Photographic bleach accelerators

Abstract

Certain aliphatic thiols, such as diethylaminoethanethiol, are useful as bleach accelerators in processing of photographic elements using aminopolycarboxylic acid bleaching agents, such as the ammonium salt of ferric ethylenediaminetetraacetic acid. The aliphatic thiol can be incorporated in the bleaching bath, or in a bleach-fixing bath which contains a fixing agent such as a thiosulfate in addition to the aminopolycarboxylic acid bleaching agent, or it can be added to a prebath which is used to treat the photographic element after color development and prior to the bleaching or bleach-fixing step.

Description

This invention relates in general to photographic processing and in particular to methods and compositions for the bleaching of photographic silver. More specifically, this invention relates to the use of bleach accelerators for improving the effectiveness of bleaching and bleach-fixing compositions.

In the production of color photographic images it is necessary to remove the silver image which is formed coincident with the dye image. This can be done by oxidizing the silver by means of a suitable oxidizing agent, commonly referred to as a bleaching agent, in the presence of halide ion followed by dissolving the silver halide so formed in a silver halide solvent, commonly referred to as a fixing agent. Alternatively, the bleaching agent and fixing agent can be combined in a bleachfixing solution and the silver removed in one step by use of such solution. A variety of bleaching agents are known for use in photographic processing, for example, ferricyanide bleaching agents and dichromate bleaching agents. It is also well known to use aminopolycarboxylic acid bleaching agents in bleach compositions and in bleach-fix compositions and these agents are preferred from an ecological point of view because they present fewer problems in regard to disposal of waste processing solutions in which they are present. However, the aminopolycarboxylic acid bleaching agents suffer from the disadvantage that they provide a bleaching action which is undesirably slow for use in many photographic processes. It is toward the objective of overcoming this problem by the provision of compounds which function effectively to accelerate the bleaching action of aminopolycarboxylic acid bleaching agents that the present invention is directed.

It has now been discovered that certain aliphatic thiols will effectively accelerate the bleaching action of aminopolycarboxylic acid bleaching agents. The thiol can be incorporated in a bleach bath containing the aminopolycarboxylic acid bleaching agent or in a bleach-fixing bath which contains both the aminopolycarboxylic acid bleaching agent and a fixing agent. Alternatively, the thiol can be incorporated in a prebath which is used to treat the photographic element after color development and prior to the bleaching or bleach-fixing step.

The term "thiol" as employed herein is intended to include precursors which split to form a thiol compound in solution. In carrying out the present invention, the thiol compound can be employed in any amount sufficient to accelerate the bleaching action. It will usually be utilized in the form of a salt, such as an alkali metal or ammonium salt, or the hydrochloride salt, to improve the solubility in the processing solution.

The thiols which are useful for the purposes of this invention are the following:

monothioglycerol,

cystine,

cystamine,

cysteine,

and aminoalkylenethiols of the formula: ##EQU1##

where each of R.sup.1 and R.sup.2 is H, CH.sub.3 or C.sub.2 H.sub.5 and n is an integer having a value of from 1 to 3.

Illustrative examples of aminoalkylenethiols of the formula given above are the following:

2-aminoethanethiol

3-aminopropanethiol

dimethylaminoethanethiol

dimethylaminopropanethiol

N-methyl-N-ethyl-aminoethanethiol

and diethylaminoethanethiol.

The aminopolycarboxylic acid bleaching agents which are used as components of the bleaching compositions and bleach-fixing compositions of this invention are well known bleaching agents. They are typically utilized in the form of water-soluble salts, such as ammonium or alkali metal salts, of a ferric aminopolycarboxylic acid complex. A typical example is the ammonium salt of ferric ethylenediaminetetraacetic acid (NH.sub.4 FeEDTA), which is also known as ammonium ethylenedinitrilotetraacetato ferrate (III). Many other aminopolycarboxylic acids in addition to ethylenediamine tetraacetic acid are also useful such as, for example:

nitrilotriacetic acid,

diethylenetriamine pentaacetic acid,

ortho-diamine cyclohexane tetraacetic acid,

ethylene glycol bis(aminoethyl) ether) tetraacetic acid,

diaminopropanol tetraacetic acid,

N-(2-hydroxyethyl)ethylenediamine triacetic acid,

ethyliminodipropionic acid, and the like. The aminopolyacetic acids are preferred as they are readily available and provide particularly good bleaching action.

