US2179014A - Method of color correction of photomechanical images - Google Patents

Description

NOV. 1939- v R; L; KLEIN 2,179,014

METHOD OF COLOR CORRECTION OF PHQTOMECHANICAL IMAGES Original Filed larch 20, 1955 FIG. 6.

FIG-l0.

I N V EN TOR. FIG. fiderl Alf/e172 FIG.

x This is acdiv'lsion of my copending Patented Nov. 7, 1939 METHOD COLOR-CORRECTION OF PHOTOMEOHANICAL IMAGES Robert L. Klein, Cincinnati, Ohio Original application March 20,1935, Serial 19o.

12,032. Divided and this application October 21, 1937, Serial No. l'l0,21l

application ""Seri alnumber 12,032, filed March 20, 1935.

- The present invention relates to the color correction of half tone negatives used inthe preparation oblithographic color plates and has for an object the pmvision of novel method and means thatlwill enable the process artist to do a1l.work on the negative and to quickly and efiectively produce corrected photo-lithographic negatives that produce results equal or superior to anything that the engraver can produce with his engraving plates.

Another object of .the invention is to provide a method andmeans whereby the process artist can with a minimum of time and effort modify the color printing values or tonalities of negatives of all kinds that are employed in lithographic work, including the dot etching of masses on the negative from 'a solid color to a pin dotor vice versa.

Another object of the invention is to provide a method and'means whereby the tonality corrections .by the process artist on'the negative are permitted to remain permanently on the negative so that the plate maker may print the negative on paper or zinc without removing any portion of the materials applied by the artist and whereby these materials remain as a means affording a P tion prints may be done on a small negative,

high degree of protection for the preservation of the negative against atmospheric and other deteriorating conditions.

Another object is to provide a method and a system .of opaque and transparent staging solutions that aiford the process artist a maximum of facility and speed in preparing negatives of this character-for the plate maker as well as for permanently preserving the negative for future reprints on zinc.

Another object of the invention is to provide a method and means whereby all work on projecthereby eliminating crayon work after the print on zinc is made- These and other important objects are attained by the means and method hereinafter described and schematically illustrated in the accompanying drawing, inwhich: 1

Figs. 1 and 2 represent greatly magnified schematic illustrations or the penumbra or shadow thatappears around the half. tone dots on the negatives: l

Fig. 3 illustrates schematically a single magnifled. and unclarifled half tone dot with its" penumbra.

whenused in a bright light.

Fig; 5 is a view of the negative as shown in Fig. 4 when the same is held in a subdued light,

showing the edges of the individualdots as they plates.

Fig. 4 is an enlarged representation of the half tone pattern or mass on a negative as'it appears 10' Claims. (CI. 95-51) appear to fade into the penumbra and lose their corner to corner connection.

Figs. 6 to 11 form a continuous schematic view showing the steps of dot etching of the invention froin a solid color to a pin dot and reverse on a 5 negative, these views further representing the negative as being one-half staged with the staging chemical solution of the invention having a one-quarter tint of dye therein, and the. other half etched with acids- In the following disclosure the term "negative as used in a'general sense includes dry plates,.

wet plates, films and even screen projection negav tlves, in other words, all negatives employed for preparing color plates in the so called photolithographic process work that always require the efforts of a process artist in, correcting the color printing valuesor tonalities of any such negatives.- In its broad aspects v the invention herein includes a method and means .constituting a dot etching system of correcting half tone negatives,- staging the same with staging solutions and chemical resists, etching and re-etching with acidswhereby the process artist has complete a control of the tones to be corrected to the same extent as the photo-engraver has with his copper This includes the etching or reducing where necessary from a pin dot. to a solid mass or reverse and alsothe intensification-of tonalities wherever desired by the application of water and acid resisting transparent staging solutions containing aniline dyes of colors to produce the necessary corrected color printing values onthe negative; and also the staging with a clear transparent acid resist stagingcompound to retain any corrected masses against further reduction. The methods employed by the process artist 'in correcting half tone negatives have heretofore required a considerable amount of time and set with numerous aggravating difliculties. The purpose of the present invention is to minimize the difllculties and to reduce the cost of production of-such negatives in time, money, and labor 'from thirty-five to forty percent, and to further enable the process artistin many instances to reduce the number of color plates required by reason-of vastly superior negatives such, for example, as would enable the lithographer to produce what has all along required a seven color job in only four colors, thereby further and materially reducing the cost of the job. The same, advantages apply to all negatives that are used for any purpose in lithography such ,as continu-e ous tone positives,'etched positives, etched and staining contact positive direct orcontact nega- Itive printing, projection work from small negatives that are enlarged and printed on zinc, and

