Production of photographic and cinematographic color positives

2,018,196

Oct. 22, 1935. J. E. THORNTON

PRODUCTION OF PHOTOGRAPHIC AND CINEMATOGRAPHIC COLOR POSITIVES Filed May 10, 1934

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inventor

Patented Oct. 22, 1935

2,018,196

UNITED STATES PATENT OFFICE

2,018,196

PRODUCTION OF PHOTOGRAPHIC AND CINEMATOGRAPHIC COLOR POSITIVES

John Edward Thornton, Jersey, Channel Islands

Application May 10, 1934, Serial No. 724,.,98 In Great Britain April 6, 1934

Claims.

This invention relates to a method or process for producing photographic and cinematographic multi-color positive pictures of the subtractive type arid comprising either two or four colors.

One feature of the invention is that these subtractive positives are of full-tone character but are produced from camera-originals or negatives which have Images of colored broken-tone character, such as mosaic, lenticular, prismatic, dif10 fraction, line-screen, or the like. In the following description the term “mosaic” is used for convenience, to include any or all of these different forms of “broken-tone” images, and their different varieties are hereinafter more fully dels scribed in detail.

Another feature is that the positives are made in various forms, for example as photographic color prints mounted upon paper or other reflective opaque backing for viewing by reflected light; upon cellulose or transparent paper for lamp shades and other decorative or advertising transparencies; upon a temporary paper support for use as a transfer to any desired surface; upon glass or cellulose for use as lantern slides for 25 projection; upon cinematograph film for enlarged projection on to a screen; or in any other desired and suitable form for any purpose.

A third feature is that these subtractive positives are of a type and character that are en30 tirely free from light-obstructing silver deposits and will pass a very much greater percentage of light than the mosaic or other originals or any mosaic positive made therefrom by the old orthodox methods of mosaic reproduction.

A fourth feature is that the subtractive positives are made in two parts, as two part-pictures in two sensitized areas upon opposite sides of a thin transparent support, from a negative in which the color parts or color-separations are 40 contained in only one picture area as intermixed colors.

Hitherto mosaic-color paper-prints have been so dull as to be practically valueless, because half the light which should be otherwise reflected back 45 by the white paper support has been blocked out partly by a deposit of metallic silver in the image. But in subtractive paper prints prepared by this invention there is no silver in the image, and therefore 100% of the light is reflected back less 50 the amount absorbed by the opaque support and by the colored colloid forming the image, and for that reason color prints made by this process are clear, transparent, and as brilliant as the regular type of monochrome print.

Subtractive transparencies from mosaic or (Cl. 95—2) other broken tone negatives prepared by this invention upon thicker transparent supports, are as transparent and brilliant as the reflective paper prints aforesaid, because the colored image» contain no silver. g

Subtractive positives made according to this invention are formed in two parts in two layers of gelatino-sllver panchromatic emulsion which is coated upon opposite sides of a transparent cellulose film, each layer being adhered to the 10 support by the usual adhesive substratum. To prevent light projected upon one emulsion during printing from passing through to the other emulsion, a light-obstructing medium Is coated between the two layers of emulsion, as in my 15 Patent No. 1,250,713, or alternatively the two emulsion layers may be stained with a soluble dye that will answer the same purpose. Either kind of light-obstructing medium is washed out during subsequent operations. 20

For mounting as a reflective print on paper or other reflective backing, the positive is made as an extremely thin leaf, almost like tissue, and its cellulose support may be as thin as of an inch or less; also its coloring is very thin 25 and delicate, in order that as much light as possible may pass through and be reflected back from the opaque backing.

