US2171578A - Process for the reproduction of graining - Google Patents

Description

Sept. 5, 1939. F. L. LEE

PROCESS FOR THE REPRODUCTIONv OF GRAINING '.Filed May 26, 1937 Fos/ 7/ vs 770S/TIVE IVEGA 11v:

Pas/TI v5 POS/ T/ VE A/EGHTIVE m m m w Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE PROCESS FOR THE REPRODUCTION OF GRAINING 4 Claims.

This invention relates to processes for reproducing natural surface effects, pictorial effects, combination of designs and decorations, and particularly wood grains.

Certain varieties of wood are characterized by relatively complex and striking grain patterns, which it is especially desirable to reproduce on metal or other surfaces. Examples of these are English oak burl, Australian lacewood, quartered l0 oak, birds-eye maple, Sequoia redwood, burl walnut, and various hardwood crotches. Such grain patterns produce a visual impression aggregating three distinct effects, namely, (first) an effect of grain lines and stipple, (second) a wave or ripple effect, involving light, medium and dark shading or tone variations, and (third) a characteristic color effect.

An object of this invention is to provide a method which permits more tone value to be transferred from the resulting printing matrix plate.

A further object is to provide a matrix printing plate having main cavities of approximately equal depth, that give a low loss transfer of tone value 2:5 to the final offset and allow proportionate tone values to remain under pressure required in transfer.

Another object of the invention is to produce a matrix printing plate by a process adapting it to secure, by a single transfer operation, both the first and second aforementioned visual effects, and to combine them. in their true natural relation.

Another object is to provide a process for the 3 aforesaid purpose, which, when once performed, requires no repetition of early steps to secure any desired number of identical matrix printing plates.

A further object is to reproduce on a matrix ii-l plate, by a single etching operation, a pattern reproduction of the whole and complete visual appearance of the master pattern or sample to be reproduced, said appearance including the impressions of grain line and stipple and the im- 45 pression. of the wave or ripple effect, and to establish exact registration of these effects upon the matrix plate to conform to the specimen.

A further object is to produce a matrix plate that will more continuously portray a full tone 5!) appearance of the image of a wood specimen or other surface. It is found in processes including the etching of cavities below the plane of the metallic surface of the matrix plate, that (with the exception of those high light areas as dic- 05 tated by the natural surface copied), the unaltered top surface which remains between the cavities, deducts more or less from the continuity of the tone value of the specimen or master pattern in proportion to their expanse.

When a master pattern, the face of which is made up of small spots is viewed, the eye fuses the light reflection as a sense of tint. The eye is unable to readily distinguish these components but sees only their integrated effect. The size and number of these spots modifies the tint, the 0 smaller, more numerous and closer together they are, the stronger the tint. It is therefore highly desirable in reproducing a full toned image, to break up this surface effect, merging these spots to a certain limit, thereby effectively increasing 16 the continuous tone effect.

For example: In the photo engraving process gradation of tone is secured through the employment of a mechanical screen having equal lines and spaces, and placed as an obstruction between 20 the lens aperture and the sensitized taking plate. This process was originally developed for imprinting on a light paper background and produces, to a degree, the feeling of continuous tone by so-called typographic letter press printing and lithograph or off-set printing, but upon examination it will be noticed that tone value is less continuous than it would seem to be. If this photo engraving process is employed in making intaglio plates by reversing the negative, there is a very appreciable loss of tone value as compared with the full tone of the specimen, owing to the large expanse of top surface that remains between cavities.

And for example: In the photogravure process which was likewise originally developed to imprint on the surface of light background paper, the tone positive is screened by permitting the light to strike through transparent line rulings on a sensitized carbon tissue. These lines erase part of the image and in their aggregate, such obliteration very materially subtracts from the active image. If this process be used in producing intaglio plates, an appreciable loss will be seen in the final offset owing to the expanse of 25 top surface seen between cavities, thus introducing a loss in the image.

