US2373489A - Halftone photoengraving process - Google Patents

Description

1 1945- w. s. MARX, JR 2,373,489

HALFTONE PHOTOENGRAVING PROCESS AND SCREEN Filed Oct. 18, 1941 .331 5 1 wlllliiill i lilim ll": l I I I .MIIIM ||||ll Q ||l..

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Patented Apr. 10, 1945 nALrroNs PHOTOENGRAVING PROCESS w Ann SCREEN 1' Walter S. Marx, J12, Santa Barbara, Calif., as-

signor to Printing Arts Research Laboratories, Inc., Santa Barbara, Calif., a corporation of Delaware Application October 18,1941, Serial No. 415,530

7 lClaims.

This invention relates to an improved halftone photoengraving process and an improved halftone screen for use in such process.

One of the objects of the invention is to provide to give printed illustrations which are characterized by the absence of screen pattern in the highlights, by clean solid lines and type devoid of screen pattern, and shaded portions which are reproduced with thaid of the screen pattern as dots depending for sizeupon the shading of the original artists drawing. In other words, by the aid of this screen and this process, I am enabled to make reprodnctions of artists drawings in.

which the shaded portions are reproduced in substantially conventional halftone photoengraving manner but in which lines and type are free from screen pattern and in which the highlights are completely free from screen pattern.

By a slight modification of my process, I are enabled to introduce a slight amouht of screen pattern into the solid portions of the printing plate while at the same time preventing encroachment of screen pattern upon the line and type elements.

An artists drawing comprises the following elements; First there is solid color which will hereinafter he referred to by this term. Second, there are highlights which are free from pigmerit. Third, there are shaded portions which differ in degree of intensity of the pigment. Fourth, there is line. Line" can be regarded solid color of small width; Nevertheless, wing to the fact that it is preferred in printing plates to have a small degree of screen pattern in solid color,. and further owing to the fact that one of the principal objects of the present invention is to prevent the occurrence of screen pattern in line, it is necessary clearly to dii ferentiate between these two elements of a drawit will be understood 'that line is intended to include solid lines which the artist may use in making the drawing and also legends, numbers, and the like, which are referred to briefly as"type.

In generaltenns, my invention involves the employment of two different kinds of light or, to he more enact, lighting of two ranges of wave length. The plates employed are sensitive to both kinds of light. My improved screen is provided with rulings or pattern composed of lines which are transparent or substantially transparcut to one kind of light, while they are opaque to the other kind of light. The drawing .or me.-

lit

terial to be reproduced is either prepared or treated so that the shaded portions thereof are made opaque to that kind of light for which the screen pattern is transparent.

In actual practice it is preferred to employ visible and ultra-violet light as the two kinds of light and it is further preferred to make the screen with lines or pattern which are transparent to ultra-violet light and which are efiectively opaque to visible light, or, more particularly to visible light having substantial actinic effect upon the photographic plates employed in the photoengraving process.

The employment or ultra-violet and ordinary light is particularly advantageous in the preparation of the drawing, since the artist can, as will hereinafter he explained, employ pigments and colors which appear the eye similarly to pigments and colors heretofore used. The pigments or colors may, however, as will hereinafter be described, contain material which renders them quite opaque to ultra-violet light. Consequently, the shaded portions will be quite onaque to ultra-violet light although to the eye of the artist, or indeed to the eye of any observer, they appear to he normal shaded The drawing prepared in this color" and line hath of which opaque to both visible and t lt However, the shaded portions? opaque to ultra-violet light. 1 t of the process, a negative is pre aid of the screen and with the violet and visible light. As indicated alcove, my improved p-rocessir revents occurrence of screen pattern in the line, and unless additional steps are taken, the s d color" will likewise be devoid oi screen Since this is frequently considered objection r printing purposes, additional steps may men to f -rovide screen pattern in the "solid color while maintaining the line devoid oi such pattern.

Other objects, advantages and capabilities of the invention will appear from the following" spe cific description of preferred embodiments there-- of taken in conjunction with the aeccompanying drawing in which:

Fig. l is a plan view of a screen embodying my invention;

Fig. 2 is a plan view of one which my screen is fabricated;

Fig. 3 is a cross-section of plate shown in 2; t

Fig. 4 is a similar cross-section of the modified has solid clacl: or violet light.

tlalll the plates from formof plate;

which is to been greatly enlarged from small portions of a drawing and negatives actually produced photographically. Indeed, all the iigures'of the.

drawing are greatly enlarged.

My improved screen which is shown in Fig. 1

asraasc it in the form of dyed gelatine upon the surface of the glass plate. It may herebe noted that if gelatine is used for the base of the line it, a water solution of fuchsine will dye it. In the case of the other plastic materials mentionedya water and alcohol solution of fuchsine may advantageously be emmay suitably consist of two sheets of glass which support between them lines it and ii of material which is substantially opaque to the actinic portion of ordinary light and which is substantially transparent to ultra-violet light. The lines i0 and iiare arranged in intersecting relation and they are preferably located at right angles.

to each other and in oblique relation to the major dimensions of the screen.

