US2100224A - Color photography - Google Patents

Description

' Nov. 23, 193 7.

COLOR PHOTOGRAPHY Filed Feb. 26, 1955 F; H. SNYDER ET AL QfEQMX Gnu/mug Patented Nov. 23, 1937 PATENT OFFICE" 2,100,224 I COLOR rno'rocaarny Francis E. York, N.

Snyder and Henry w. Rimbach, New Y., assignors to Francis H. Snyder,

Inc.,'New York, N. Y., a corporation of Delaware Application February 26, 1935, Serial No. 8,344

2 Claims.

This invention relates to improvements in color photography, and more particularly to a novel method of reproducing prints and transparencies innatural colors.

. We are aware that color photography in vari ous forms has been practiced in recent years, and efforts in this direction have been more or less successful so far as final results are concerned, although the practicing-of the methods involved 1Q has been attended by numerous difiiculties.

Quite recently there has been 'a substantial demand for the reproduction of photographs in color for use in magazine advertising, andsuch demands have been met by the'production of 15 photographs in color produced by several methods.- These methods involve, substantial technical difiiculties which need not be discussed in detail, and the desired results have been secured only at substantial expense.

' A further object is to provide a method of color photography wherein the number of steps involved in the production-of the final picture is substantially reduced and wherein the successive steps of the method may be easily practiced.

A further object is to provide a method of color photography wherein the total time .required for practicing thesuccessive steps of the subject to the production of the finished picture may be carried out in a minimum length of time, and wherein the finished picture represents remarkable fidelity of color to permit the production of extremely attractive pictures.

A further object is to providela method of the character referred to which lends itself equally well to the production of transparencies or prints.

We have discovered that the principles of subtractive color printing may be utilized to advantage in producing a transparency or print in colors which accurately represent the colorsof the subject which have been photographed. In

' 50 the practice of the process, thesubject is photographed three times in as rapid succession as possible, 'a green filter being employed in the first exposure to filter'out the red color component of the subject, a blue fllterbeing emplayed in the second exposure to filter out th':

The present invention has for its principal ob-' I method from the initial photographing of the yellow component, and a red filter being employed in the third exposure to filter out the blue or blue-green component. The three negatives are then developed, fixed and washed in accordance with the usual practice and the portions of the negatives representing the colors filtered out in the three camera exposures will have the silver bromide or other light sensitive material unactivated, which permits of its removal ,in the fixing bath.

The three negatives thus produced are reproduced in positives, thus reversing the light values and causing the positives to appear in black or various tones of darker gray in the portions of the individual films representing the colors in- 1 itially filtered out. In tha production of the positives we preferably employ what is known in the trade as stripping film which comprises apaper backing having successive layers on one side thereof of a soluble gum such as gum arabic, 3 an extremely thin film of celluloid, and a gelatin emulsion of silver bromide or similar light sensitive material. The gum layer of the stripping film is arranged against the paper backing thereof, while the light sensitive emulsion forms the outer layer to be acted upon by a. developing solution;

The three stripping films which have been exposed in contact with the negatives are then developed, fixed and washed in accordance with so the usual practice, and after the stripping'film has remained immersed for from ten to fifteen minutes in the successive baths, the layer of gum arabic dissolves thus freeing the paper backing sheet from the celluloid film. It will be apparent 35 that a projecting enlarger may be used in order that the final picture may be an enlargement of the negatives. V

The three films thusproduced are placed in separate trays or containers and are toned in 40 colors complementary to the corresponding color filters employed in the original camera exposure to thus reproduce the original three colors of the subject. In the toning process, any toning solution may be employed which is transparent and which replaces the reduced silver in the three positive films. In practice, we prefer to employ the toning methodsdisclosed in our copending application Serial No. 8,345, filed February 26, 1935. When the three positive films are thus 0 toned, they will be-respectively blue, red and yellow to represent the three colors of the subject which were filtered out in the original photographing of the object, and the colors will be t a parent and of densities eorrespondingto the I densities of the same colors in the original subject.

The three films are then superimposed, preferably in the manner described below, to provide the finished picture, and the superimposing of the films provides a resulting picture wherein there is remarkable fidelity to the original object cclorings. The superimposing of the positive films may take place on glass, to provide transparencies, or on paper. If the films are superimposed on glass, the latter may be gelatin coated to cause the films to smoothly adhere to the glass, although the films may be directly applied to the glass, in which case the latter must be perfectly clean to prevent the blistering of the film.