For a transparency or a cinematograph film a much thicker cellulose support may be used, 30 such as toot of an inch, or any other thickness according to requirements; also the coloring &amp; more intense than for a reflect-print and the general density of the image is greater for projection. 35

The invention is illustrated in the accompanying drawing in which it is shown applied to the production of a 2-color subtractive positive picture the partial images of which are. formed on opposite sides of a transparent support. In this ⁴⁰drawing:— ^a section through the sensitive mate- rial for making the 2-color subtractive positive of full-tone character from a 2-color negative of broken-tone character. 45 ^{a sec}^^on through the sensitive material after development therein of a pair of black metallic silver Images, and after the application to such images of an ozoplaster which comprises a Porous paper support or backing on to which is 50 coated liquid colloid having the desired coloring matter incorporated therewith.

Mg. 3 is a section through the finished 2-color subtractive positive picture of full-tone charan^ter· 55

2,018,196

The sensitive material for making a 2-color subtractive positive the partial images of which are formed on opposite sides of a transparent support, comprises a transparent support A of 8 cellulose-acetate or other waterproof material which is coated upon both sides with an adhesive x substratum of known type and is then coated upon both sides over the substrata with sensitive gelatino-silver emulsion layers B^l and B²10 preferably of fine grain and panchromatic type. To prevent light projected upon one emulsion during printing from passing through to the other emulsion, a light-obstructing medium is coated between the two layers, as described in 10 my prior Patent No. 1,250,713, or alternatively the two emulsion layers may be stained with a soluble dye for the same purpose. In either case the light-obstructing medium is washed out during subsequent operations.

In producing the 2-color subtractive positive picture from a 2-color (or more than 2-color) camera-original or negative picture (which is color-screened or defined in colors which are complementary to those of the; original scene) 25 the first step is to form upon one of the emulsion layers B^l of double-sensitized film a positive of metallic silver which represents one color-part of the mosaic negative say the red part, and also to form upon the opposite layer B² of the 30 film another positive of metallic silver which represents the other color-part of the mosaic negative, say the green.

This double-sided positive print from one 2color negative is produced by placing the mosaic 35 negative in an optical printing apparatus and projecting two images of the negative on to opposite sides of the positive film, both images being back-to-back, in exact registry one with the other. These two images both alike may be 40 projected and formed by any known optical arrangement. During projection the fine dots or lines of the mosaic image are very slightly spread or enlarged, so that in the image upon the sensitive positive film the dots will practically join up 46 to produce the desired full-tone image. This spreading is effected by any of the various known methods used in spreading mosaic-image dots, for example a ground glass or a lenticular screen is placed between light and negative; or a prism 50 double-image device or an optically plane angularly rotating disc may be interposed in the light beam between negative and positive films, or any other effective known means may be used.

One of the images is projected through a red 55 color-filter C¹ which allows only the red light to pass, and therefore only the red-colored part of the mosaic negative is impressed upon that side of the sensitive film.

The other image is projected through a green 60 color-filter C² which allows only green light to pass, and therefore only the green-colored part of the mosaic negative is impressed upon the opposite side of the sensitive film, back to back against the red-colored part.

The system of optical printing through color filters is somewhat slow, but this is not a serious objection in producing amateur or other photographs where usually only one or a few copies are required.

But when the invention is applied in the production of cinematograph film positives, where the editions required generally comprise many copies of enormous lineal footage and have to be printed quickly, it is convenient to speed up 75 production very greatly by making only one full tone subtractive copy from the mosaic original, and then use this full-tone copy as a printingclichfe from which positive copies can be printed very quickly by the more rapid methods of subtractive color or monochrome printing. The 5 same system of a clichd can also be used for ordinary photographs if large editions are required.

For this purpose the change from broken-tone mosaic images into full-tone subtractive type of images on this printing-clichfe instead of on the 10 final positive print, and In the manner hereinbefore described. It is necessary that the clichfeimage should be made of negative character, this may be ensured in making the clichfe by utilizing either the known method of chemical re- 15 versal, or the known method of hardening the gelatine of the silver image and bleaching and dyeing the non-hardened gelatine.