The two. sheets of glass'are secured together Ployed.

It is to be noted that whil I have successfully used fuchsine, it will be understood that any other clye,'or indeed any other material which transmits ultra-violet light and is substantially opaque 'to actinic visible light, may hev used instead of i'uchsine.

It will or course be understood that materials other than -fuchsine may be employed. Other materials which are efiectively transparent to with the aid of Canada Balsam or other suitable cement, or with the aid of any'other suitable securing means, so that the lines it and ii are in contact and in sandwich relation to the two sheets of glass.

In Fig.- 2 I have shown one sheet of glass having the lines is thereon. The lines to and it Referring to the embodiment of Fig. '3, the

grooves 052 may be-rnade with a diamond cuttin device, the depth of the grooves being suficient to allow for a deposit of a transparent resin or gelatinous material capable of transmitting near ultra-violet light, while absorbing visible actinic light.

Gelatin or polymerized methyl-methacrylate, commonly known as Lucite, or Plexiglass, or indeed any medium which is transparent to ultraviolet light and which will carry the dye employed, may be used as a iilling medium for the grooves it. These materials may be dyed with a pure grade of fuchsine and they then transmit light below 4,000 angstrom units and efi'e'ctually absorb light between 4,000 and 6,000 angstrom j veniently formed photographicaily from a master screen. The first step is to expose and develop aphotographic plate so that the screenrulings appear as a silver image in the gelatine. A suitable dye such as iuchsine is substituted for the reduced silver in thegelatlne coating on the plate by methods known in the art. The remaining undyed gelatlne maybe either removed or.

allowed'to remain between the dyed screen lines.

In Fig. 4 the gelatine in"whi ch the silver was not reduced is shown removed, leaving only the lines.

ultra-violet light-and-eflectively opaque to the actinic portion of ordinary light includenitroso-dimethylaniline, methyl violet, glass or gelatine suspensions of nickel and cobalt salts, and suspensions of cobalt chloride, copper sulfate, acetamine scarlet B.

It will be understood that the lines i0 and H may be of any desired number as in conventional screens. Thus, the number of lines may be be-' tween 50 and 300m the inch. r

The. artists drawing, a fragment of which is; shown on enlarged scale in Fig. may be prepared in the usual way, with the addition that the shaded portions are treated so as to be opaque to ultra-violet light. This treatment should not affect the appearance of the "shaded portions? to the eye so that the artist may visually obtain the desired shading which he desires to appear in the final reproduction. Furthermore, the shaded portions must maintain their relation to actinic visible light so that they may register selectively upon the negative in accordance with their density on the original draw-- ing.

The most convenient way of making this orig-- inal drawing having these optical requirements. is to mix with the pigment employed by the artist a material which is transparent to ordina light and which is opaque to ultra-violet light. Thus,I may proceed, as far as the making of the original drawing is concerned, in the manner described in my Patent No. 2,191,939, issued February 27, 1940. As stated in that patent, Inlay use an ultra-violet absorbent substance, preierably of the fluorescent type, such as quinine bi sulfate. The quinine bisulfate is dissolved in we'- ter and the solution is used as a solvent for the water-color or ink pigment used to make the v Distilled water cc 1000 Quinine bisulfate grams 00 Sulphuric acid, C. P cc 10 Egg albumen, C. P grams 15 The sulphuric acid amplifiesthe fluorescent and absorption properties. The egg albumen facilitates the smooth application of the pigment to the drawing. This solution is used instead of water as amedium for the artists pigment. The

pigment may be of any usual type; for example, it may be Windsor Newton's water-color Lampblack which is representative of the type of materialcustomarily used in making wash drawings.

It will of course be understood that I 'do not intend to limit my application to quinine bisulfate since any other material, transparent to ordinary light and opaque to ultra-violet light, may be employed. Other materials which may be substituted for quinine blsulfate to provide opacity to ultra-violet light include the following: anthracene, phenanthrene, various forms of naphthylamine disulphonic acid, beta. methyl umbelliierone, and para-hydroxy benzaldehyde.

The drawing is shown illustratively in Fig. 5,

" areas I; being highlights, area H being a light shaded" portion, area I being a heavier shaded portion, area I8 being a line, and areas "being type" considered as line. The drawing will also include relatively large areas of solid color (not shown) but the optical behavior, unless additional steps are taken, is the same for solid color as for line.