The bleach compositions of this invention will generally contain about 5 to about 400 grams per liter of the aminopolycarboxylic acid bleaching agent and more preferably about 10 to about 200 grams per liter. The bleach-fix compositions contain a fixing agent, such as a water-soluble thiosulfate fixing agent, in addition to the aminopolycarboxylic acid bleaching agent. As is well known, thiosulfates which are useful as fixing agents include ammonium thiosulfate and alkali metal thiosulfates such as sodium thiosulfate and potassium thiosulfate. Generally, the bleach-fixing compositions will contain about 5 to about 400 grams, and more preferably about 10 to about 200 grams, of the aminopolycarboxylic acid bleaching agent per liter of solution and about 5 to about 400 grams, and more preferably about 10 to about 200 grams, of the fixing agent per liter of solution. The bleach or bleach-fix compositions can contain other addenda known to the art to be useful in such formulations, such as amines, sulfites, mercaptotriazoles, alkali metal bromides, alkali metal iodides and the like. An additional silver halide solvent such as a watersoluble thiocyanate, e.g., ammonium thiocyanate, sodium thiocyanate or potassium thiocyanate, can be included in the bleach-fix compositions if desired. The bleach-fix composition can also contain a non-chelated salt of an aminopolycarboxylic acid, e.g., sodium salts of ethylenediaminetetraacetic acid, in addition to the ferric salt.

The thiol or salt of the thiol, can be employed in accordance with this invention in any bleach-accelerating amount. When it is incorporated in the bleach or bleach-fixing bath it is generally employed in an amount of from about 0.1 to about 20 grams per liter and more preferably from about 0.5 to about 5 grams per liter. When it is employed in a prebath for treating the photographic element after color development and prior to bleaching or bleach-fixing it can also be utilized in these same amounts. The prebath can be simply an aqueous solution of the thiol or it can additionally contain other addenda such as sulfites, alkali metal iodides, and buffer salts. As previously indicated, the thiol can be used in salt form to provide improved solubility in the prebath, bleach bath, or bleach-fix bath. Also, the thiol may be provided in the form of a precursor, such as cystine, which splits to yield a thiol when dissolved in the processing bath.

The bleach accelerators described herein can be used in the processing of photographic elements designed for reversal color processing or in the processing of negative color elements or color print materials. They can be employed with photographic elements which are processed in color developers containing couplers or with photographic elements which contain the coupler in the silver halide emulsion layers or in layers contiguous thereto. The photosensitive layers present in the photographic elements processed according to the method of this invention can contain any of the conventional silver halides as the photosensitive material, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide, and mixtures thereof. These layers can contain conventional addenda and be coated on any of the photographic supports, such as, for example, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polycarbonate film, polystyrene film, polyethylene terephthalate film, paper, polymer-coated paper, and the like.

The bleach accelerators of this invention are especially useful in that they provide substantial improvement in bleaching activity without causing undesirable fog formation. Also, while many of the five-membered heterocyclic ring thiols which are known to be bleach accelerators lose most of their activity if iodide ion is present in the bleach-fix solution or the prebath this is not the case with the aliphatic thiols described herein. Since it is often desirable to include iodides in such processing baths to avoid stain formation in the photographic element or to act as "grain scrubbers," this is an important advantage. The ability of the aliphatic thiols described herein to accelerate bleaching is surprising considering the fact that certain aminoalkylenethiols, which differ from those described herein in that the nitrogen atom is substituted with a cycloalkane group or alkyl group of at least three carbon atoms, function as bleach inhibitors as described in U.S. Pat. application Ser. No. 201,150 filed Nov. 22, 1971 and issued July 31, 1973, as U.S. Pat. No. 3,749,572. A further advantageous feature of the aliphatic thiols described herein is that they improve the ability of the bleaching agent to effect complete removal of all of the silver from the photographic element, whereas without the use of these thiols it is often very difficult to remove the last traces of silver even with prolonged bleaching times.