tedious painstaking eiiort including hand engraving and uncertain etching and has been bev 2,179,614 for methods of the so called deep etched lithography, the application ofthis invention to all of these being readily understood by those conversant with the several phases of the art connected therewith. The double printing .of color corrected dry plate negative and line negative on the zinc plates is eliminat'edby the system of the invention because, in stripping the desired portions of one negative to insert in stripped portions of another negative, the edgs of the emulsion are firmly held down with the clear staging solution which prevents their curlingup and this also forms an excellent base over which the opaque staging of the invention may be applied. The so called dry plate negatives have been considered desirable because of the greater fidelity obtainable therewith but have been costly when prepared according to known methods in the past especially because of the large amount of work required thereby and the consequent lack of speed in producing them. The system of the present invention is therefore particularly advantageous when used on dry plates. v

For carrying out the system or method of this invention, there has beenprovided a novel acid and waterproof clear transparent liqu'id'staging solution having controllable quick-drying properties which is usable as such to protect the originally correct and subsequently corrected half tone masses of a negative and which is furthermore adapted to have admixed therewith quarter,

half, and'three-quarter tints of aniline dyes of warm colors such as carmine, scarlet, orange,

' scarlet red, and lustre red, finely powdered aniline dyes .which enable the process artistto at one operation protect the half tone dots and reduce the tonality of the negative to the proper degree of color, either originally or for the purpose of correcting the result of too much etching of the negative. i

At this point it is to be noted that satisfactory staging chemical resist compounds, whether clear transparent,- stained and translucent or opaque must be free flowing from a brush and capable of uniform application in large or small masses, even down to a hair line with the brush.

The results must be free of clouding or spotting and must not crack or show pin holes. In order that the print on paper or zinc may be made without removingthe staging compounds they must not deteriorate when subjected to strong etching acids. The hereinafter described staging compounds have the desired properties which make possible a heretofore impossible rapid and money saving system of color correcting negatives.

For this clear transparent staging solution I employ a liquid Celluloid base and a suitable solvent and thinner. The preferred form of transparent acid resisting liquid staging is made by dissolving Celluloid, e. g., the-finest grade of transparent sheet Celluloid in acetone. The

liquid Celluloid ingredient is made by dissolving water resistingstaging solution when applied to the half tone spot on a negative serves to clarify the dot .by'dissolving a very slight amount of the thin scum or. fringing materials which otherwise produce the penumbra on printing and at the same time renders the mass covered thereby otherwise unchanged except that the dots are definitely and permanently protected against the effects of the etching and other solutions used in correcting negatives.- 5 4 The cleartransparent Celluloid base staging solution is quick drying. Acetone is its solvent and thinner. If a large mass on the negative is to becovered it is sometimes desirable toretard the speed of drying. This is important when stain or dye is mixed with the clear staging as:

' mass by reason of an actual excessive thickness of the staging.

This clear transparent Celluloid base acid resist staging may have a very slight tint of ultramarine or cobalt blue aniline dye added thereto in order to enable the artist to more readily see his work under unsatisfactory'light conditions and without materially altering the tonality of masses staged therewith.

It is also possible to intensify or darken a half tone mass on the negative by applyingselected tints of water stain of aniline dyes of warm colors and then protect this work with a coating of the clear transparent staging solution.