The exposed and printed film is then developed, thus producing a pair of component-positive 20 images D¹ and D² of subtractive full-tone character and of metallic silver upon opposite sides of the film (see Fig. 2) both of which represent the same tone gradations as those of the original negative. 25

The film may then be fixed, washed and dried, prior to the next operation of coloring. Or if desired such coloring operation may proceed upon the still wet images after development and . washing and before fixing. 30

The next operation is that of bleaching and coloring the subtractive images of metallic silver.

This operation consists in-applying and firmly adhering and uniting to each surface of the gelatin-silver image-layer a layer of colored col- 35 loid, a different color upon each side for each component image, which may be applied by any known means and method.

The preferred method consists in applying what I term an “ozoplaster” E¹, E² to each of the me- 40 tallic silver images. Such ozoplaster consists of a porous paper support or backing cm to which is coated liquid colloid in which the desired coloring matter is incorporated, and which may be a substantially water-insoluble organic dyestuff in 45 a colloidal state of subdivision, or a transparent pigment or mordanted dye, or insoluble dyelake, or other suitable coloring agent, as now used in the preparation of what is commonly known as carbon tissue. As shown in Fig. 2 a green ozo- 50 plaster E¹ is applied to the image D¹ printed through the red filter B¹ and a red ozoplaster E² is applied to the image D² printed through the green filter B². .

Instead of using an ozoplaster the colored 55 colloid may be applied to the image of metallic silver in liquid form, by any of the known methods of coating, brushing, floating, or the like, and is then set or dried.

Various forms of colloid may be used, either 60 alone or mixed, such as gelatine, glue, fish-glue, albumen, gum-arabic, gum tragacanth, agar, or casein. The solvent used for developing the colloid image into relief is therefore chosen according to the colloid selected. For gelatine and glue 65 it will be warm water, and for other colloids cold water or other suitable solvent.

After application of the colored colloid the silver images D¹ and D² are next treated in a bleachhardening solution of well-known type, which 70 usually contain soluble bichromate, ferricyanide, and bromide salts, or in other cases copper salts, or in others chromic acid. Any suitable known formula may be used. The effect of treatment in such a bath is that the silver is bleached and 75

9,018,186 the colored colloid in contact with the silver is rendered insoluble in exact proportion to the amount of silver in the image, and the colored colloid becomes firmly united to the gelatine of 5 the silver image by a process of physical interlocking of the two layers.

The bleached and colored images are then treated in a solvent bath that will dissolve andremove all colloid which still remains soluble and 10 does not form part of the insoluble images. Such bath may be warm or cold water, according to which form of colloid has been used. This converts the colored colloid images into colored relief images F¹ and F as shown in Fig. 3.

The images are also treated in a solvent that will dissolve and remove all salts of silver such as the common “hypo bath” or “ferricyanide and hypo”. This renders the image clear and transparent.

The order of application of the silver solvent and the colloid solvent may be exchanged.

. Finally the images are-washed and dried.

If the colored colloid is of a kind soluble in warm water, such as gelatine or glue, it is neces25 sary that the gelatine layer containing the silver image should be insoluble in such solvent. It is therefore hardened at some suitable stage of manufacture, with chrome alum, formaldehyde, or other hardening agent, and this may be effected 30 during manufacture of the sensitive film or during processing treatment before applying warm water solvent. Or a hardener may be incorporated in the fixing bath, warm water treatment being used later.

ϊ If the colored colloid is of a kind soluble in cold water such as gum-arabic for example, no hardening of the gelatino-silver layer is necessary.

In the foregoing specification red and green j have been used as a simple illustration. But in most 2-color pictures it is preferred to use orangered and blue-green as the complementary pair of colors to produce the most pleasing result. The invention is hot restricted to any particular com5 bination of coloring. In some cases blue-violet and orange might be used.

