US2456953A

US2456953A - Photographic reversal processes

Info

Publication number: US2456953A
Application number: US765632A
Authority: US
Inventors: Knott Edward Bowes; Stevens Guy William Willis
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1942-02-09
Filing date: 1947-08-01
Publication date: 1948-12-21
Anticipated expiration: 1965-12-21

Description

Dez; 21, 1948. E. B. KNOTT ET AL 2,456,953

PHOTOGRAPHIC REVERSAL PROCESSES Filed L 1, L947 OBJECT Q) LA YER 0F EMULSION WHICH Z/ FORMS LATENT IMAGE MOSTLY Q INJ/DE SILVER HAL/DE GRAINS EXPOSE 7'0 1. IGHTED OBJECT snow/1 ATQ) AfiOVE LAYER 0F EMULSIONCONTAIN/NG NEGATIVE LATENT IMAGE MOSTLY INS/DZ 77 45 J/LVER HAL IDE GKA/NS SUPPORT TREAT TO FENDER EMULSION C'APABLE 0F FORM/N6 .SURFACf LATENT IMAGE r LAYER 0F EMULSION CONTAINING NEGATIVE LATENT IMAGE MOSTLY INSIDE 771E GRAINS AND C'fIP/IBLE 0F FORM/N6 JURFHCE LATENT IMAGE.

.SUPPDKT F066 ING TREATMENT LA YER or EMULSION caNTA/N/Na NLG'AWVE LATENT IMAGE M0571) INSIDE THE 5/1. VER HAL/DE GRAIN-S AND REVERJED LATENT JUPPORT IOJ/T/VE RECORD or owzcr EDWARD BOW/ES KNOTT GUYWILLMM WILLIS STEVENS INVENTORS gewa.

ATTO EYS Patented Dec. 21, 1948 PHOTOGRAPHIC REVERSAL PROCESSES Edward Bowes Knott and Guy William Willis Stevens, Harrow, Wealdstone, England, assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application August 1, 1947, Serial No. 765,632 In Great Britain February 9, 1942 15 Claims.

This invention relates to photographic processes especially so-called reversal processes.

As is known the latent photographic image formed by the action of light on a photographic silver halide emulsion is not confined to the surface of the silver halide grains but it appears to be also distributed internally throughout those grains. It is possible to develop only the socalled surface latent image by means of developers which have little or no solvent action for silver halide. One of us has described in the literature given below that after removal of the surface latent image the internal latent image can be developed as simply and conveniently as can an ordinary surface latent image if this is done by employing a developer having a solvent action for silver halide; moreover the image so obtained indicated that the s, eed of the emulsion as measured by the internal image is often comparable with the speed as measured by the surface developed image. Such a developer is for convenience called an internal developer, and an example of such a developer is given on page 47 of the Phot. J 1942, 82, 42.

- There is a type of emulsion, which while known per se, is according to our recent investigations of such a nature that the latent image is formed mostly inside the silver halide grains and there is relatively little surface latent image formed. Such emulsions have not found much commercial use, in fact they have for a long time been considered as practically useless. We have now found, however, that after such emulsions have been exposed to form an internal latent image therein, they can subsequently be treated to render them more capable of forming surface latent image upon subsequent exposure, and that the extent of the surface latent image forming capability is greatest where the internal latent image was least and vice versa. An example of such type of emulsion is that known as Burton's emulsion given in Walls Photographic Emulsions, 1929, pp. 52-53. Moreover this type of emulsion may be prepared in other known manners, for instance by taking an ordinary silver bromide or silver iodobromide emulsion containing between 0.5 and 5% silver iodide (based on the total silver halide), and coating it as a layer and then drying, treating it with the following bath:

Potassium bichromate gram 12 Cone. sulphuric acid ccs 12 Water do 1000 The time of treatment must be sufficient to inhibit surface latent image formation as can easily be ascertained by exposing (after washing) and then treating with developers of Formulae I and III, given below. Such an emulsion layer can then be used as it is or may be remelted and coated again as desired.

In the present invention we apply the aforesaid discovery to give a new method of producing reversed photographic images as will be hereinafter described.