For simultaneously clarifying, intensifying and protecting a half tone spot, I have provided a,

warm-at low heat. The mixture is then cooled and filtered-several times, after which one-twen tieth of a per cent of acetone is added. The resultant mixture is then heated to about a lukewarm temperature and again filtered whereupon one-half part each of amyl acetate and'the dissolved Celluloid is added to the strong stain and kept at ,a mild heat for about five minutes more or less after which the same is allowed to cool and is well shaken. Various lighter tints of this reducing and staging solution can now be produced by the artist who will mix the desired quantity of the aforesaid solution with the clear transparent staging solution aforementioned. The advantages attending the use of the waterproof and acid-proof transparent-stainedstaging solution-will be readily appreciatedby those conversant with the art in view of the foregoing remarks. It is to be noted, however, that in practice the blending of tonalities can be attained and sharp lines between adjacent masses on the negative can be avoided by vignetting the-differently stained masses in the following manner.

The artist applies the desired diiferently stained or the clear and stained, transparent staging solutions to the respective areas but leaves an uncoated margin between them whereupon he' skillfully blends the two masses before they are dry with the aid of a brush dipped in clear transparent Celluloid staging solution. It will be noted that the process of applying the staging solutions partakes of the characteristic of applying color to wash drawings. v

alcohol is slowly added, keeping the mixture n the half tone negatives the white portions of the original drawing, including the usual surrounding border, do not photographon the negative correctly, hence these portions must be opaqued by coating them with a waterproof and chemical resisting opaque staging solution. By

which has acetone for its solvent and the other of which has turpentine for its solvent. As'a further aid to the artist the system also provides a third opaque staging solution which utilizes hot alcohol (denatured) as its solvent. The transparent (clear and stained) stagingchemica resist utilizes acetone for its solvent, hence the turpentine soluble opaque waterproof and chemical resistant staging compound would be'indicated for use adjacent these masses on the negative that have been or are to be staged with clear transparent or stained Celluloid base staging compound. The solvent in each of the saidstaging compounds is ineffective on the other. The third type of opaquing compound is. not

recommended for use any time prior to the finaletching operation.

Since the clear and stained Celluloid base staging solutions as well as the several opaque staging solutions are all relatively quick drying, they do not delay the artist forany appreciable length of time in the correction of his negatives.

The several opaque staging solutions are made substantially according to the following formulas? Celluloid-base opaque solutions I Ounces by weight Clear Celluloid solution (consisting of Celluloid dissolved in acetone and /2 amyl acetate (Merck) 1 I solved are allowed to cool and the twenty ounces 60 of water are added together with three ounces of Free flowing solution of copal gum and acetone 1 Opaque material dry (selected,for contrasting visibility) 8 l The three preferred solution according to this formula utilize 8 ounces of lamp black for black ,Celluloid opaque solution, of 8 ounces of finely.

g jround zinc white for a white colored Celluloid opaque solution, or 2 ounces of said zinc white and 6 ounces of lamp black to make a grey Celluloid opaque solution. In all cases acetone is the thinner and solvent. The quantities of the -'several ingredients may be varied somewhat.

Turpentine soluble opaquing solution or black amber opaque solution N0. 1

Amber (fossil resin) 8 ounces by weight The amber is reduced. to a semi-liquid by heating, after which the boiled linseed oil is added and Gum dammandis sdlvedinhot 25125551111: 3

well mixedtherewith. This is then allowed to become lukewarm, after which turpentine with the gum or gums first dissolved therein is stirred in lamp black is added and mixed therewith.

Turpentine is used as a thinner when needed and as a solvent for removing this opaque medium' I from the negative ifnecessary.

Black amber opaque compound No. 2

This is made substantially like the No. 1 m

formula but omits the gum dammar, and/or gum mastic. l .r Another turpentine soluble opaque "staging compound a volume Lump pitch (heavy street lump tar) melted 2 Lamp black u 1 Japan drierr 1 Turpentine as needed for althinner.

Gum dammar and/or. gum mastic maybe in corporatedup to A the volume.

The heavy pitch is melted to a thick liquid with a little turpentine added. Then-when partly cooled the Japan drier is added. The lamp black is then thoroughly stirred in and enough turpentme is added to provide the desired brushing consistency. Turpentine is usedas a thinner and as a solvent.