In my process, an absolute continuous tone photographic negative or a contact diapositive therefrom, or a reverse negative, photographed in) from. an original specimen surface, is transformed into an image that is only slightly minus in tone value from the absolute continuous tone value of the specimen. This process is capable of producing tone value with unusual definition of detall and with a truer feeling of gradation of tone, as well as more faithful interpretation of highlights which come out with clarity and pureness that gives striking contrast to the darker tone values in the composition of the image. After the transformation, the difference between the transformed image and the absolute continuoustone image taken from the specimen, results from a substantially unaltered top surface in. the final matrix plate, which surface is utilized as :a grid to keep the doctor blade on the surface plane of the plate. The structure of the upper face of the plate thus provided, is very finely divided and is closely related to the surrounding low-loss cavities, it being dictated by the specimen, eliminating the use of the usual mechanical grid of geometric design which grid always introduces considerable loss in any image in the formation of which the grid is used.

Thu upon transferring pigmented matter from the cavities of my matrix plate to the surface which receives the final offset, increased accuracy of the reproduction is evident because the continuity of the image is made possible by placing the cavities in close relation and connecting the cavities, one with another, (with the exception of those high-lighted areas) so that there are lesser and smaller spaces to be obliterated when the pressure of final imprint merges the material lifted from one cavity of the matrix plate into the material lifted from a neighboring cavity.

For the purpose of illustrating the several steps of my process, I have provided the accompanying drawing illustrating diagrammatically the several steps of my process.

If a wood specimen or master pattern I having prominent surface grain lines and stipple is to be simulated in appearance by the employment of my improved process, it is usually necessary to first suitably treat the natural grain surface to be reproduced. Ordinarily this surface is that of a veneer, which may be glued or otherwise suitably secured to a hardwood board, and then dressed down to present a smooth, fiat face clearly showing the grain of the wood. Upon such face, adjacent to opposite margins thereof, are impressed indentations, which, are preferably filled with suitable material to sharply distinguish them from their background. After waterproofing the bottom and edges of the block and the veneer edges, the grained face of the specimen or master pattern i is coated with shellac, and then waxed and polished.

The grained face of the master pattern is then photographed to obtain an ordinary negative 2 (preferably on glass), conforming exactly in its dimensions to the mastern pattern. Such. negative, accurately depicts the grain as regards the size, shape, and relative locations of the various spots, lines, or other definite markings, but fails, due to well known limitations of photography, to represent all of the true relative tone values of the pattern. Such negative may be quite faithful in general respects, but is not sufficient in itself to provide a-mechanical vehicle which will necessarily characterize the dominant values and gradations that are seen in the master specimen or pattern. An increased value may be had to improve the final appearance, by eventually adding to the image a stronger interpretation of the prominent grain lines and stipple and other values, by retouching the negative, and for use as *a guide in such retouchingit is preferred to now make from the negative, a positive print 3 on paper suited to receive and retain pencil or crayon markings for use only as a memorandum check.

All overtones of the wood specimen I are progressively noted and accurately indicated with crayon on the print 3, securing exact respondence of tone between the specimen and print in all areas, any unduly dark areas of the print being identified for future reference by color or other handwork.

The positive print 3, as thus prepared, serves as a guide in retouching the negative 2 by laying the print face down, upon a glass plate 4 having a strong light therebeneath with this negative superposed upon the print 3 and with the graining reproductions in an exact registry established by the aforementioned positioning marks. The emulsion face of the negative 2 is uppermost, and has cemented thereto a thin tissue 4a of transparent paper, suited to receive and retain crayon markings. With the negative thus illuminated through the retouched print 3, it is readily feasible to fill in with crayon on the tissue, all overtones indicated on the print and to subdue or eliminate, any blemishes appearing as overtones on the print. Also at this time, certain predominating grain lines and grain stipple are subdued, removed or stopped out, whereby the grain reproduction on the negative is substantially limited to the ripple or Wave effect and any whorl effects orother major variations of the master pattern. The retouched negative (formed of the negative 2 with the tissue 4a cemented thereto) is indicated at 2a.