When the films are superimposed on paper, a gelatin coated paper is employed. Such paper may be originally coated with plain gelatin, or an ordinary bromide paper may be employed after being treated in a fixing bath to remove, the bromide, and then thoroughly washed. The gelatin, coating, of course, acts solely as an adhesive, as will become apparent. Since the positive films are transparent it makes no substantial difference as to the order in which the films are superimposed, but since the film bearing the red image is slightly denser than the blue film and the latter is slightly denser than the yellow film, the several films are preferably superimposed by firstplacing the red film in position, followedby the blue film and then the yellow film.

In placing the several positive films in position on the paper, or on the glass as the case may be, the red film is first placed in position, gelatin face down, and gentlyv squeegeed to smooth the film on the backing of paper or glass and to thoroughly remove any air bubbles from beneath the film. When'the film is applied to the paper backing, the application of the film takes place with the paper and its gelatin coating. in a wet condition, and the gentle pressure exerted by the squeegee causes the film to be pressed into, the gelatin coating of the paper. The paper is then dried and subsequently treated by the action of a solvent, such as acetone, to dissolve and thus remove the celluloid film, leaving the red image bonded to the gelatin coating of the paper. The paper is then washed and the blue image is applied over and in the same manner as the red .image, care being taken of course, to accurately superimpose the images with respect to each other. The blue film is very gently squeegeed to smooth it out while still leaving a film of water therebeneath to act as a lubricant and thus permit the two images to be accurately registered, whereupon greater squeegee pressure is applied to fix the blue image in position. The celluloid film of the blue image is then dissolved in the same manner as in the preceding case. The yellow image is then applied in the same manner as the blue image,.except that the celluloid film is preferably left in position thereon to act as a protective coating for the images.

The placing of the third film in position in the manner indicated completes the color reproductions, and as stated, the superimposing may take place either on paper or glass depending upon whether 'a print or transparency is desired. The resultant picture will .be an extremely accurate reproduction in color of the original object and it has been found in practice that the high lights and shadows in the resultant picture arelikewise accurate and highly attractive.

As previously stated, the superimposing of the positive image preferablytakes place in the orderof red, blue and yellow. As an alternative method, the red image may be exposed, developed and color toned directly on an. ordinary paper such as bromide paper with the blue andyellow images made on strip film in accordance with the steps referred to above. In such case, it merely is necessary to superimpose the blue image and then the yellow image in the manner previously referred to. If the alternative method is employed, it will be apparent'that the'negative with the red image must be reversed with-respect t0 the blue and yellow negatives, since it will be apparent that the red image will be directly light exposed on the bromide emulsion on the paper, while the superimposing of the other two positive films takes place by reversing them when turning them face down against the emulsion on the paper. Moreover, it has been found in practice that when the alternative method is employed,

there is some tendency for the bromide paper and its emulsion to swell, when wet, to a different extent than the blue and yellow positives. To avoid this, the. paper bearing the red image, after being developed and dried, is treated with aluminum stearate, rubber latex, rosin size or other waterproofing material which prevents excessive swelling when the emulsion is soaked prior to superimposing the remaining pcsitives. Thus the blue and yellow images may be properly superimposed on the red image already appearing on the paper emulsion.

As an alternative method of procedure, the several positive films maybe successively squeegeed in superimposed position on a ferro-type plate in which case the films are preferably applied in the order of yellow, blue and red. This constitutes a reversal of the preferred order of application of the films previously described, and the purpose of this reversal will become apparent. The ferro-type plate is preferably first well waxed to permit the removal of the films from the plate, whereupon the yellow positive is applied against the plate and its celluloid film removed by a solvent in the manner previously described. The yellow film thus left upon the waxed surface of the plate is washed, whereupon the blue film is applied in the same manner and its celluloid backing removed. The red film is then applied in the same manner, after which it is desired to transfer the superimposed films to a sheet of paper. A paper sheet with a gelatin emulsion thereon is employed as in the previous case,'and the sheet is preferably slightly larger than the film. Since the wax previously applied to the 'ferro-type plate will have been removed from the plate outwardly of the edges of the film, such portion of the plate is preferably rewaxed prior to the application of the paper so as to facilitate the ,removal of the latter. The wet paper is applied and squeegeed and when dry the paper with the superimposed films adhering thereto may be stripped from the ferrotype plate. The use of the ferro-type plate in the'manner referred to provides a high gloss on the finished picture.

The practice of the process may be better understood with reference to the accompanying drawing in which Figure 1 is a diagrammatic representation of a camera set-up for photographing illuminated objects,

Figures 2, 3 and 4'are face views of paper positives,

Figures 5, 6 and '7 are similar views of the same positives after being color toned,

Figure 8 is a view of the finished picture,

Figure 9 is an enlarged fragmentary sectional view of a sheet of stripping paper employed'in the practice of the process, and,

Figure 10 is a similar view of the finished picture sheet.