All Ofthe foregoing opaque compounds are both 80 water and acid resistant and when applied to a negative form a thoroughly and completely opaque coating that does not crack or show pin holes. The negatives treated therewith remain intact during wide temperature and moisture variations so that no great care, other than guarding against undue scratching, need be exercised in'storlng away thenegatives" for future use and reuse. I

Black waterproofopaque 4i) i Cunces' by weight Shellac (clear or orange) liquid 3 Borax (variable) 1, 2, or 3 Water Gum arabic 3 Lamp black as needed.

The borax and shellac are boiled-and when disum arabic dissolved in warm water., Then the three ounces of gum dammar dissolved'in 'hot' denatured alcohol is added. Lamp black is then added, while stirring, in a quantity suflicient to 66 produce a medium thick liquid. Dissolved gum mastic and/or copal gum are optionally added in this mixture. I

This formula is valuable in many instances and is particularly useful after all etching has been done on the negative. All of the other opaque compounds may be used at any time, i. e., either prior to the first etch for preserving the outline of delicate tone masses that might be lost. on the first etch or at .any other time. The ability to pounds hereinbefore disclosed do not cloud or fog on the negatives nor do they have any inherent tints therein which would detrimentally alter 'printing values of the negative. It has been found that while many apparently clear transparent lacquers and kindred products are avail- 7 Parts by 16 so r quired to be made and corrected for producing a set of color printing plates such as zinc plates. According to the present system, it is to be noted thatone negative is suilicient for each color plate in contradistinction to certain practices now in vogue. It is to be noted also that at no stage during the correction of the negative is it necessary to remove any of the solutions placed on the negative by the artist. Hence a great deal of time and labor is saved. It is further to be noted that the plate maker prints his zinc plates from negatives with all of the artist's work, i. e.,

.all chemical staging resists of clear, tinted or opaque types remaining thereon and, if after proving certain retouching and corrections are necessary, they may be accomplished in practically, every instance without disturbing those masses that are deemed to be correct on proving.

Assuming now for example that the artist has before him the negative or so called yellow plate for a multi-color job. The artist'flrst opaques the bordersection and any masses which in his judgment should show no yellow whatsoever by opaquing over such masses with the amber base or tar base opaque solution which are soluble in turpentine. These masses preferably include masses that are to remain white or are to be printed in color tints which might work out undesirably if printed over yellow. Thus with a few strokes of the brush the artist has on the first stagingoperation definitely and permanently deleted those masses that are to contain no yellow, including those masses that are to contain no color whatsoever. The choice of. opaques affords ample opportunity for the artist to expedite his work and also to save his eyes.

The artist next examines the tonality of the half tone spots with a magnifying glass, com.- paring these masses from time to time with the original painting, color sketch, or the like. The originally applied turpentine soluble opaque or other opaques used are soon .dried and the artist now sele'cts those half tone spots that have in his judgmentphotographed correctly, 1. e., will produce the desired degree of tonality for the-color then under consideration which in this case is yellow. These originally correct masses he brushes over or coats with the clear transparent Celluloid base staging solution and thereby at once clears up the half tone dots and preserves the masses against the action of chemical solutions in the further'preparation of the negative. If .the light conditions under which the artist is working are bccasionally. or characteristicallypoor, the artist is materially aided in seeing the extent of clear transparent staging if a slight tint of ultramarine or cobalt blue aniline dye tint is added to the clear staging solution. This does not affect the light transmitting properties of the staged-mass on the negative. Next those various tone-masses are again carefully scrutinized to determine whether the photographer has overexposed and overdeveloped or whether the nega-- tive is weak by reason of lack of development or by using-poor chemicals or poor developer and also whether the negative is subject to any of the other faults such as underexposure and/or overdevelopment. The process artist must be prepared to correct his half tone negatives'for all of these faults as well as for the mechanical difllculties due to the fact that the normal camera work now obtainable with color filters is but approximately forty per cent correct for tonality and color values. After first staging or coating the initially correct tone masses with transparent Celluloid base staging solution, the artist next selects the half tone masses that appear to-be .too open on the negative and therefore allow too much light to pass through. Over these masses he places a coating of Celluloid base clear staging solution with aniline dye stain therein, selecting or mixing such solutions so as to add a light or heavy quarter tint, light or heavy half tint, or light or heavy three quarter tint to the mass as originally photographed onto the negative. Where blending of tonalities is required to avoid undesired abrupt edges of the masses, the vignetting to the edges of such masses is accom-. plished as heretofore described. After the artist has applied the opaque, clear, and stained chemi-- cal resist staging solutions and in some cases has stained with clear aniline stain-or dye and staged over with clear transparent chemical rsist to eliminate, retain, and modify the color printing values on the negative, he is ready to attend to the etching of various masses that require open-' ing up, i. 'e., to have greater light passing values, by etching to a desired density. For this purpose the artist has left free of staging (1st) all of those masses that are required to be etched to clear glass, and which will represent solid color on the zinc plate, (2d) all masses requiring the photoengravers pin dot, and (3d) all other uncorrected masses that require some degree of additional etching with chemicals to intensify the given color v on the zinc plate.