A part from the light which will be discussed hereinafter after. the procedure of making the negative with the aid'of the artists drawing and employing-my improved screen described above, may be effected in the normal manner. Thus, the negative may be placed in a photoengraving camera, my improved screen may be located in the camera at the proper distance ahead of the plate, and the drawing which is to be copied is placed on a suitable support and illuminated by light. For

the purposes of the present, invention, the light must contain ultra-violet light and visible light. Suitably all the light is derived from a single source which supplies both kinds of light. However, the invention is not to be considered limited in this respect because two separate exposures may be made, one in which the positive is illuminated by visible light, and another in which the positive is illuminated by ultra-violet light. The result is the same in both cases.

Such a source for a visible light and ultra-violet light may suitably be any of the ordinary white-flame carbon arcs which radiate amply in the ultra-violet region and also in the visible region. I may also use a lamp manufactured by the General Electric Lompany oi.Los Angeles, California, which consists of a high-intensity 'mercurywapor argon-filled arc lamp in a double none}; or quartz nonex envelope. Light rich in ultra-violet is generated by electronic disturbances between two barium oxide coated cathode elements in the inner tube. The now popular mercury vapor lamps may also be used as an efiective light source.

Considering the ultra-violet light-lit will be understood that the picture reflects no ultra -violet light from the line portions l6 and ill, no ultravioletlight'irom "shaded portions id and it), and no light from solid color portions. The highlight portions l3 reflect the ultra-violet light and that ultra-violet light passes directly through all portions of the screen corresponding thereto.

Thus, referring to Fig. (5,.it will be noted that the area of the screen including the lines it and it, as well as the open screen spaces between the lines around the letter F, is completely transparent to ultra-violet light. The same goes for the upper highlight portion 53 between the line iii and the two shaded portions i l and it. It will therefore be understood that on the negative (Fig; 7) there are two portions corresponding to the highlights it; which are completely exposed by the ultra-violet light alone. By "completely exposed is meant that when the negative is developed, there are two solid black portions constituted by reduced silver which portions correspond completely to the highlights i3. It is to be noted that these portions corresponding to the highlights l3 are completely devoid of screen pat tern because the exposure from the ultra-violet light alone is sufllcient completely to expose the portions of the plate corresponding to these highlights.

Now to consider the action of the ultra-violet light upon the shaded portions l4 and l5-it will be noted that owing to the presence of an absorbent for ultra-violet light, these two "shaded portions behave with respect to that light precisely as if they were solid black. That is, no ultra-violet light is reflected by the shaded portions" l4 and I5 (Fig. 5) and consequently what ever screenv pattern is produced on the negative corresponding to these areas results solely from the visible light or the visible component of the light. I

To consider the visible light or the visible component of the lightThe visible light striking the shaded areas" l5 and i5 is reflected thereby in amounts depending upon the degree of shading. Thus, the portion it! being slightly shaded, reflects strong visible light which strikes thescreen in the manner shown in Fig. 6.

Now, as has been described previously, the screen is areal operative screen for visible light. The'lines W'of the screen are opaque to visible" light and consequently the normal screen action occurs in the negative (Fig, 'I). The light shaded" portion i l gives lalrge overlapping dots of reduced silver as shown in the upper left-hand corner of fig. 7, while the heavily shaded portion it gives small dots corresponding to the openings in the screen as shown in the right-hand top corner of Fig. 7. Thus, the shaded portions print on the negative (Fig. 7) in the usual manner.

As has been previously pointed out; the visible light reflected by the highlight portions it does not affect the corresponding portions of the negative (Fig. 7) for the reason that the ultra-violet light reflected from the highlight portions l3 passes through the corresponding portions of the screen as if it were fully transparent. The visible light reflected from the highlight portions l3 'may tsnd to form some screen pattern corresponding tothe highlights id but this tendency is completely destroyed owing to the fact that the ultra-violet light corresponding to the highlights i3 renders the corresponding portions of the negative (Fig. 7) completely black in the developed negative.

Qne outstanding effect of my invention is that the line and solid color are not ragged around the edges due to encroachment on the "line" or solid color of diffraction or lens action of the screen. Tl'ius, consider the line it and particularly the right-hand end of this line." It will be noted with reference to Fig. 6,

that this line passes across an opening in the screen. If we consider thiscpening, it will'be seen that a certain amount oi? visible light falls through it above and below the line it. It

- would be assumed that this opening would act as a lens and tend to form on the negative (Fig. 7) a black dot which would lie across the white image of the line ill on the egative. This dei initely dots not occur in in cases and I attribute this result to the fact visible light alone admitted through this opening, or rather the part of the opening referred to which is obscured by the line it, is insuiificient to activate the silver at this point. This dot-forming action or tendency is not at all assisted by the ultra-violet light or the ultra-violet component of the, light. Ultra-violet light finds the screen to be merely a transparent plate so that the ultra-violet is not in the least difiracted.