Referring to-Figure 1, the numeral l designates an ordinary camera having a lens mounting II adapted to project an image to a film or plate I2 in the usual manner. The camera is set up to photograph the desired object or objects, shown in the present instance as being three cubes l3, l4 and I5, colored respectively blue, red and yellow. A light source it is indicated for the purpose of illustration as illuminating the objects from an angle with respect to the front faces of the objects so that each object is shown with one face illuminated and two faces in deep shadow, the latter faces being indicated in Figure 1 as being black. A color filter I1 is arranged in front of the lens ll.

Three separate exposures of the objects are taken on three separate negatives, the three exposures being taken su'ccessivelythrough filters i! of colors which are complementary to the colors of the objects l3, l4 and i5. For example, the exposure of the blue object I3 is taken through a red filter, the exposure of the red object l4 through a green filter, and the exposure of the yellow object I! through a blue filter. The three negatives are then developed, fixed and washed in accordance with the usual practice. It will be apparent that the portion of the first negative corresponding to the blue object l3 will be substantially unexposed because of the filtering out of the blue color, and such portion of the first negative will be substantially clear after the development of the negative. Similarly, the finished second negative will have its portion corresponding to the red object i4 substantially clear, and the third finished negative will have a clear portion corresponding'to the yellow object l5.

Positives are then made from the three nega tives in the manner previously described. For example, the positives may be made on stripping film of the cliaracter illustrated in Figure 9 wherein a backing I8 of paper is coated with a layer of water soluble gum such as gum arabic,

- as indicated by the numeral IS. A thin layer of celluloid 20 is applied to the gum layer l9. A layer of light sensitive emulsion 2| is applied over the outer surface of the celluloid layer 20, and this material may be any of the light sensitive emulsions in common use, such as silver bromide.

In making the positives from the three negatives referred to, the particular method employed will depend upon the results desired. as previously stated. For example, if it is desired to make the positives of the same size 'as the negatives, contact prints may be made. If the resulting picture is desired to be an enlargement, a projecting enlarger may be employed in exposing the positives. After thepositives have been exposed in accordance with the desired method, they are developed, fixed and washed inaccordance with the usual methods and the soaking of the strip film in the various baths to which it is subjected causes the gum layer l9 to dissolve, thus freeing the film 2| and emulsion 20 from the paper l8. The three developed positives will then appear as. indicated in Figures 2,3 and 4. As previously stated, the portion of the developed negative corresponding to the blue image l3 will appear substantially clear, and this image will then be developed in the positive to appear relatively dark as indicated by the numeral 22. In a similar manner, the image of the red object I 4 will appear relatively dark in the second positive as indicated by the numeral 23, and the image corresponding to, the

yellow object I5 will appear relatively dark as.

indicated by the numeral 24.

After the development of the positive films in,

the manner referred to, these films are color toned in colors complementary to the colors of the respective filters II employed in the original photographing of the objects, such complementary colors, of course, being the blue, red and yellow of the objects. Thus it will be apparent that the three positive films after being so treated, will be colored to correspond to the objects. in other words, the image 2; would then appear blue as indicated by the numeral 25 in Figure 5, while the images 23 and 24 will then appear red and yellow as indicated respectively by the numerals 26 and 21 in Figures 6 and 7. As previously stated, the color toning is preferably accomplished by the use of suitable toning baths which function to replace the particles of material forming the images with transparent or translucent colors of densities corresponding to the densities of the different portions of the positives as originally developed. In other words, the image 22 will appear relatively dark in the positive-before being toned. and the corresponding image; appears a relatively dark blue as represented in Figure 5,'the density of the color corresponding of course, to the density of the color of the object IS. The same thing ap plies to the images it and 21 in Figures 6 and 7, these images being colored respectively red and yellow in accordance with the colors-of the respective objects I and i5. .While any toning solution may be employed which replaces the particlesof material forming the images with the proper transparent or translucent colors to provide transparent resultant positives. it is preferred that the toning be carried out in accordance with l the disclosure in our copending application Serial No. 8,345, referred to above.

After the positives have been color toned in the manner described, they are thoroughly washed and then kept immersed in a very dilute solu-' tion of acetic acid, preferably a 1% solution, to maintain the films in a firm condition until they are.ready for use in forming the finished picture. When it is desired to superimpose the pictures in the manner referred to; the positive films are re- 'moved from the acetic acid and washed with clear relatively cold water, it being well known that warm water will greatly soften and weaken films of this character. l

The three positive films are then superimposed on a gelatin coated paper in themanner previously described, the red film preferably being applied first, the blue film second, and the yellow film last. This preferred order of application of. the

the true colors show up more clearly and-accurate ly when the films are applied on the order mentioned.

