and adapted to faithfully and correctly reproduce all the tonal changes of the original in the print.

Th centers of any four, adjacent, checkerboardarranged ink-wells, with their corners in close proximity, representing the solids of the sub- Ject, constitute the corners of a square and the distance between the centers of any pair of such ink-wells will be equal to the length of one side of such square or to the length of its diagonal, the former distance being necessarily somewhat shorter than the latter distance.

Considering the conventional gravure formation of ink-wells in the solids with their sides adjacent to one another, the centers of any four adjoining ink-wells also form a square and the distance between the centers of any pair of such wells may be equal to the length of the side of the square or to the length of its diagonal, the former distance obviously being shorter than the diagonal distance.

So far as stated, the two arrangements of inkwells are apparently the same when the centers of the wells only are considered, but, when the intervening nonprinting areas between the wells are examined, a material difference becomes at once manifest.

For example, the length of the non-printing portion of the printing-plate between wells measured along the diagonal line and the length of the non-printing portion between wells measured along the side-line of the square are substantially different, and, from the geometrical construction, it is apparent that the ratio between the two can be equal to, but cannot exceed, l.4142+ in the case of the standard gravure formation of ink-wells, leaving out of account any rounding out of the sides of the ink-wells during etching whereas, in the patentees approximate-checkerboard arrangement of ink-wells the ratio must inevitably be greater than 1.4l42+.

Again, this patentee's disposition or system of hemi-tone ink-wells, since they are all of approximately the same depth, conforms to the enerally-accepted, ordinary-half-tone formation, which is known to render a true tone gradation from solid to white and this does not apply to the commonplace, gravure, ink-well arrangement.

When this patentees inked plate in the printing operation, after its surplus ink has been wiped off by the doctor-blade, is brought into contact with the paper, which need not be of a superior grade but may be of the ordinary news- Paper kind, the ink 01 all these numerous wells is transferred to the paper and the ink of such multiplicity of printed dots spreads or expands on the surface of the paper in a manner to reproduce accurately and precisely all the tone values of the initial subject. It is the intention that the ink-wells in the plate representing the blackest or deepest shadows shall be of such size and capacity that, although they are practically unconnected, the spreading of their ink on the paper will be sufficient to cover the entire area of the printed surface corresponding to such portions of the subject, and the ink employed should be of such viscosity, determined by the depth of the etching and of the separation of the wells, that the dispersion of the ink on the printed surface will thus faithfully duplicate all tones and shades of the original.

By the employment of the present invention, with its non-requirement for the use of carbontissue, the prints are produced with exact reglstration for color work, with the minimum amount of labor, with the least complexity of operation, and with the fewest steps. These prints are outstanding and noteworthy in that a selected restricted range of tone dots is made use of to represent all tone values of the original subject, none being omitted and, although, in

desired.

the shadows, the conventional middle-tone dots are present as virtually or to all intents and purposes disconnected ink-wells in the intaglioplate, they are lost on the print through the spreading of the ink which produces a rich ink layer forming a desirable continuous tone.

Although the process set forth in detail above is one requiring reduction of the posit ve in the manner stated to remove the dots from the whites, it is to be remembered that this reduction is not necessitated by reason of an overexposure comparable to that referred to in one prior-art process and it is to be understood, furthermore, that the positives can be made in a manner to avoid the original production of dots entirely in the whites of the positive, and, accordingly, such a positive requires no reduction, although in such case the dots and the corresponding wells in the printing-plate may not be quite as sharp as if the reduction method were followed.

Summarizing, somewhat, some of the paramount advantages and cardinal benefits incident to the employment of the present invention, and which are of marked commercial value, are as followsz-Once a proper positive has been made and knowing the gravity of the etchingfluid, the temperature, and the time period for the production of a printing-plate therefrom, any number of such plates can be made which are, for all practical pu ses, exactly alike, 2. result heretofore incapable of accomplishment.

Again, persons of ordinary ability in the artmay practise the new procedure with gratifying results and without resort to the highly technical skill and careful Judgment which have been essential, in the past, in the making of gravure plates. Also step-and-repeat machines may be employed for composing the matter to be reproduced directly on the printing-plates. In addition, local re-etching of the plate, and continuation of the etching may be resorted to, if

Furthermore, faithful and exact reproduction of the original subject in the print is rendered possible of accomplishment with ease and facility.