The next operationis the first etching .operation. According to this system, the etching is desirably carried on in glass trays having strong light shining through from beneath them so that r the artist may observe the progress and rapidity of, the etching with-a magnifying glass without the necessityof frequent removal of the negatives from the solution. The artist is now ready to etch. After a preliminarysoaking of the negative" in water, he places it ina solution of thiosulfate 'of sodium and water and allows it to soak for about three to five minutes. Then putting the negative in a solution of ferricyanide of potassium and water, he studies the gradual etching of those areas that require the slightest amount of etch-- ing. This cutting around the black dots and the white dots are made larger and if allowed to continue its action the "black dots" oh the negative become smaller. When sufli'cient cutting has eventuated for the lightest etch, the same-is placed in a second bath, usually thiosulfate of sodium one ounce, and

, water sixteen ounces, which stops the cutting action of the first bath and clarifies it, i.ge., removes yellow stain that may have been caused by incomplete washing by the photographer when the negative was dried. As soon as the negative has cleared in the thiosulfate of sodium and water solution, it is removed andplaced in a bath of. running water until well washed, whereupon it is allowed to dry, preferably in a placeof uniform temperature and atmospheric condition, if avail-' able. After the first etch has been completed as removes the penumbra from:

20 on successively in very much the same generalaforesaid, the artist now stages over all the corrected tone masses as compared to the same masses of tone on the sketch with clear transparent staging solution or, in the event certain masses have been .etched too much in, the first operation, the clear transparent Celluloid staging has suitable ftints of red aniline dye admixed therewith before application in order to rectify the effects of over-etching. As previously stated, a slight amount of ultramarine blue or cobalt in the staging solution is advisable in lieu of using clear transparent Celluloid staging solution when the masses may be diflicult to see because of poor light conditions. The negative may require one or several more etching operations, particularly when etching to solids or clear glass between which operations the, negative is staged with clear or tinted transparent staging solution on those masses that have been at least sufiiciently etched. These alternate operations are carried order as the photo-engraver etches, stages, and

Then this mass or these masses are againre-etches his heavy zinc or copper plates. The Celluloid base transparent solutions may be termed a permanentliquid transparent chemical resist staging solution capable of color modification for reducing in desired degree the color printing tonality values on the negatives.

It is also understood that retouching with etch solutions or acids, using brushes or wads of cotton rolled on the brush handle or any larger masses may be resorted to for the purpose of eliminating the so-called hard lines between tone masses. This is accomplished by having the negative fairly damp with a solution of thiosulfa'te of sodium and water, and by thereafter swabbing over the mass to be etched with cotton or a brush carrying said thiosulfate of sodium solution and then with another brush or cotton wad carrying ferricyanide of potassium solution, swabbing over the half tone mass and testing the same from time to time with a magnifying glass to determine when the mass is sufficiently etched.

swabbed over with thiosulfate of sodium solution to stop the etching and clarify the mass of half tones, The staging with a Celluloid base transparent staging solution is then effected in a manner hereinbefore described, any excess etching being readily correctible with the transparent Celluloid base staging solution having the dye tints therein.