Various methods are known for producing a positive image in a silver halide emulsion layer which has been exposed so as to produce a negative latent image. Such reversal methods are employed in both black and white and in colour photography. In the present invention such reversal is obtained by employing the said type of emulsion in which the latent image is formed mostly or entirely internally in the grains; that is to say an emulsion only few or none of whose exposed grains are developable to silver by a developing solution which cannot act as a developer for latent image inside the grainssuch a solution is Formula I (below). Whether an emulsion is of this type for the purpose of this invention can be ascertained by treating it (after exposure) in developers of the kind given in Formulae I, II (a) and II (b) and III below. It is of the type defined if it will develop in those of Formula II (a) or II (b) but will not develop or will develop only slightly in Formula 111 and in Formula I.

The developer formulae above referred to are:

Sum-Ace" DEVELOPER p-Hydroxyphenylglycine grams 10 Sodium carbonate (cryst.) do Water to.. ccs 1000 Development time 4 minutes at 20 C.

FORMULA II (a) "Inrrmmn" Davsnornn Hydroqulnone -l grams 15 N-methyl-p-aminophenol sulphate do 15 Sodium sulphite, anhy do.. 50 Potassium br do 10 Sodium hydroxide do 25 Sodium thiosulphate (cryst.) do 20 Water to cs 1000 Development time 3 minutes at 20 C.

rommnn (b).

INTERNAL" DEVELOPER COMMERCIAL DEVELOPER This is the same as Formula II (b) but omitting the sodium thiosulphate.

Formula II (a) is a more energetic developer than Formu a II (b) so that it usually gives a higher effective speed and a higher contrast than Formula II (b) but is often not so convenient, since it has a higher tendency to aerial oxidation and to give fog.

While in this specification we have described out invention partly in regard to a theory of internal and surface latent images, the correctness or otherwise of such theory, is not essential to the successful working of the invention, it being only necessary to choose the emulsions according to the tests hereinafter given.

The present invention employs the following types of emulsions:

TYPE 1 These are the emulsions which will develop (after exposure) in internal developers of the kind given in at least one of the Formula II (a) and II (b), but will not develop or only slightly develop in Formula III or in Formula I.

(1) Normal range of exposures As measured according to normal photographic testing technique when a test layer of the emulsion is coated on a transparent support, for example glass, and the layer is exposed to an intensity scale, the whole of which is exposed for some fixed time between Amth and 1 second and is developed in the internal developer Formula II (a) the transmitted density obtained at any point along the logmE axis over a density range of 3.0 starting from the threshold of the curve (D=0.1 above fog) should be at least 5 times, and preferably at least times the transmitted density obtained when an identical test layer of the emulsion is developed with the surface developer of Formula I or preferably III, the measurements being made at the corresponding (1. e. same) points on the logmE axis.

As indicated, the best (i. e. preferred) emulsions are those giving the highest density ratios, and the very best (i. e. most preferred) emulsions can be selected with greater certainty by substituting Formula II (b) for II (a).

(2) Small range of exposures *ride and bromide (although very little on silver iodide), it is apparent that when making any of the above measurements on an emulsion to ob- 4 tain, with a high degree of precision information on the amount of surface latent image given by such emulsiomit is important to use Formulal.

The reversal process of the present invention depends upon the fact that the type of emulsion defined above, namely one which upon exposure in the ordinary dry state forms the latent image mostly inside the grains, can be treated so as to render it capable of forming surface latent image on exposure. The treatment depends to some extent upon the particular emulsion. Examples of such treatment are as follows:

(1) All or nearly all emulsions of the type defined can be treated by soaking in any ordinary developing solution such as Formula I or III, employing an organic developing agent and which has little or no solvent action on the silver halide.

(2) In the case of some emulsions of the'type defined which are colour sensitised, the treatment can be with plain water alone.

The efiect of any such treatment or any similar treatment for the same purpose can be ascertained by taking an unexposed layer of the emulsion and merely give it the treatment and then subject it to an image-wise exposure and if this image can be developed in a developer of Formula I or III, the treatment can be employed in performing the present invention.

In the present invention we take emulsions of the type referred to and first expose them imagewise in the ordinary way. This exposure produces an internal latent image. The emulsion is then treated so as to render it capable of forming a surface latent image. It is then given a uniform exposure, or an equiva ent treatment to produce a surface latent image such asby chemical fogging. Then it'is developed in an ordinary I developer for developing surface latent images, whereupon a reversal image is thereby developed. The unused silver salt can then be dissolved out in the usual way.