These methods of practising the invention have been described for the purposes of illustration but it will be apparent to a person skilled in the art that various changes or modifications may be availed of and that the dlflerent features of the invention may be used in various combinations for the improvement of known printing processes. The invention is, accordingly, to be defined in accordance with the scope of the following claims when interpreted in view of the state of the prior art.

When the hemi-tonc positive is made from the negative by the direct contact method and a 150 line screen is employed, it has been found that the proper distance between the screen and the plateundergoing exposure is approximately .190 inch.

When such a positive is made in the camera, however, the operator adjusts the screen to secure a correct position thereof to produce a positive having the stated characteristics, but this does not mean that the hemi-tone positive will be like what theoperator sees on the ground-glass of the camera.

If the darkest tones of the subject are represented by quite small areas in the printing-plate, it is not essential that their ink-wells 'in all instances be entirely disconnected, the principal aim being to provide a printing-plate on which the ink-removing doctor-blade will have proper support at all times so that it may. eiflciently perform its functions without withdrawing an undue quantity of ink from any of the wells.

This application is a continuation in part oi my co-pending application, Serial No. 755,649, flied December 1, 1934.

I claim:

i. In the method oi making a hemi-tone positive-transparency for use in the preparation oi an intaglio printing-plate, the steps of spacing a screen in front of a light-sensitive photographic-plate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced for such a period 0! time, said space and exposure both being sufliciently less than would produce an ordinary half-tone positive-transparency with the other conditions the same, that the exposed plate, when developed, will represent the solids, ii any, of the subject at substantially one-halt tone value by relatively-large practically-unconnected dots and will represent all lesser tones of the subject by dots of corresponding lesser areas, and developing said exposed plate to produce a positive-transparency having said characteristics, all said dots being of substantially the same density.

2. The method presented in claim 1 in which said dots in the positive-transparency represent-;

ing said solids ii any are arranged in approximate-checkerboard design.

3. In the method of making a semi-tone positive-transparency for use in the preparation of an intaglio printing-plate the steps 0! spacing a screen in front of a light-sensitive photographicplate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced for such a period of time. said space and exposure both being suiiiciently less than would produce an ordinary hall-tone positive-transparency with the other conditions the same, that the exposed plate, when developed, will represent the solids, if any, oi the subject at substantially one-hall tone value by relativelylarge practically-unconnected dots in approximate-checkerboard design, all'lesser tones of the subject by dots of corresponding lesser areas, and the whites of the subject by zones having dots so minute that they may be readily removed by a reducing-reagent, developing said exposed plate to produce a positive-transparency having said characteristics, and reducing the dots of said positive-transparency by a reducing-reagent until the dots on the whites have been substantially-completely eliminated without eradicating the dots representing the lightest tone, all said dots being of substantialLv the same density.

4. In the method 0! making a hemi-tone positive-transparency for use in the preparation oi an intaglio printing-plate, the steps oi spacing a half-tone screen at such a distance in front oi a light-sensitive photographic-plate in a camera and photographing a continuous-tone negative of the original subject to be reproduced on said plate in said camera and through said screen with such a time-exposure of the plate, said screendistance and time-exposure being both sufllciently less than would produce an ordinary-half-tone positive-transparency with the other conditions the same, that the exposed plate, when developed, will represent the solids, ii any of the subject at substantially one-half tone value by relativelylarge practically-unconnected dots in approximate-checkerboard design and all lesser tones oi the subject by dots 01' corresponding lesser areas and developing said exposed plate to provide a positive-transparency having said characteristics all said dots being of substantially the same density.

5. A hemi-tone positive-transparency depicting a subject having tones adjacent to white, adapted for use in the preparation or an intaglio printingplate, representing the solids, ii any, of the subject at substantially one-half tone value by relatively-lar'ge practically-unconnected dots all lesser tones of the subject by dots of corresponding lesser areas, and the whites of the subject by practically dot-free zones, all said dots being of substantially the same density.