Thus the process, particularly in massreduction of tonality of the masses of the half tone negative, resolves itself into a series of successive staging with the staging solutions, or chemical resists, etching, staining, and vignetting the various masses of tonality. 1

It is considered de'sirable after staging the negative to place the same in a bath of clear .water for about forty-five seconds,then in a bath of thiosulfate solution for about fifteen seconds,

A great deal of time is saved in these procerses' due to the fact that after the etching step has been completed and the negative has been put I in the thiosulfate of sodium solution to stop the etching, the negative may be placed in a running water bath for about five minutes, removed and partly dried. With the negative still damp,-it is possibleto almost immediately proceed with thenext staging operation, thus carrying on the oper ation bythe required steps of vignetting, etching quarter, or to" clear glass. A vast saving of time is effected because the chemical resist staging solutions, either clear transparent, stained transparent, or opaque, all remain on the negatives so that the plate maker does not have to remove them before making prints on zinc or paper; nor

need any correct work be removed or spoiled in making final corrections and in touching up the negative'after proving same on the proving press.

By reason of the fine degree of control available to the process artist by the use of the system and the novel staging compounds of the invention, it is possible to retain all of the desirable features that are attained, on a dry plate negative, all the features of merit that reside in the plate makers engraving system, in the wet plate or film system, and also deletes substantially all those features that have heretofore caused the so-called dry plate system of process engraving to be so expensive, tedious, and time-consuming.

While the foregoing examples of operations before printing and all chemical resists remain permanently on the negative.

The system of the present invention eliminates the necessity for double printing of negative plates. The difficulties heretofore experienced in stripping work such as type of various sizes on half tone dry plate negatives is completely avoided because the staging solution, either clear, 1

.tinted or stained, or opaque, all serve to literally glue'down the edges which are prone to curl up on one or bothsides and which preclude later applied opaquing from seeping under such edges in a manner well known and highly disagreeable to the'artist'. v I a The method and means of the invention are well adapted to production of the so-called deep etched plates because the chemical resist staging solutions remain on the negative after the deep etched plates are made, thus saving thefully corrected negative for reprints on zinc, if the plates are .ruined on the press.

In projection negative work, e. g., -300 line screen or '175 line small sized screen negative, the usual large amount of crayon artist work is deleted. Likewise, if a plate is spoiled on the press by being gum streaked, it is possible to quickly make another printing plate in a matter.

of an hour or so because the negative is intact as originally corrected and all of the grievous delays and work have been'avoided. As final corrections are frequently required after prov-' ing various negatives, it is not to be overlooked that staining down and blending and vignetting may be put in withwat'er soluble aniline dye and then protected when finally correct with a brush coating of clear Celluloid base staging solution. It willbe apparent to those conversant in the art that with the means and method of the invention making up this system, it is possible to efiect with one set of negatives ai-job that would require the negative-positive-negative system according to previously pursued methods.

' Summarizing the advantages attending the use of the means and method of the present invention, there is to be noted the following. 1. A lesser number of negatives is required to be made for each color actually used than with previous system. 2. The time required to make a given negative is materially reduced because there has been eliminated the heretofore time-wasting operation of removing the chemical resist before each successive operation. 3. Staging compounds of the Celluloid base group permanently save and clarify the half tone mass and, in the case of the tinted solutions, they also reduce it all in one operation. 4. The opaque is also a permanent and protective addition'to the negative. 5.

The character of work obtainable with half tone negatives according to this system enables the artist to produce a multi-color job with a lesser number of negatives, for a lesser number of colors in many instances. This reduction in cost is maniiolded because it also entails fewer negatives,

' fewer corrections, fewer print plates, fewer colors of ink, and fewer press operations.

The method and means of the invention will tend to render more commonly available, because of materially reduced expenses in the production thereof, reproductions having a high degree of fidelity in color tonality.