Assuming that the positive films are applied to paper in the the paper in the order mentioned, the red film will be removed from its bath of water and placed on .60 films to the gelatin coated paperis preferably a the paper, emulsion side down, in contact with.

the gelatin coating of the paper, whereupon a squeegee is employed for smoothing the .film on the paper and thoroughly removing any air bub--' bles from beneath the film. The paper is then dried after which it is subjected to the action of a suitable solvent for removing the celluloid film 20, and for this purpose, acetone may be em- :ployed, as will be apparent. The paper is again washed, whereupon the blue positive is applied in the same manner, the emulsion side of the film being applied against the red image on the paper.

The newly applied film and the paper are both in a wet condition, and the film is squeegeed gently to smooth it out with respect to the paper without expelling all of the water from beneath the film. Such layer of water acts as a lubricant to permit the blue film to be moved over the red I image to be properly registered therewith, whereupon the squeegee is again applied to cause the blue film to adhere to the red image and the paper emulsion. The paper is again dried and subjected to the action of the solventreferred to to dissolveand remove the celluloid film.

The paper is then washed to remove the solvent therefrom, whereupon the yellow positive film is applied in the same manner as the blue film, the squeegee being lightly applied to smooth out the yellow film without expelling all of the water from beneath the film whereby it readily may be moved into perfect registration with the previously applied image. The squeegee is more firmly applied after perfect registration of the yellow film is obtained to cause perfect adhesion between the film emulsion and the paper emulsion and the images previously applied thereto. In this connection, attention is invited to the fact that each of the images, as applied and squeegeed will be pressed into the emulsion on the paper to become a part thereof, and after the yellow film has been applied the celluloid film is left in place thereon to form a protective coating for the image. .A finished paper will thus be substantially in the form indicated in Figure 10 and will comprise a paper base 28, a layer of emulsion 29 thereon with the images embeddedin the emulsion, with the celluloid layer 20 of the yellow film left in position to form a protective coating, as previously stated.

The finished print will then appear as indicated in Figure 8 with three images 30, 3| and 32 thereon, and these images will be respectively blue, red and yellow to correspond exactly to the objects.l3, l4 and Hi. The faces of the-images corresponding to the faces of the objects directed toward the camera will show in the clear true colors-of the images. The faces in shadow will appear extremely'dark as in the case of the shadowed faces of the objects. Thus it will be apparent that the present method provides a true reproduction of the object or objects in color.

The practice of the process is much more rapid and accurate than any methods of which we are aware, it being required merely that the operator exercise reasonable care in carrying out the several steps of the process. No substantial amount of skill is necessary, and only a little practice is required to permit the operator to produce consistently accurate pictures. Because of the transparency of the colors of the positive films, there is a perfect blending of the various color components, the appearance of the finished picture to the observer being a remarkably accurate reproduction of the original.

In this connection, the drawing indicates the reproduction of three separate objects of difierent colors. For the purpose of illustration it. will be apparent that objects, persons or scenes involving combined colors will be reproduced with equal accuracy, the various color components being reproduced in the positive films in accordance with their natural density so that the true colors, of whatever nature, will be accurately reproduced in the final picture. The process obviously has wide application for the production of portraits, and the reproduction of any desired ob-'- jects and scenes. For example, the present process is highly desirable for use in producing colored pictures for use in magazine advertisements, these pictures being available at the present time only at excessive cost. Beautiful colorreproductions may be made with the present process .with the entire process carried out infrom 1 to 2 hours at a fraction of the cost of" similar pictures produced in accordance with methods now in use.

As is well known, the majority of photographic reproductions are made on emulsions containing silver halides, the most commonly used photographic paper being the ordinary bromide paper.

Such material produces half-tone prints in variations of black, white and grays. Where the expression half-tone occurs in the claims, however, it is understood that this expression is not limited to black, white and gray reproductions,

but to any other reproductions wherein the'image 1 vention or the scope of the subjoined claims.

We claim:

1. The process of color photography which comprises producing on an emulsion carried by a paper sheet a positive which is in a color representing a reproduction of the tone values of the corresponding color of the subject, producing a plurality of other positives each of which is in a transparent or translucent color different from said first named color and representing a reproduction of the tone values of the corresponding color of the subject, coating the paper sheet with a water proofing material, and successively superimposing and registering such other positives in a wet condition on said first named positive with said emulsion in a wet condition.

2. The process of color photography which comprises exposing an emulsion carried by a paper sheet to produce a positive, developing, fixing, washing and then drying such positive to form a half-tone'image, producing a plurality of other half-tone positives, 'e ach positive hav- FRANCIS H. HENRY w. RIMIBACH.

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