6. A hemi-tone positive transparency depicting a subject having tones adjacent to white, adapted for use in the preparation of an intaglio printing-plate, representing the solids, if any, of the subject at substantially one-halt tone value by relatively-large practically-unconnected dots in approximate-checkerboard design, all lesser tones of the subject by dots of corresponding lesser areas, and the whites oi the subject by practically dot-free zones, all said dots being of substantially the same density.

7. A hemi-tone positive-transparency depicting a subject having tones adjacent to white, adapted for use in the preparation of an intaglio printing-plate, representing the solids, if any, of the subject at substantially one-half tone value by relatively-large practically-unconnected dots, all lesser tones of the subject by dots of corresponding lesser areas, and the whites of the subject by zones having dots so minute that they may be readily removed by a reducing-reagent, all said dots being of substantially the same densiiy g hemi-tone positive-transparency depicting a subject having tones adjacent to white, adapted for use in the preparation of an intaglio printing-plate, representing the solids, ii any,

oi the subject at substantially one-half tone value by relatively-large practically-unconnected dots in approximate-checkerboard design, all lesser tones of the subject by dots of corresponding lesser areas, and the whites of the subject by zones having dots so minute that they may be readily removed by a reducing-reagent, all said dots being of substantially the same density.

9. In the method of making a hemi-tone i ntaglio printing-plate, the steps of spacing a screen in front of a light-sensitive photographicplate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced for such aperiod of time, said space and exposure being both suiiiciently less than would produce an ordinary half-tone positive-transparency with the other conditions the same, that the exposed plate, when developed to form a positive-transparency, will represent the solids, if any, of the subject at substantially one-half tone value by relatively-large practically-unconnected dots and all lesser tones of the subject by dots of corresponding lesser areas, all said dots being of substantially the same density, developing said exposed plate to produce a positive-transparency having said characteristics, and reproducing said dots approximately as inkwells in the surface of a printing-plate photographically and by etching.

10. The method of making a hemi-tone intaglio printing-plate as set forth in claim 9 in which said dots in said positive-transparency and said ink-wells in said printing-plate, representing the solids, if any, are arranged in approximate-checkerboard design.

11. In the method of making a hemi-tone intaglio printing-plate, the steps of spacing a screen in front of a light-sensitive photographicplate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced for such a period of time, said space and exposure being both suillciently less than would produce an ordinary half-tone positive-transparency with the other conditions the same, that, the exposed plate, when developed to form a positive-transparency, will represent the solids, if any, of the subject at substantially one-half tone value by relativelylarge practicallyunconnected dots in approximate-checkerboard design and all lesser tones of the subject by dots of lesser areas, all said dots being of substantially the same density, developing said exposed plate to produce a positivetransparency having said characteristics, exposing the coated surface oi a plate having a lightsensitive cold-enamel coating, capable oi remaining substantially-unimpaired after development and during and after the completion of the etching of the plate through apertures therethrough, to light through said positive-transparency, developing said exposed coating thereby removing the unexposed dot portions thereof, etching the bare areas 01' the plate through the dot openings in said developed coating solely by a single-strength etching-agent to form an intaglio printing-plate, and removing said coating.

12. In the method of making a print of the subject to be reproduced, said subject including tones adjacent to white, the steps of making a hemi-tone positive-transparency from a continuous tone negative of the subject through a screen under such conditions of screen-position and of light-exposure that all of the tones of the subject, except white, are interpreted in the positive-transparency at substantially one-halt value by dots of different areas, the solids, if any. of the subject being represented in the positivetransparency by relatively-large practicallyunconnected dots, the whites by substantially dot-free zones, and all intervening tones by dots of correspondingly-graduatedareas, all said dots being oi substantially the same density, exposing the light-sensitive coating of a plate to light through said positive-transparency, developing said exposed coating, etching the plate through said developed coating thereby forming an intaglio printing-plate having a surface with inkwells corresponding in areas approximately to the dots of said positive-transparency,.removing the coating from said printing-plate, inking said plate and removing the excess ink therefrom, and printing from said plate, said wells being etched to a depth to permit them to accommodate and to transmit to the print amounts "of ink suflicient to allow the printed dots to spread sumciently to compensate for the reduced tonevalues of theink-wells and to correctly reproduce the subject with all of its tones iniull in- .tensity.