The next step is to transform the continuous tone image of the retouched negative 2a into pure line and irregular specks, having equal opacity and density, which produce in their aggregate, an image of practically no loss. (Either an original continuous tone negative or positive may be transformed. The transforming of a negative will now be dealt with. to logically follow previous steps.) This step will be referred to as the transformer plate 5 which consists of a thick plate of glass, having a finely ground working face to which are initially applied several albuminous coats containing potassium silicate, and such initial coating, when thoroughly dry, serves to cause a sensitizing coating to firmly adhere thereto and is the basis for a finely reticulated surface due to its bichromated gelatin content, the importance of this effect appearing hereinafter.

Against the sensitized face of this thick glass transformer plate 5, there is now placed the retouched negative 2a, and light is transmitted through the latter to such face, and photochemical action takes place. The gradated and varied tones in the negative, prints or hardens the gelatin face as indicated at 5a in proportion to the densities of the varied tones. Where light has reached the sensitized face of the transformer plate 5, portions of the bichromated coating become more or less insoluble.

The plate is now washed to remove all traces of unaltered portions of the bichromated coating, and as washing continues, different parts of the coating absorb water according to the degree of light which reached it through the negative. This gelatinous coating appears to swell forming minute bubbles or proturbances, and is then allowed to thoroughly dry and when dry the face is found to have broken up into minute reticulations that vary in water retaining ability.

This gelatinous coating is now subjected to immersion in water for a short period, and then allowed to slowly evaporate. The coating is now partially dried and the effect of this treatment is that the gelatinous face has absorbed water throughout definite portions thereof as determined by the aforementioned exposure to light through the retouched negative The next step lies in inking the surface of the transformer plate 5, asby a suitable inking roller, said roller having been charged with opaque, greasy ink, isthen firmly pressed against the surface thus prepared and the ink adheres only to those completely insoluble portions previously affected by light. The inked image thus produced, becomesan effective transformation, of the continuous tone image on the retouched negative 2a, toa positive image of uniformly dense and opaque black and apparently continuous tone as viewed by the average naked eye, but in fact is interrupted by multitudinous minute, feathery open areas of irregular'size and shape, due to the aforementioned reticulated surface of the gelatinous'coating. Ink appears to adhere in a dense manner to the central part of the reticulations, some of which have cracked or opened, and is slightly less dense at the edges, all soluble portionscontain moisture, having refused to take the ink. This formation occurs in the deeper tones of the image, but for the lighter tones and high light areas of the image which are composed of lighter, frailer, smaller and fewer reticulations to a given area, the ink appears to adhere in a dense manner only to the central portions of the reticulations and is very much less in evidence at thefeathery edges. Thus such a transformer plate provides a highly accurate representation of the ripple or wave motion effect of the grained surface of the original Wood specimen to be reproduced, the form of its reticulations being directly controlled by th specimen itself. This transformed plate is now allowed to dry off for several days.

There will now be described a method of accurately reproducing the grain line and grain stipple effect of the wood specimen or master pattern treated as above described, and indicated at la;

To the grained surface of the specimen la is applied a liquid (preferably hot) of a nature to be rapidly absorbed by the softer surface portions of the veneer, namely, those portions within the pores and other grain depressions of the surface, but the simple application of water will accomplish' the same result, taking a greater period of time to swell up portions within the pores. A very effective solution for th s purpose includes caustic soda, wood alcohol, and paraffin. This solotion is continuously brushed back and forth on the grained surface until resultant swelling of the softer surface portions raises the same above the general surface level. These raised portions may now be wiped free of the surface by a brush or the like, the wiping operation being repeated at intervals until the grain lines and stipple are sufficiently lowered beneath the surface level. Treatment of the specimen la is now completed to produce specimen lb, by washing the grained surface with alcohol, removing the alcohol, thoroughly rinsing said surface with water, and finally allowing the specimen to thoroughly dry.

The next step consists in applying to the grained surface of specimen lb by adhesion, a thin uniform coating of a fluid or semi-fluid material such as will not readily penetrate the grain depressions. For this purpose engravers black proving ink may be thinly and evenly applied by an inking roller or other suitable means to the entire surface of the specimen, exclusive of its grain depressions, forming a negative pattern of such depressions.