The invention is further illustrated by the following examples of its practice.

EXAMPLE I

A multilayer color negative photographic motion picture film (Eastman Color Internegative Film, Type 5271) was sensitometrically exposed and processed in the following sequence, in which all processing steps were performed at 75.degree.F:

Processing Bath Time ______________________________________ Prebath 15 sec. Wash 15 sec. Color Developer 9 min. Stop-fix 2 min. Wash 2 min. Bleach-fix 2 min. Wash 5 min. Stabilizer 1 min. ______________________________________

The compositions of the prebath, color developer, stop-fix, bleach-fix and stabilizer were as follows:

Prebath Water 800 ml. Borax (Na.sub.2 B.sub.4 O.sub.7 .sup.. 10H.sub.2 O) 20.0 g. Sodium sulfate, desiccated 100.0 g. Sodium hydroxide (10% solution) 10.0 ml. Water to 1 liter (pH 9.30) Color Developer Water 800 ml. Sodium hexametaphosphate 2.0 g. Sodium sulfite, desiccated 4.0 g. 2-amino-5-diethylaminotoluene monohydro- chloride 3.0 g. Sodium carbonate, monohydrated 20.0 g. Potassium bromide 2.0 g. Water to 1 liter (pH 10.65) Stop-Fix Water 600 ml. Sodium thiosulfate 240.0 g. Sodium sulfite, desiccated 15.0 g. Acetic acid 13.4 ml. Boric acid 7.5 g. Potassium alum 15.0 g. Water to 1 liter (pH 4.25) Bleach-fix Water 800 ml. Hydrochloric acid (concentrated) 9.2 ml. Sodium sulfite 12.0 g. NH.sub.4 FeEDTA (1.1 molar solution) 92.0 ml. Ammonium thiosulfate (60% solution) 200.0 ml. Water to 1 liter (pH 6.5) Stabilizer Formaldehyde (37% by weight solution) 15 ml. *Wetting agent 2 ml. Water to 1 liter *A mixture of a nonionic surfactant and an alkyleneglycol in water as described in Column 5 of Hanson et al, United States Pat. No. 3,246,987.

The amount of silver left in the film after completion of the processing sequence was determined by infrared (900 nm.) densitometry. The infrared density of D.sub.max exposure was found to be 0.90 with a bleach-fixing time of 2 minutes. Increasing the bleach-fixing time to 4 minutes reduced the infrared density to 0.50 while increasing the bleach-fixing time to 8 minutes reduced the infrared density of 0.30. By comparison, when a sample of the same film was processed under identical conditions except that diethylaminoethanethiol hydrochloride was included in the bleach-fix at a concentration of 0.5 grams per liter of solution the infrared density was 0.07 for 2 minutes of bleach-fixing, 0.06 for 8 minutes and 0.06 for 8 minutes.

EXAMPLES 2 to 5

Four different bleach accelerators of the present invention were tested in the same manner described in Example 1 using the same film and processing solutions. The infrared densities were determined in each of these tests for bleachfixing times of 2, 4, and 8 minutes. The amount of the bleach accelerator included in the bleach-fixing composition and the infrared densities obtained are reported in the following table:

Concentration of Bleach Accelerator Infrared Density Bleach Accelerator in Bleach-Fix Solution 2 min. 4 min. 8 min. __________________________________________________________________________ 2-aminoethanethiol hydrochloride 0.5 g. per liter 0.06 0.06 0.06 monothioglycerol 1.0 ml. per liter 0.06 0.06 0.06 L-(+)-cysteine hydrochloride 0.5 g. per liter 0.63 0.11 0.06 L-(-)-cystine 0.5 g. per liter 0.74 0.23 0.06 __________________________________________________________________________

EXAMPLES 6 to 9

A multilayer color negative photographic motion picture color film substantially the same as the film utilized in Examples 1 to 5 except that it was a forehardened film modified in sensitometry for 100.degree.F processing was sensitometrically exposed and processed in the following sequence, in which all processing steps were performed at 100.degree.F.