13. In the method of making a print of a subject to be reproduced, said subject including tones adjacent to white, the steps of spacing a screen in front 0! a light-sensitive photographicplate at such a distance and exposing said plate through said screen to light controlled by a continuous-tone. negative of the subject to be reproduced for such a period of time, said space and said exposure being both sufllciently less than those which would produce an ordinary half-tone positive-transparency with the other conditions the same, that the exposed plate, when developed, will interpret all of the different tones of the subject, except white, at substantially one-half value, the solids, ii any, oi the subject being represented in the developed positive-transparency by relatively-large practicallyunconnected dots, the whites ot the subject being represented in the positive-transparency by zones having dots so minute that they may be readily reduced by a reducing-reagent, and all intervening tones of the subject being represented in the positive-transparency by dots of correspondingly-graduated areas, all said dots being,

of substantially the same density, developing said exposed plate to produce a positive-transparency having said characteristics, reducing the dots in said positive-transparency by a reducing-reagent until the dots of the whites have been substantially-completely eliminated without eradicating the dots of the lightest tone, exposing the coating of a plate, having a light-sensitive-coating capable after development of remaining substantially-unimpaired during and after completion of the etching through apertures therethrough, to light through said positive-transparency, developing said exposed coating thereby removing the unexposed dot portions thereof, etching the bare areas of said plate through the dot openings in said developed coating to form an intaglio printing-plate having a printingsurface with etched ink-wells corresponding approximately in areas to the dots of said positivetransparency, removing the developed coating from said printing plate, inking said plate and removing the excess ink therefrom, and printing with said plate, said ink-wells being etched to a depth to permit them to accommodate and to transmit to the print amounts of ink suiiicient to allowthe printed dots to spread sufllciently to compensate for the reduced tone-values of the printing-plate and to correctly reproduce all tones of the subject in their full intensities.

14. The method presented in claim 13 in which,

the dots of said positive-transparency representing the solids, it any, are arranged in approximate-checkerboard design, in which said plate light-sensitive coating is cold-enamel, and

in which the etching is performed solely by a single-strength etching-reagent.

15. In the method or making a positive-transparency for use in the preparation 01' an intaglio printing-plate, the steps of spacing a screen in front of a light-sensitive photographic-plate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced forsuch a period of time, said screen-distance and exposure both being sumoiently less than would produce an ordinary halttone positive-transparency with the other conditions the same, that the exposed plate, when developed, will represent the solids, it any, of the subject by relatively-large practically-unconnected dots and will represent all lesser tones of the subject by dots of corresponding lesser areas, and developing and fixing said exposed plate to produce a positivetransparency having said characteristics, all said dots being of substantially thesame density.

18. In the method of making an intaglio printing-piate, the steps oi spacing a screen in front of a light-sensitive photographic-plate at such a distance therefrom and exposing said plate through said screen to light controlled by a continuous-tone negative of the original subject to be reproduced for such a period of time. said space and exposure being both suiiiciently less than would produce an ordinary half-tone post-- ,n ting-plate phically and by etchin ?ai-Tent do. 2,155, l. .58

CERTIFICATE OF CORRECTION.

17. In the method oi makinga em-mm 1ntagiio printing-plate from a subject having tones adjacent to white, the steps of making a posi-r five-transparency representing the solids, it any,

of the subject at substdntialiyone-hal! tone-t value by relatively-large, practically unconnected dots in approximate checkerboarddesign and all lesser tones of the subject by dots of corresponding lesser areas, all said'dots being of substantialiy the same density, exposing the coated suriace of a plate, having a light-sensitive coldenamei coating capable after development of remaining substantially unimpaired during and after completion or the etching of the plate through apertures therethrough. to light through said positive-transparency, developing said exposed coating thereby removing the unexposed dot portions thereof, etchingthe bare areas of.

the plate through the dot openings in said developed coating solely by a single-strength etch-'- ing-agent to form an intagli'o printing-plate, and removing said coating.

J. WILKINSON.

April 25 1.959.-

- WILL AM J. WILKINSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction a?! follows: column, line 35, claim 5, for 'scmi- Page 7 first;

tone! read hemir-tone; and that the said Letters Patent should be read with this correction therein that the same may conform tov the record of the case in -Si9aed and sealed this 12th da of December,

(Seal) the Patent Office.

' Henry van'a rsdale, -Acting Commissioner of Patents.