From the specimen lb thus inked, there is taken under suitable pressure, an imprint on thin oiltreated translucent tissue, the uninked areas thereof forming an. accurate, sharply defined negative pattern 9 of the grain lines and grain stipple of the wood specimen lb. This pattern will be referred to as the grain line and stipple tissue negative 9, and will be added to the image.

It is now desirable to build up the density and choke up and partly close the feathery open areas of the transformer plate 5 and combine it with the grain line and stipple tissue negative 9. The transformer plate 5, containing the positive image of ripple and Wave effects, having dried off, is now contacted to a sensitized glass plate It] in a suitable vacuum frame and by photochemical action is reversed to a negative image ll on said plate with a gentle light source of a few seconds duration, which renders the less dense edges of the reticulations to benneficially choke up causing some of the particles to remain isolated and some to combine with their neighboring particles the glass plate it retains the full benefit of the previous retouching operation (performed on the original photographic negative 2a), it is desirable to also retouch said image ll to further increase the accuracy of reproduction and eliminate all fiaws and correct blemishes. Said negative image ll lends itself readily to manual addition and correction of tone values, as in its negative form it shows as opaque dense varied shapes of varying sizes, due to the linear composition of its characteristic formation on the positive ll] and the aforementioned granular breaking up of the image. After retouching, the above negative I l is contacted to another and final sensitized glass plate l2 in a vacuum frame, which further builds up the continuousness of tone (the position of register marks having been determined mechanically thereon) and by photochemical action the image is reversed to a positive image l3; and at once, and by a succeeding and similar operation the grain line and stipple tissue negative 9 is also added by contacting (with positioning marks located in perfect register,) to the final sensitized glass plate l2. The foregoing operations produce a double or superposed positive transparency (formed of the plate l2 with its positive image l3, and the tissue 9) of vastly greater continuous tone which has the complete image in opaque black on a transparent field of the original wood specimen with (first) the grain line and stipple efiect and (second) the ripple and wave effect combined. This final image thus gives all major and minor tone variations in close continuity, all in relation precisely conforming to the original master wood pattern. This final positive transparency may also he rctouched to remove minute blemishes or close open spots due to limitations of the felatinous coating.

The next step is to transfer the complete positive image of grain line and stipple and ripple and wave effects from this final transparency l2 to a metal matrix-forming plate Id. The latter, which is preferably sheet copper, has its working face first suitably cleaned and dressed, and upon said face is then dried sensitized enamel solution or the plate may be sensitized by the dry enamel process, or the cold top process or the bitumen process, all well known in this art.

The desired transfer is effected by exposing said sensitized coating on the matrix plate 14 to light through the final transparency, in a suitable printing frame. After the matrix-forming plate [4 is washed to dissolve soluble portions of the coating, the latter is hardened to a resistforming enamel. The metal exposed between interstices of such enamel now forms an accurate positive pattern of the grain lines and stipple of the wood specimen. Etching of this pattern into the matrix-forming plate is preferably ac" complished electrolytically, but the desired result may be approximated by exposure of the resistcoated surface to any suitable mordant.

After applying an acid-resisting lacquer or varnish to the back and edges of the matrix plate, such metallic surfaces of the face of the matrix as show through the negative enamel resist is thoroughly cleaned, preparatory to etching.

By immersion in a thoroughly hydrated iron chloride solution (or other suitable mordant) the plate is now etched, as dictated by the enamel resist and when properly conducted, the etching process is productive of smooth surfaces and straight walled grain cavities suited to readily receive and release greasy or fatty pigment or other coloring matter.

The resist-forming enamel is now removed by heating the matrix plate, then brushing its face with a solution of potassium cyanide and finally neutralizing the potassium cyanide by hydrochloric acid.

The matrix plate I4 is now completed, having been etched to carry two of the said three primary visual affects, namely, (first) that of the grain and stipple effect, and (second) that of ripples, waves and major and minor tone variations, all in a relation precisely conforming to the original specimen or master pattern I and with the image thereof imbedded below the surface in the metal.