Irrespective of whether or not this explanation'sets forth-the true cause of the result mentioned, the fact remains that fig. 7 is a reproduction malny-times'enlarged of adrawing similar to Fig. and it will be noted that perfect def initionof the "line" it and the "type" i? is obobtained in the metal printing elementderived therefrom.

Fig. 8 isan enlargement corresponding to Fig. 'I of a negative produced according to standard practice, the degree of enlargement being the same in both cases. The manner in which the fine line is lost and the sharp contour of "type is completely obliterated, will readily'be seen from Fig. 8.

It is'apparent from the previous description that solid color is reproduced in the negative in exactly the same manner as the line." The marginal definition of "solid color" is perfect and there is a complete absence of screen pattern within the solid color. It is rreque'nthv a necessity for good printing that solid color" (and not line. or typefb should be provided with screen pattern to a very slight degree to prevent subsequent deposit of excessive ink on "solid color".

areas when the finished plate is printed. This may be done by flashing the "solid color areas, to

a' very slight extent. This flashing has no efliect' I upon" the "shaded portions because it merely re-' sults in the formation of small or incipient dots which are completely masked by the larger dots as a result of normal exposure of the "shaded portions to the visibie light or the visible comp'onentof the light. Ordinarily, however, it is important and desirable that the sharp definition of the line and the absence therefrom of any encroachment of screen pattern should be very carefully preserved.

Flashing may be effected simply by placing a layer of tissue paper over the drawing of Fig. 5, and then drawing on. the tissu paper in black, matter corresponding .to the line" is and the "type II. This may be done quite roughly provided the roughlyapplied color does not overlie solid color portions of considerable size and in which it is desired to create screen pattern. The

plate is then given a very small exposure with the lensstopped. down and with visible light only.

- The degree of thisexposure is'merel sumcient to give a certain amount oi.'- screen pattern in the large solid color" portions. The tissue paper is then removed and t e exposure of the negative is proceeded with in he manner described above. Of course it is not to be deduced from the foregoing that it is necessary to do-the flashing before the exposure since it will of coursebeclearly ap- -Although my invention has been described in connectionwith specific detail o'f-the embodiments thereof, it must be understood that-the in-' vention is not intended to be limited thereto except in so far as set forth in the accompanying claims.

Having thus described my. invention, 1: declare that what I cla'imis: l'..In the art of halftone photo-reproduction,

the steps which consist in photographing a subject, theshaded portions of whichhave been rendered absorbent of ultra-violet light, onto a tained'in the negative and can of course be light-sensitive plate through a halitone screen. the line elements of which are transparent to ultra-violet light and substantially opaque to visible actinic light.

2. In the art of .halftone photo reproduction,

the steps of treating the shaded portions of matsorbent of ultra-violet light, photo-graphicallytransferring light from said matter to a lightsensitive. plate through a halitone screen havi line elements opaque to visible actinic light and transparent to ultra-violet light.

4. In the art ofhalftonephoto-reproduction,

- the steps of including in the work areas oi a drawing to be reproduced, an absorbent of ultraviolet light, transferring ultra-violet and visible light from said drawing through a halftone screen onto a light-sensitive element, said halitone screen having line elements opaque to visible actinic light but transparent to ultra-violet light.-

5. The method of photo-automatically producing a negative from a' pictorial representation,

which negative has highlights without screen not tern, shaded portions with screen pattern, and line portions without screen pattern and without screen-pattern deformation, which consists inrendering the'work areas of said pictorial representation absorbent of ultra-violet light, and photographically exposing a plate to form the negative by means of visible actinic and ultraviolet light through a screen having line elements opaque to actinic visible light and transparent to ultra-violet light.

6. The. method of photo-automatically producinga negative from a pictorial representatiom which negative has highlights without screen pattern, shaded portions with screen pattern, line portions without screen pattern and withoutscreen-pattern deformation, and solid color with slight screen pattern, which consists in rendering the worlg areas of said pictorial representation absorbent of one kind of light, photographically exposing a plate to form the negative by means of said kind oi. light and another kind of light through .a screen having line elements opaque to last said kind of light and transparent to first said kind of light, and flashing the negative slightly with the exception of line portions.

Darent'to those skilled in the art that th order 0f exposure is quite immaterialr r tern, shaded portions with '7. The method of photo-automaticall producing-a negative from a pictorial representation,

which negative has highlights without screen paten pattern, line portions without screen pattern and without screen-pattem deformatiom-a'nd solid color with slight screen pattern, which consists in rendering the work areas of said pictorial representation I absorbent of ultra-violet light, photogr'aphically exposing a plate to form the negative by means of visible 'actinic and ultra-violet light through a f screen. having line elements oqaque to actinic visible light and transparent to ultra-violet light, I and flashing the-negative slightly with the exoeption of line portions.

WALTER S.. MARX, Jn

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