As wifi be seen from the foregoing description a feature of the invention is that the complementary or inverted colors of the broken tone ti negative are corrected in the subtractive full tone positive by applying each ozoplaster or layer of colored colloid to the opposite side of the negative than the color-record as first formed, and by this means what would otherwise prove wrong 5 coloring in the positive (as compared with the original scene owing to having to print through a positive color-filter of the same color as the inverted color of the negative) is thus corrected and made to rightly correspond to the color of the » original scene.

The picture resulting from the process described will comprise in its first stage two subtractive images of metallic silver D¹ and D² embedded in two lower layers of gelatine B and ' P ^asJ*^{own in Rg}· ² whilst in its final stage (which is shown in Fig. 3) it comprises two subtractive relief images F¹ and F² of insoluble colored colloid in upper layers /1 and /² superimposed upon the lower layers Bi and B² of gelatine from which the original subtractive images of silver have been removed. By this means are formed a subtractive picture with a very high degree of transparency and luminosity, which is free from the light-obstructing agents of the old type of mosaic positive, such as the mosaic color3 filter screen and the filter-blocking mask of black-silver.

The complete positive therefore consists of two partial or component positives of transparent colored colloid alone, in full tone formation, each 5 supported upon a layer of transparent gelatine from which all silver has been removed. Such positive can be utilized in a number of different, ways and for different purposes.

The invention can be extended to produced- 10 color pictures in the same manner by using a pair of mosaic negatives which record four color-separations as described in my Patent No. 1,700,618. The 4-color positive is made by exactly the same procedure as the 2-color hereinbefore described, 15 but the positive film is of doubled area, so that it presents four sensitive picture-areas to the four projected negative images, and four color-filters are used to separate the four colors, so that only one component of the four is printed upon each 20 sensitive surface. The two positive films are then developed as before, and four ozoplasters or four layers of colored colloid are applied, followed by bleach-hardening, relief development, and silver removal as before. After washing and drying 25 the two films are superimposed and cemented together in accurate image registry one with the other, and thus form a complete subtractive full tone picture of four colors.

The colors for a 4-color picture are preferably 30 formed as two complementary pairs, for example, crimson-violet and green, blue-violet and orange; or red, green, blue, yellow, or any other desired combination.

To simplify the procedure only one film mate- 35 rial for the positive and two ozoplasters may be used (as in the 2-color example) by making the positive film-material of double area and the ozoplasters of double area with their differentlycolored areas adjacent to each other. 40

Also the process can be used as part of a 3color picture; the third color, which may be yellow, is formed upon another support such as paper, and the two-color portion is cemented over it, in which case the two colors of the sub- 45 tractive full-tone positive from the mosaic negative would be red and blue and the cemented positive yellow. But other combinations of colors may be substituted such as blue-green and red. ₅₀

The mosaic negatives or printing cliches .The negatives (sometimes known as printing cliches) may be of any known form of brokentone image that record separate analysis of the 55 colors of the original scene or object photographed. The best of these for use with this invention are those known as mosaic negatives.

In its common form this type of negative is generally made with a mosaic filter which gives 60 an analysis of three colors in one picture area, and consists of a transparent support upon which is superimposed a mosaic screen of microscopically small color-filters laid side by side in the same plane and intermingled in close juxtaposition. 65 On this mosaic color-filter is coated a layer of panchromatic sensitive gelatino-silver emulsion of high speed, which is exposed in the camera through the mosaic-filter, then developed, and thus is produced a black mask of silver which 70 defines the image and gradations and blocks out parts of the mosaic filter. The uncovered parts represent the mosaic colored negative, and if the developed image is fixed only, and is not treated by the usual chemical-reversal process 75

3,018,198 (for turning into a positive) its colors are complementary to those of the scene or object photographed.

The preferred form of mosaic-negative for 5 making 2-color full-tone subtractive positives by this invention comprises only two colors. And instead of these two being the strong deep colors which are necessary when the negatives is required to be changed into a positive, the filters 10 are made of specially light and transparent colorings, so that the camera-exposures can be much shorter or more rapid. And, because of the lighter filter-colors, shorter exposures are required in printing from such negatives. The 15 same rule can be followed in making mosaic negatives for producing 4-color mosaic positives.