The formation of the incised image does not include a geometrical design and in its positive sense is a cavity formation of naturally co-joined and relatively located depressions and is a composition of minute, irregular and jaggedly shaped depressions of varied form and of various widths in lateral dimensions, which depressions are con nected and disconnected cavity combinations and linear troughs as well as segregated and isolated spots of varying area sizes, down to minute areas.

Inasmuch as the matrix plate !4 of my process produces an image which includes a multiplicity of exceedingly fine divisions dictated by the master pattern, the image-print to be finally offset from said plate, clearly and accurately interprets the tone values of the original wood specimen, the exact appearance of which is to be reproduced, into terms of the breadth of a pigment rather than depth. Thus the final matrix plate has a variety of connected and disconnected cavities of different sizes and irregular shapes,

-- that are relatively located as to number, size and closeness, causing breadth of pigmented tone values (corresponding to the tone values of the original specimen) in proportion to the aggregate number of such cavities, etc., to a given area and approximately equal depths of such cavities.

Owing to the nature of etching with some mordants, an occasional very minute exposed area will receive slightly less etching as compared with that of a large exposed area during the same period of time, and as said broader areas etch deeper than areas of less breadth, and also etch to a substantially uniform depth, the tone value expressed by the cavities of equal depth asserts itself in the final print in terms of aggregation having physical breadth of pigment, thus giving greater tone expression to prominent grain lines and stipple,the first primary visual effect before referred to,and this is especially so where grain prominence is manifest in high light areas. This adds very appreciably to the realism of reproductions.

Use of this matrix plate in applying artificial grain reproductions to metal or other manufactured surfaces, conforms to well known practices, the plate being loaded with a suitable fatty or greasy pigment, then wiped to remove substantially all pigment exterior to the etched cavities, and a gelatin slab then rocked or rolled on the plate and then over the surface to be treated, to transfer the pigment from the former to the latter without material disturbance of the pattern.

Preliminaryto such use of the matrix plate, the surface to which the image is to be transferred, receives a ground coating of oil pigment to secure the (third) aforementioned primary visual effect, namely, that of characteristic color.

As no two species of the same wood genus are alike, and vast visual as well as structural differences appear in different kinds of wood and other surface effects to be reproduced, each subject presents a somewhat different problem in the way in which it may be best simulated in using my general process of producing matrix plates. I may vary the steps in simulating a specimen having grain lines that are less prominent and where a Wave, ripple or line effect is most pronounced. I may treat the wood specimen as previously described, with the exception that the two indentations or registry marks may be dispensed with, and except that previous to being shellacked, waxed and polished, the surface may be filled and rubbed with some dark material to give prominence to grain markings, thus dispensing with the preparations of the grain line and stipple tissue negative 9 previously described for making more prominent the grain lines and stipple. The grained face may then be photographed to obtain an ordinary negative which will, as the case may dictate, be subjected to the customary retouching.

The next step is to transform the continuous tone image of the retouched negative which image is the pattern of the whole, complete and general visual appearance of all grain line markings, by the method as outlined for the step referred to as the transformer plate 5. Subsequent steps follow those previously described including the etching of the matrix plate.

It is to be noted that in producing duplicates of any matrix plate, the final positive transpar ency may be again employed as described, elimihating any repetition of the prior portions of the process.

By the described process, the visual appearance of wood surfaces and other natural surfaces of intricate design and complex tone variations, may be reproduced with much closer simulation than has been heretofore achieved.

The term grain line and stipple in the following claims, designates any pattern of relatively small markings presenting the appearance of spots or lines, while any larger and more elaborate tone variations are included in the term Wave and ripple effect.