Hence according to the present invention there is provided the method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a light-sensitive silver halide emulsion of the type herein defined, then without developing the latent image so formed to a visible image treating the exposed emulsion layer to render it capable of forming surface latent image, i. e. latent image developable by the aforesaid developers (III) or (I), and then uniformly fogging the emulsion layer to produce latent image some of which is developable by said developers (III) or (I), and then developing the emulsion layer in a developer which develops the latent image Which is developable by said developers (III) or (I) and gives no more than a negligible deve opment of the negative latent image formed by the original exposure compared with the positive image which is developed.

In uniformly fogging the emulsion layer itmay be subjected directly (i. e. not through a negative or positive image) to an exposure of sufiicient intensity and time to cause a reversed image to I develop by treating it in a developer (e. g. developer III) which will develop surface latent images but not develop or develop only slightly the first formed internal latent image. Said developer may, if desired, be a colour developer. The last mentioned exposure (the reversal exposure) is of course by light to which the emulsion is now sensitive and it is preferably of low intensity. The highest contrast in the reversed image is usually obtained by employing for the first (image forming) exposure an overexposure which can be ascertained by a test or series of tests giving different exposures and development of the latent image in a developer such as Formula II (a) or (b) which gives an unreversed image.

After the development of the reversed image, the unused silver salt can be dissolved out in the I usual way.

The reversal exposure may be adjusted by making tests, so as to give the desired strength of reversed image and to some extent errors in the first image forming exposure can be compensated by so adjusting the reversal exposure.

To obtain the best results when the reversal exposure is made during treatment of the emulsion in a developing solution, it is very important that no appreciable development of the reversed image should occur before the completion of the reversal exposure since such development would cause screening of the emulsion grains where it occurs and would lead to a re-reversal effect or to a reduction of the higher densities. To avoid this, one may employ, for instance, a developing solution which is very dilute or whose pH is so low that the surface developing activity is very small.

Examples. of developing solutions having such a low pH are as follows:

It should be noted that for satisfactory results in performing the present invention the emulsion layer, after receiving the first image-forming exposure, must be well soaked with the developing solution before being given the second exposure to produce the reversed image.

An example of a sensitising dye with which may be employed the plain water treatment given above is 5-[ (2-ethyl-1 (2) -benzoxazolylidene)ethylidene] 3 n heptyl 1 phenyl 2 thichydantoin. This is the dye described in Example 3 of U. S. Patent No. 2,282,116. This dye was used at the rate of 0.25 gram of dye for each amount of silver halide equivalent to 1000 grams of silver nitrate.

An advantage of the method of the present invention of producing reversed images is that such emulsion can be made to have a higher efiective speed combined with a lower graininess in the image than that of any known to us which is made for giving a reversed image upon direct development (such material is exemplified by that described and claimed in British Patent No. 524,087.)

An advantage of the method according to the present invention over known methods in which a reversed image is obtained by developing the first formed image to silver and then removing such silver followed by exposure and redevelopment or fogging redevelopment is that only one development is necessary and for black and white work no silver removal bath is required.

The present method may be applied to various other processes, for example to additive colour processes where a multicoloured screen composed of a very large number of coloured elemental filters (side by side) is superimposed on a sensitive emulsion layer; the emulsion employed is of the type indicated above and is processed in the manner already described for'a reversal black and white silver image.

In performing the present invention, it is sometimes found that in the development where the reversed image is produced, there may be a tendency for some development of the first formed latent image to occur and this gives veiled whites. For instance this is particularly likely to occur when the emulsion is dye-sensitised; to test for this in any particular case, one should first expose the emulsion layer behind a step wedge and develop in an intemal developer (Formula 11) then ascertain therefrom the exposure which gave the maximum density, next overexpose another portion of the emulsion layer (say four times the amount which gave said maximum density) and Potassium ferricyanide gram 1 Potassium br m de do 0.5 Water 0s-- 1000 Such a bath does not seriously affect most sensitising dyes (if present in the emulsion) nor the internal latent image.