By departing from orthodox filter-coloring in . the mosaic negative filters in the manner described, very great technical advantages accrue 20 in the processes of reproduction therefrom.

As the mosaic negatives for use in this invention are only fixed, and are not subsequently treated by the usual chemical reversal process, the colors shown in these direct negatives are 25 complementary to the original colors of the scene or object photographed, and it is therefore necessary to correct them by a color-reversal and not a negative-reversal method. In the present invention this is accomplished by 30 applying to each side of the printed positive of silver images an ozoplaster of a color which is the same as that of the original scene or object and is complementary to the color seen in the negative, as hereinbefore described.

For producing 2-color positives any other standard form of mosaic negative may be used, such as the ordinary 3-color mosaic which makes three separate color-analysis, or even a mosaic negative which makes four color-anal40 ysis in the same picture-area of the same negative may be used for producing the 2-color positives. ,..

If the 2-color full-tone subtractive positive made according to this invention is reproduced 45 from such a 3-color or 4-color (mosaic or other color-filtered broken-tone) original negative, then the color scale of the positive represented in only two parts or color-separations will be somewhat wider in each part of the positive than in 50 each part of the negative, because each part of the positive, will reproduce portions of two portions of each negative, whether such negative be of 3-color or 4-color fonn. This method of making a 2-color full-tone subtractive positive from a 55 negative which represents more than two colorseparations therefore has considerable technical advantages. In a further extension of the invention 4-color full-tone subtractive positives are made with four separate color-separations upon 60 four sensitive areas. In one preferred method of doing this a set of 4-color mosaic negatives is used which are made according to Patent 1,700,618, in which the four colors are represented in a doubletiivb pair of negatives which combined comprise 65 an analysis of four colors.

By applying the aforesaid system of increasing the color scale the 4-color full-tone subtractive positives are made with four separate color-separations of a wider range by using a double-three 70 pair of negatives containing an analysis of six colors, which are condensed into four positive images of wider color range.

Modified or alternative forms of negatives ». Another form of broken-tone negative clichA is that known as a lenticular negative. To make subtractive full-tone positives from such lenticular negative it is projected through the same or a similar lens and multi-color filter used in taking the negative, on to the double-sensitized post- 5 tive film, after which procedure is as hereinbefore described.

Other types of broken-tone clichA or negativesystems of color-separation which can be used for projection as colored negative images for 10 making full-tone subtractive color positives according to this invention in conjunction with suitable optical apparatus and color filters, are those known under such various names and types or classes as prismatic, prismatic-dispersion, 15 diffraction, wedge-screen, line-screen, and the like.

State of the art

It is already known to form mosaic dot images upon both sides of a positive film by printing ^acompletely through the film from a mosaic negative applied to one side of the film by alternately covering the negative with differently colored filters. ' . 25

In such cases the positive images have been colored by the application of dyes to each side separate, which is an unsatisfactory method, and incapable of giving the perfect Images attained by the present invention. _M

Silver images formed by printing through are not. suitable for coloring by applied layers of colored Colloid because it could not come in contact with the bases of the silver images and because the colored colloid layer upon the rear side of the support would partially dissolve in the solvent and float off.

Only by projection printing of the primary silver images simultaneously from the same negative upon opposite sides of the support with the bases of such silver image outward, is it possible to make colored colloid images with their bases inwards and points outward, and form bases of new colloid-image-base and in conjunction with a bleach-hardening solution.

On cinematograph film positives it is necessary to add a sound record. This is printed In the margin, as a metallic silver positive, and in the coloring process is treated so that it may remain black-silver, or be made practically colorless, or _Mmay be changed to a colored record, according to the methods described in my concurrent application Serial No. 718,440 filed March 31, 1934.