Having thus fully described my invention what I claim is:

1. In the production of matrix plates having the characteristic of presenting the grain line and stipple efiect together with the wave motion and ripple effect of the surface grain of a wood specimen, and wherein the plate in offset service produces an image print accurately interpreting the tone values of the specimen surface in terms of breadth of pigment rather than depth through the arrangement of the etched cavities of the plate, the method of preparing the master plate from which the matrix is produced, which method consists in first preparing the specimen surface for photographing with the naturalness of the surface maintained; photographing the specimen to produce a negative continuous-tone image of the surface to form the initial stage in the stage development of a positive plate; completing the positive plate by a stage development to cause the continuous tone characteristic to be transformed into an image of the ripple and wave effects with other major variations and with the image of reticulated characteristic; then treating the specimen to cause the grain lines and stipple effects to become of intaglio characteristic to form a printing surface; producing from such surface an ink-imprinted translucent issue negative in which the grain lines and stipple remain sharply defined and uninked; and then preparing a master plate by superposing the positive plate and translucent tissue negative in registration relative to a sensitized transparent plate; and exposing the sensitized plate through the superposed positive plate and tissue negative to thereby provide a combined image upon the transparent plate with the tonal effects of the specimen accurately portrayed and adapted to form the master plate employed in producing the matrix.

2. A method as in claim 1 characterized in that the stage development of the positive plate includes the following steps: cementing a thin tissue of transparent paper to the emulsion side of the negative and then retouching the negative by crayon or the like markings on the tissue to substantially limit the grain reproduction on the negative to such ripple, wave and whorl effects as may be present together with other major variations of the specimen master pattern to thereby form the source of a plate adapted for contact exposure; then transforming the image of the latter plate into an image of pure lines and irregular specks having equal opacity and density by contacting the plate with a transparent plate carrying a surface coating of sensitized bichromate colloid, and transmitting light through the image of such source plate to the face of the sensitized bichromate colloid coating; treating the image-carried colloid surface with water to cause swelling of coating content portions in accord with the light values controlled by the source image with the maximum light values producing insolubility of the coating; drying the transforming plate to thereby break the bubbles or protuberances of the swellings to thereby transform the coating face into a minute reticulation characteristic in which the reticulations vary in water retaining ability; immersing the transparent plate in water, then slowly evaporating water content and partially drying the plate to provide a coating having absorbed water throughout definite portions determined by the light values of the previous exposure; and then inking the prepared plate with opaque greasy ink to thereby transform the surface into an image in which the continuous tone image has been transformed into a minutely reticulated image of the ripple and wave motion and other general variation effects presented by the specimen surface and completing the positive plate.

3. In the production of matrix plates having the characteristic of presenting the grain line and stipple effect together with the wave motion and ripple effect of the surface grain of a Wood specimen, and wherein the plate in offset service produces an image print accurately interpreting the tone values of the specimen surface in terms of breadth of pigment rather than depth through the arrangement of the etched cavities of the plate, the method of preparing the master plate from which the matrix is produced, which method consists in first preparing the specimen surface for photographing with the naturalness of the surface maintained; photographing the specimen surface to produce a negative continuous tone image of the surface; subjecting the negative to treatment to render the effective image dominant as to ripple and wave effects while preserving the continuous tone characteristic; producing an image of minutely reticulated characteristic from the treated negative by contacting under exposure relation conditions the treated negative with the sensitized bichromate colloid coating of a transforming plate and exposing the coating by light transmission through the negative and thereafter developing the transforming plate to thereby produce an image of pure lines and irregular specks having equal opacity and density; applying an opaque, greasy ink to the developed transformation plate to form a positive image; producing a negative therefrom and subjecting it to retouching activities, and from it producing a positive plate of the ripple and wave effects of the specimen; additionally preparing a separate negative of the grain and stipple effects from the specimen; and thereafter preparing a master positive plate from which the matrix is produced by superposing in registration the prepared positive plate and the separate negative under exposure relation conditions relative to a sensitized glass plate to thereby combine thereon the separate images to form the master plate.

4. A method as in claim 3 characterized in that the separate negative is produced by the following steps: treating the specimen surface with liquid to swell the softer portions of the surface and raise them above the level of the harder portions of the surface to thereby gradually develop the grain lines and stipple effects of the specimen to become of intaglio characteristic, then inking the non-depressed surface of the specimen and applying thereto a thin oil-treated translucent tissue to thereby obtain an imprinted accurate sharply-defined negative pattern of the grain lines and grain stipple of the specimen surface and which forms the said separate negative.

FRANK L. LEE.

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