The accompanyin drawing is a flow-diagram showing the operation of our process. At B is shown coated on a support a layer of photographic silver halide emulsion which forms latent image mostly inside the silver halide grainsv Upon exposure of this emulsion layer to the lighted object shown at A, a negative latent image of the original object or image is formed mostly inside the silver halide grains as shown at C. Upon treatment of this exposed emulsion layer to render it capable of forming surface latent image, the emulsion still contains the aforesaid negative latent image mostly inside the silver halide grains, but is now capable of forming also surface latent image as shown at D. Upon subjecting this emulsion layer which is now capable of forming surface latent image, to a fogging treatment, a reversed (or positive) latent image is formed mostly on the surface of the silver halide grains as shown at E. Upon development of this emulsion layer which contains the reversed latent image in a developer which is capabie of developing surface latent image and gives no more than a negligible development of the negative latent image formed by the original exposure compared to the positive image which develops, a positive record of the original object or image is obtained as shown at F.

This application is a continuation in part of our copending application Serial No. 528,739, filed March 30, 1944, now-abandoned.

What we claim as our invention and desire to be secured by Letters Patent of the United States is:

1. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion, a test layer of which coated on a transparent support and the layer 7 exposed to a light intensity scale for a fixed time between /100 and 1 second, and development for 3 minutes at 20 C. in the following developer (IIa):

Hydroquinone grams 15 N-methyl-p-aminophenol sulphate do 15 Sodium sulphite, anhydrous do 50 Potassium bromide do 10 Sodium hydroxide do.. 25 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the logioE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 5 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (1) p-Hydroxyphenylglycine grams Sodium carbonate, crystals do 100 Water to cs 1000 the measurements of density being made at the same points on the logmE axis, treating the exposed emulsion layer to render it capable of forming latent image developable by the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Water t ccs 1000 uniformly fogging the emulsion layer to produce latent image some of which is developable by the aforesaid developer I11, and then developing the 40 emulsion layer in a developer which develops the latent image which is developable by said developer (III) and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the posi tive image which is developed.

2. The method of producing a reversed photographic image, which comprises exposing to a -lighted object or image, a layer of a lightsensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between and 1 second and development for 3 minutes at C. in the following developer gives a transmitted density at any point along the logioE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water to ccs 1000 oper (IIb):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do Potassium bromide o 4 Sodium carbonate, crystals do 150 Sodium thiosulphate, crystals d0 20 Water to cs 1000 the measurements of density being made at the same points on the logmE axis, treating the exposed emulsion layer to render it capable of forming latent image developable by the following developer (III) uniformly fogging the emulsion layer to produce latent image some of which is developable by said developer III and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer (III) and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

3 The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between and 1 second and development for 4 minutes at 20 C. in the following develp-Hydroxyphenylglycine grams; 10 Sodium carbonate, crystals do 100 Water to ccs 1000 the measurements of density being made at the same points on the IOgIOE axis, treating the exposed emulsion layer to render it capable of forming latent image developable by the aforesaid developer (I), uniformly fogging the emulsion layer to produce latent image some of which is developable by the aforesaid developer (I) and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer (I) and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

4. The method of producing a reversed photographic image, which 'comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and thelayer exposed to a light intensity scale for a fixed time between /100 and 1 second and development for 4 minutes at 20 C. in the following developer (11b) grams Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the logmE axis over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at

least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (1):

p-Hydroxyphenylglycine grams.... 10 Sodium carbonate, crystals do 100 Water to ccs 1000 development of the negative latent image formed by the original exposure compared with the positive image which is developed.

5. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following developer (IIa) Hydroquinone grams- 15 N-methyl-p-aminophenol snlphate do 15 Sodium sulphite, anhydrous do 50 Potassium bromide do.

Sodium hydroxide d 25 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a. transmitted density at'any point along the logioE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to ccs 1000 the measurements of density being made at the same points on the gl0E axis. treating the exposed emulsion layer to render it capable of forming on exposure to light a latent image developable by the following developer (1) 10 p-Hydroxyphenylglycine grams 0 Sodium carbonate, crystals do 100 Water to ccs 1000 uniformly fogging the emulsion layer to produce latent image some of which is developable by the aforesaid developer (1), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer I and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which develops.

6. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between 1/l00th and 1 second, and development for 3 minutes at 20 C. in the following developer (11a):

Hydroquinone grams 15 N-methyl-p-aminophenol sulphate do 15 Sodium sulphite, anhydrous do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the 10g10E axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for '4 minutes at 20 C. in the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do.. Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to ccs 1000 the measurements of density being made at the same points on the logioE axis, treating the exposed emulsion layer to render it capable of forming an exposure to light a latent image developable by the following developer (I) p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do Water to ccs 1000 uniformly fogging the emulsion layer to produce latent image some of which is developable in the aforesaid developer (1), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer I and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which develops.

7. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between l/100th and 1' second, and development for 4 minutes at 20 C. in the following developer (11b) Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do '90 Potassium bromide", do 4 Sodium carbonate, crystals do 150 Water toos-.. 1000 the measurements of density being made at the same points on the logioE axis, treating the exposed emulsion layer to render it capable of forming on exposure to light a latent image developable by the following developer (I):

p-Hydroxyphenylglycine grams Sodium carbonate, crystalsdo 100 Water to -ccs 1000 uniformly fogging the emulsion layer to produce latent image some of which is developable in the aforesaid developer (I), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer I and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which develops.

8. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer or which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between 1/ 100th and 1 second, and development for 4 minutes at 20 C. in the following developer (11b):

Hydroquinone "grams" 12 N-methyi-p-aminophenol sulphatedo 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals -do.. 150 Sodium thiosulphate, crystals do 20 Water to -ccs.. 1000 gives a transmitted density at anypoint along the iogmE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide; do..- 4 Sodium carbonate, crystals -do 150 Water to ccs.. 1000 the measurements of density being made at the same points on the logioE axis, treating the exposed emulsion layer to render it capable of forming on exposure to light a latent image developable by the following developer (I) p-Hydroxyphenylglyclne -grams 10 Sodium carbonate, crystals do 100 Water to --........ccs== 1909 uniformly fogging the emulsion layer to produce latent image some of which is developable in the aforesaid developer (I), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer I and gives no more than a, negligible development of the negative latent image formed by the original exposure compared with the positive image which develops.

9. The method of producing a reversed photographed image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between 1/100th and 1 second and development for 3 minutes at 20 C. in the following developer (IIa):

Hydroquinone grams 15 N-methyl-p-aminophenol sulphate do 15 Sodium sulphite, anhydrous do Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosuiphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the logmE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (I) p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water to ccs.. 1000 the measurements of density being made at the same points on the logmE axis, soaking the exposed emulsion layer in a photographic developer which develops substantially only the latent image which is developable by the following developer Hydroquinone grams 12 N-methyl-p-aminophenol do 3 Sodium sulphite, crystals do Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to ccs 1000 for a length of.time sufilcient to give no more than a negligible developmentof the latent im. age but sufilcient to render the ermulsion layer capable of forming surface latent image which is developable by the aforesaid developer (III), and then subjecting the emulsion layer to a uniform exposure to light to produce latent image some of which is developable by the aforesaid developer (III), and then developing the emulsion layer in a developer which develops the latent imagewhich is developable by said developer (III) and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

10. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of light-sensitive silver halide emulsion a test layer of which coated on a transparent support and thevlayer exposed to a light intensity scale for a fixed time between 1/ th and 1 second and development 13 for 4 minutes at 20 C. in the following developer (11b):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals ..do 90 Potassium bromide do 4 Sodium carbonate, crystals do- 150 Sodium thiosulphate, crystals do 20 Water to ccs 1000 p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water to os..- 1000 the measurements of density being made at the same points on the logiuE axis, soaking the exposed emulsion layer in a photographic developer which develops substantially only the latent image which is developable by the aforesaid developer (I) for a length of time suflicient to give no more than a negligible development of the latent image but insuflicient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer (I), then subjecting the emulsion layer to a uniform exposure to light to produce latent image some of which is developable in the aforesaid developer (I), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer I and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

11. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between /moth and 1 second and development for 3 mingives a transmitted density at any point along the logioE axis, over a. density range of 3 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III) Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to ccs 1000 the measurements of density being made at the same point on the logroE ,axis, soaking the exl4 posed emulsion layer in a photographic developer which develops substantially only the latent image which is developable by the following developer (I):

p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water to ccs 1000 for a length of time sufilcient to give no more than a negligible development of the latent image but insufficient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer (I), then subjecting the emulsion layer to a uniform exposure to light to produce latent image some of which is developable in the aforesaid developer (I), and then developing the emulsion layer in a developer which develope the latent image which is developable by said developer I and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

12. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image. a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer is exposed to a light intensity scale for a fixed time between /100 and 1 second and development for 4 minutes at 20 C. in the following developer (IIb).:

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do Potassium bromide do 4 Sodium carbonate, crystals do 150 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the iogmE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III):

Hydroquinone -grams l2 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to ccs 1000 the measurements of density being made at the same points on the logloE axis, soaking the exposed emulsion layer in a photographic developer which develops substantiall only the latent image which is developable by the following developer (I):

p-Hydroxyphenylglycine "grams" 10 Sodium carbonate, crystals do Water to ccs 1000 for a-length of time sufficient to give no more than a negligible development of the latent image more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

13. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between /um and 1 second, and development for 4 minutes at C. in the following developer (IIb):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium br do 4 Sodium carbonate, crystals do 150 Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the logioE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog. at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed ior 4 minutes at 20 C. in the following developer (I) p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water to 00s.. 1000 the measurements of density being made at the same points on the logic}? axis, soaking the exposed emulsion layer in the aforesaid photographic developer (I) for a length of time sufficient to give no more than a negligible development of the latent image but sufl'lcient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer I, then subjecting the emulsion layer to a uniform exposure to light to produce.

Hydroquinone "grams-.. 15 N-methyl-p-aminophenol sulphate do.... 15 Sodium sulphite, anhydrous do 50 Potassium bromide do 10 Sodium hydroxide do Sodium thiosulphate, crystals do 20 Water to ccs 1000 gives a transmitted density at any point along the logmE axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do 150 Water1to ccs 1000- the measurements of density being made at the same points on the logmE axis, soaking the exposed emulsion layer in the following photographic developer (I) p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do 100 Water in ccs 1000 for a length of time sumcient to give no more than a negligible development of the latent image but sufficient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer (I), then subjecting the emulsion layer to a uniform exposure to light to produce latent image some of which is developable in the aforesaid developer (1), and then developing the emulsion layer in the aforesaid developer (I).

15. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, a layer of a light-sensitive silver halide emulsion a test layer of which coated on a transparent support and the layer exposed to a light intensity scale for a fixed time between 55 and 1 second and development for 3 minutes in the following developer (IIb) Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3 Sodium sulphite, crystals do 90 Potassium bromide -do i I 4 Sodium carbonate, crystals do 150 Sodium thiosulphate, crystals do 20 Water to cs 1000 gives a transmitted density at any point along the log E axis, over a density range of 3.0 starting from the threshold of the characteristic curve beginning at a density of 0.1 above fog, at least 10 times the transmitted density obtained when an identical test layer of the emulsion is developed for 4 minutes at 20 C. in the following developer (III):

Hydroquinone grams 12 N-methyl-p-aminophenol sulphate do 3v Sodium sulphite, crystals do Potassium bromide do 4 Sodium carbonate, crystals do 150 Water to 00s-- 1000 the measurements of density being made at the same points on the logioE axis, soaking the exposed emulsion layer in the following photographic developer (I) p-Hydroxyphenylglycine grams 10 Sodium carbonate, crystals do- Water to for a length of time sufiicient to give no more than a negligible development of the latent image but sufficient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer (1) then subjecting the emulsion layer to a. uniform exposure to light to produce'latent image some of which is developable in the aforesaid developer (I), and then developing the emulsion layer in the aforesaid developer (I).

EDWARD BOWES KNO'I'I. GUY WILLIAM WILLIS STEVENS.

No references cited.

Certificate of Correction Patent No. 2,456,953. December 21, 1948.

' EDWARD BOWES KN OTT ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 10, line 47 for the word an read on; column 12, line 56, for ermulsion read emulsion; column 13, line 53, for the numeral 5 read 50; line 60, for 3 0 read 3.0; column 14, line 18, for develope read develops; line 28, strike out is before "exposed; column 15, line 50, after layer strike out is; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 3rd day of May, A. D. 1949.

' THOMAS F. MURPHY,

Assistant Oommz'aaz'oner of Patents.