Reference is made to the drawing which represents schematically and on enlarged scale the character of the factors of the negative, particularly the half tone'masses. Figs. 1. and 2 merely represent schematic enlargements of the penumbral area about the black dot and sometimes greatly limiting the' white dot. Fig. 3 shows an enlarged schematic representation of a black dot and its penumbra. Looking through a half tone mass on' the negative against strong light the characteristic checkerboard design as in Fig. 4 is noted. The black dots l5 and the white dots i6 appear square and connected corner to corner. The same mass viewed in a more subdued light appears as-black and white round dots i1 and 48, respectively, with a light penumbra i9 between them as in Fig. 5.-

. In the connected series of Figs. 6 to 11,- the masses of graduated tonality are shown from a solid to a pin dot. The left hand longitudinal side A-A shows the various tints staged with the transparent staging chemical resist with a V tint of dye in it; thereby holding these different tonalities against the action of etching solutions. The remainder of the continuous series, namely, section 3-3 shows the effect of etching on the unstaged parts of the negative compared with'the parts that were staged before placing the negative-in the: etching solutions.

For example in Fig. 6 A-A is one-fourth tint value while 13-13 has been etchedto enable printing as a light or heavy "engravers pin dot.

Fig. 7 shows at .A-A a heavy quarter tint of tone while B--B shows a similar mass after etching withacids to a tone that may be printed on zinc as either a light or heavy one-fourth tint.

. Fig. 8 shows at A--A a half tone mass and at 3 -3 the same value mass after etching with acids to be printable as a heavy one-half tint or a light three-fourths tint.

Fig. 9 shows at A'A a half tone mass and at B--B the samemass etched with acids to print as a light or heavy three-fourths tint.

I Fig. 10 shows at A-A half tone mass and at BB the same mass etched to be printed as a very heavy three-fourths tint.

- Fig. 11 shows solid black on the negative.

As etching of untreated or unstaged masses is continued the black dots are etched away to progressively smaller size and if continued the dots will be completely etched away to clear glass. Since the permanent staging of transparent Celluloid base solution may be applied to any of the half tone masses that are correct originally or after one or more suitable'etching operations the original imperfect results of cameraphotography can be corrected as to desired mas'ses while others remain unchanged by the etching solutions. Where the negative is not dense enough to produce the desired tonality either due to imperfection of the camera and filter process or due to inadvertent or unavoidable excessive etching with acids the fault is readily correctible by the artist who preferably uses the transparent Celluloid base chemical resist staging solution with the proper tint of aniline dye stain therein but may, where desirable, stain with the proper tint of the aniline dye stain alone and subsequently protect this stained mass satisfactory products for the purposes mentioned and. are to be considered as not strictly limited to the exact details given since they may be I varied within limits without materially sacrifice ing the desired and/or necessary properties which render them useful in carrying out the system of the invention. The keynote of efllciency in the system is the utilization of permanent staging of the several types whereby'the desired masses are retained at correct values without need of removing the staging and the ability to proceed with the correction of the negative rapidly without necessity of any intermediate steps of removing the chemi-' cal resist staging except for correcting definite error on the part of the artist. If such error occurs the rectification is easy and speedy and need never entail the spoilage of negatives. The several solvents for the several staging compounds are ineffective on other adjacent work the zinc press plates are protected against oxidation which occurs frequently on long storage after use, in spite of the gum arabic solution commonly used, by addingv over said gum-arable solution-a coating of my Celluloid base staging solution diluted with a large amount of acetone, e. g.. 16 parts acetone to one part of the solution of V2, amyl acetate and V sheet Celluloid dissolved in acetone. When the press plates are again to'be used the protective Celluloid stagin film is removed by washing with acetone and then the gum arabic coating is washed off with water and the plate is rolled up with ink ready for the press. 1

which comprises coating What isclaimed is:

l. The method of controlled color correction of photomechanical images which comprises the steps of applying, over those'mass tones that are correct, a permanent transparent waterproof and acid-resisting staging compound, etching unstaged tone masses of the image with etching solution until masses requiring the least etching arecorrected, then staging the masses thus corrected with permanent transparent water-' proof, acid-resisting staging compound, repeating the etching and staging operations as required to correct and protect all tone masses of the image, then photographically copying through the corrected image without removing any of the previously applied staging compound.

2. The method of controlled colorcorrection of photomechanical images which comprises staging tone masses of the image that are correct with a waterproof acid-resisting. Celluloid base quick drying liquid chemical resist that forms a transparent permanent protection for such masses, and successively etching with chemicals and staging other masses to effect alterations of the image masses from'a solid to the engravers pin dot as required, then photographically copying through the image without removing the chemical resist. v 3. The method of controlled color correction of photomechanical halftone images which comprises staging tone masses that are correct with a thin; permanent coating of waterproof and acid-resisting transparent staging compound having acetone as its solvent for simultaneously clarifying the dots and protecting said tone masses against chemical etching, and photographically copy ng through the image without removing the staging compound.

4. The method of controlled color correction of photomechanical images-which comprises the,

steps of staging tone masses, requiring intensification witha waterproof, acid-resisting Celluloid base acetone soluble staging solution having a selected tint of known actinic light retarding dye therein to simultaneously clarify and correct the tonality of such masses and protect them against attack by etching chemicals and the deterioratingeflects of atmospheric conditions and then photographically copying through the image without removal ofv the previously applied staging.

5. The method of color. correction of photomechanical images which comprises applying a thin permanent glossy coating of waterproof and chemical-resisting opaque compound to those masses on the image that are to be without colorof photomchanical images which comprises the steps of applying a permanent thin glossy coating of opaque, waterproof, acid-resisting staging compound to image masses from which color solvent whereby said halftone 'taneously clarified and protected'against subselquent chemical etching of unstaged portions of photomechanical image values are to be deleted, then' staging image masses that are correct with clear transparent waterproof, acid-resisting staging compound whereby the several masses are permanently protected, then photographically copying through the corrected image without removing any of the previously applied comp0unds.-

8. The method of controlled color correction of halftone dry plate photomechanical images which comprises the steps'of applying to those masses from which color values are to be deleted a permanent thin glossy coating of opaque, wa-

terproof, acid-resisting staging compound, then staging halftone masses that are correct with a Celluloid base, transparent, waterproof acid-resisting stagingcompound having acetone as its masses are simulthe image and finally photographically copying through the corrected image without removal of any of the previously applied compounds.

9. The method of controlled color correction of photomechanical images which comprises the steps of applying 'a thin permanent coating of dense opaque glossy, turpentine soluble waterproof, acid-resisting opaque staging compound to masses from which all color is to be deleted, then applying to tone masses that are correct a clear transparent waterproofacid-resisting liquid Celluloid staging compound, then applying to those tone masses requiring intensification a'transparent waterproof, acid-resisting Celluloid staging compound having selected tints of actinic light retarding aniline dyes therein, then chemically etching the unstaged masses, arresting the etch-1 ing'from time to time and staging the correctly etched masses with said clear transparent'waterproof, acid-resisting staging compound until all desired masses on the image have been corrected, then photographically copying through the image thus corrected without removal of any of the previously applied staging compounds.

10. The method of controlledcolor correction of photomechanical projection images which comprises the steps of opaquing unwanted image masses with waterproof, acid-resisting glossy.

masses that are correct with a. transparent, waterproof, acid-resisting staging compound, then staging tone masses requiring intensification with transparent waterproof, acid-resisting. staging ,compoundcontaining selected tints of dye of known, light retarding properties, then etching with etching solution the unstaged image masses until masses requiring the least etching arecoropaque staging compound, staging those image rect, staging the masses thus corrected with transparent waterproof and acid-resisting staging compound, repeating the etching and staging:

operations as required on successive. masses,

strlpping .in desired mass tone'image and line image masses where required, securing the edges of such stripped in masses with waterproof, acidresisting staging compound, then photographically copyingthrough the image masses thus corrected by projection onto a sensitized metal printing plate without removing any of said staging compounds, thereby eliminating all crayon work alterations on said metal printing plate.

/ ROBERT L.

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