______________________________________ Processing Bath Time ______________________________________ Prebath 10 sec. Wash 10 sec. Color Developer 2 min. Stop 1 min. Wash 40 sec. Fix 1 min. Bleach-fix 80 sec. Wash 1 min. Stabilizer 10 sec. ______________________________________

The compositions of the prebath, color developer, bleach-fix and stabilizer were the same as those of Example 1. The stop bath was an aqueous solution having a pH of 3.1 and containing 6.5 grams per liter of sodium bisulfite and 24.5 milliliters per liter of glacial acetic acid, while the fix bath was an aqueous solution having a pH of 6.7 and containing 13 grams per liter of sodium sulfite, 7 grams per liter of sodium bisulfite and 200 milliliters per liter of a 60 per cent solution of ammonium thiosulfate.

Film samples were tested with no bleach accelerator in the bleach-fix solution and with each of five different bleach accelerators of the present invention in the bleach-fix solution and in each instance the amount of silver left in the film after completion of the processing sequence was determined in the same manner as described in Example 1. The amount of bleach-accelerator included in the bleach-fix solution and the infrared densities obtained are reported in the following table:

Concentration of Bleach Accelerator in Bleach-Fix Infrared Bleach Accelerator Solution Density ______________________________________ None -- 0.56 monothioglycerol 1.0 ml. per liter 0.06 cystamine dihydrochloride 0.5 g. per liter 0.06 dimethylaminopropanethiol hydrochloride 0.5 g. per liter 0.06 ammonium thioglycolate 0.5 g. per liter 0.18 ______________________________________

In contrast with the results shown above, when diisopropylaminoethanethiol hydrochloride was added to the bleach-fix solution at a concentration of 0.5 grams per liter the infrared density was 0.86, thereby indicating that diisopropylaminoethanethiol hydrochloride is a bleach inhibitor rather than a bleach accelerator.

EXAMPLE 10

The same film described in Example 1 was processed in the same 75.degree.F process using the identical processing solutions except that the bleach-fix solution contained 0.5 grams per liter of diethylaminoethanethiol hydrochloride and one gram per liter of potassium iodide and the bleach-fixing time was 4 minutes. The infrared density obtained was 0.06 as compared with 0.50 in the control test in which no diethylaminoethanethiol hydrochloride or potassium iodide were included in the bleach-fix.

EXAMPLE 11

A multilayer color reversal photographic motion picture film (Eastman Ektachrome R Print Film, Type 5389) was sensitometrically exposed and processed at 85.degree.F in the following standard process:

Processing Bath Time ______________________________________ Prehardener 3 min. Neutralizer 1 min. First Developer 6 min. First Stop Bath 2 min. Wash 4 min. Color Developer 15 min. Second Stop Bath 3 min. Wash 3 min. Bleach 5 min. Fix 6 min. Wash 6 min. Stabilizer 1 min. ______________________________________

The compositions of the processing baths were as follows:

Prehardener Water 800 ml. Glycine 1.0 g. Succinaldehyde bis-sodium bisulfite 11.0 g. Sodium sulfate, dessicated 147.0 g. Sodium bromide, anhydrous 2.0 g. Sodium acetate, anhydrous 15.0 g. Formalin (37% formaldehyde solution) 27.0 ml. Glacial acetic acid 5.0 ml. Water to one liter (pH 4.8) Neutralizer Water 800 ml. Hydroxylamine Sulfate 18.0 g. Sodium bromide, anhydrous 17.0 g. Glacial acetic acid 10.0 ml. Sodium hydroxide 6.8 g. Sodium sulfate, anhydrous 50.0 g. Water to one liter (pH 5.1) First Developer Water 800 ml. Sodium tetraphosphate 2.0 g. p-Methylaminophenol sulfate 5.0 g. Sodium sulfite, anhydrous 39.0 g. Hydroquinone 5.9 g. Sodium carbonate, anhydrous 24.0 g. Sodium thiocyanate 1.3 g. Sodium bromide, anhydrous 1.5 g. Potassium iodide (0.1% solution in water) 9.0 ml. Water to one liter (pH 9.9) First Stop Bath Water 800 ml. Glacial acetic acid 30.0 ml. Sodium hydroxide 1.75 g. Water to one liter (pH 3.6) Color Developer Water 800 ml. Sodium tetraphosphate 5.0 g. Benzyl alcohol 3.1 ml. Sodium sulfate, anhydrous 7.6 g. Trisodium phosphate .sup.. 12H.sub.2 O 36.0 g. Sodium bromide, anhydrous 0.8 g. Potassium iodide (0.1% solution in water) 28.0 ml. Sodium hydroxide 2.05 g. Citrazinic acid 1.35 g. *Color Developing Agent 10.5 g. Ethylenediamine 3.0 g. Teriarybutylamine borane 0.07 g. Water to one liter (pH 11.25) Tertiarybutylamine *4-Amino-N-ethyl-N-(.beta.-methanesulfonamidoethyl)-m-t oluidine sesquisulfate monohydrate Second Stop Bath Water 800 ml. Glacial acetic acid 30.0 ml. Sodium hydroxide 1.75 g. Water to one liter (pH 3.6) Bleach Water 800 ml. Potassium ferricyanide 90.0 g. Sodium bromide, anhydrous 22.5 g. Disodium phosphate, anhydrous 19.5 g. Monosodium phosphate, monohydrate 7.5 g. Sodium thiocyanate 7.5 g. Water to one liter (pH 6.8) Fix Water 800 ml. Sodium thiosulfate, anhydrous 94.5 g. Sodium bisulfite, anhydrous 17.6 g. Disodium phosphate, anhydrous 15.0 g. Sodium EDTA 0.5 g. Water to one liter (pH 5.9) Stabilizer Water 800 ml. Polyethoxyethanol 0.14 ml. Formalin (37% formaldehyde solution) 6.0 ml. Water to one liter

A second portion of the film was processed using the same process except that the composition of the bleach was as follows:

Ammonium bromide 300 g. Ferric ammonium EDTA (1.56 molar solution) 300 ml. Hydrobromic acid to pH of 6 Water to one liter

A third portion of the film was processed using the same ferric ammonium EDTA bleach described above but modifying the process by eliminating the second stop bath and using a prebath containing a bleach accelerator of the invention immediately prior to the bleaching step. The film was maintained in the prebath for 3 minutes at a temperature of 100.degree.F and the composition of the prebath was as follows:

Sodium carbonate 20 g. L-(+)-cysteine hydrochloride 6 g. Water to one liter (pH 9.0)

The action of the prebath in increasing the extent to which silver is removed from the film is shown by the following differences in silver densities for the film processed with and without the prebath relative to the film processed in the standard process:

Difference in Silver Density Without Prebath With Prebath ______________________________________ At D-Max -0.01 -0.04 At shoulder +0.01 -0.04 At exposure rating +0.05 0 At D-Min +0.02 0 ______________________________________

The effectiveness of the prebath in promoting removal of all silver from the film is also shown by the following values for the difference in dye densities at D-Min for the film processed with and without the prebath relative to the film processed in the standard process:

Without Prebath With Prebath ______________________________________ Red 0.03 0 Green 0.03 0 Blue 0.03 0 ______________________________________

EXAMPLE 12

A multilayer color reversal photographic motion picture film (Eastman Ektachrome R Print Film, Type 5389) was sensitometrically exposed and processed in the following standard process:

Processing Bath Temperature (.degree.F) Time ______________________________________ Prehardener 95 2 min., 35 sec. Neutralizer 95 30 sec. First Developer 98 3 min., 10 sec. First Stop 95 30 sec. Wash 100 1 min. Color Developer 110 3 min., 35 sec. Second Stop 95 30 sec. Wash 100 1 min. Bleach 95 1 min., 30 sec. Fix 95 1 min., 30 sec. Wash 100 1 min. Stabilizer 95 30 sec. ______________________________________

The compositions of the processing baths were as follows:

Prehardener Water 800.0 ml. Sodium p-toluenesulfinate 1.0 g. Glacial acetic acid 2.0 ml. Succinaldehyde bis-sodium bisulfite 8.5 g. Sodium sulfate, anhydrous 75.0 g. Magnesium sulfate, heptahydrate 257.0 g. Sodium bromide, anhydrous 2.0 g. Sodium acetate, anhydrous 15.0 g. Formalin (37% formaldehyde solution) 27.0 ml. 3-Methylbenzothiazolium p-toluenesulfonate 0.04 g. Water to one liter (pH 4.8) Neutralizer Water 800.0 ml. Hydroxylamine sulfate 18.0 g. Sodium bromide, anhydrous 17.0 g. Glacial acetic acid 10.0 ml. Sodium hydroxide 6.8 g. Sodium sulfate, anhydrous 50.0 g Water to one liter (pH 5.1) First Developer Water 800.0 ml. Sodium tetraphosphate 2.0 g. Sodium bisulfite, anhydrous 8.0 g. 1-Phenyl-3-pyrazolidone 0.35 g. Sodium sulfite, anhydrous 37.0 g. Hydroquinone 5.5 g. Sodium carbonate, anhydrous 28.2 g. Sodium thiocyanate 1.38 g. Sodium bromide, anhydrous 1.30 g. Potassium iodide (0.1% solution in water) 13.0 ml. Water to one liter (pH 9.9) First and Second Stop Baths Water 800.0 ml. Glacial acetic acid 30.0 ml. Sodium hydroxide 1.65 g. Water to one liter (pH 3.5) Color Developer Water 800.0 ml. Sodium tetraphosphate 5.0 g. Benzyl alcohol 4.5 ml. Sodium sulfite, anhydrous 7.5 g. Trisodium phosphate .sup.. 12 H.sub.2 O 36.0 g. Sodium bromide, anhydrous 0.9 g. Potassium iodide (0.1% solution in water) 90.0 ml. Sodium hydroxide 3.25 g. Citrazinic acid 1.5 g. *Color developing agent 11.0 g. Ethylenediamine 3.0 g. Tertiarybutylamine borane 0.07 g. Water to one liter (pH 11.65) *4-Amino-N-ethyl-N-(.beta.-methanesulfonamidoethyl)-m-toluidine sesquisulfate monohydrate? Bleach Water 800.0 ml. Potassium ferricyanide 165.0 g. Sodium bromide, anhydrous 43.0 g. Na.sub.2 B.sub.4 O.sub.7.sup.. 5H.sub.2 O 1.0 g. Polyethylene glycol 3.6 g. Water to one liter (pH 8.7) Fix Water 800.0 ml. Sodium thiosulfate, pentahydrate 200.0 g. Sodium sulfite, anhydrous 10.0 g. Sodium EDTA 0.5 g. Disodium phosphate, anhydrous 15.0 g. Water to one liter (pH 8.2) Stabilizer Water 800.0 ml. Polyethoxyethanol 0.14 ml. Formalin (37% formaldehyde solution) 6.0 ml. Water to one liter

Six tests were carried out with the film to determine the effectiveness as a bleach accelerator of a prebath containing an aliphatic thiol as described herein. In each of the tests the film was processed in the processing sequence described above except that the film was bleached for 1 minute and 30 seconds in a bleach bath of the following composition:

Ammonium bromide 300 g. Ferric ammonium EDTA (1.56 molar solution) 300 ml. Hydrobromic acid to pH of 6 Water to one liter

In test number one no prebath was utilized, while in each of tests two through six the second stop bath was eliminated and the film was treated with a prebath for 3 minutes at 100.degree.F immediately prior to the bleaching step. The compositions of the prebaths employed were as follows:

Test No. Composition of Prebath ______________________________________ 1 None 2 L-(+)-cysteine hydrochloride 1 g. Water to one liter (pH 2.6) 3 L-(+)-cysteine hydrochloride 4 g. Water to one liter (pH 2.32) 4 Sodium carbonate 10 g. L-(+)-cysteine hydrochloride 1 g. Water to one liter (pH 9.85) 5 Sodium carbonate 10 g. L-(+)-cysteine hydrochloride 4 g. Water to one liter (pH 8.07) 6 Sodium acetate 3 g. L-(+)-cysteine hydrochloride 4 g. Water to one liter (pH 4.93) ______________________________________

The differences between the silver densities obtained and those obtained with the standard process are as follows:

Difference Test Number in Silver Density 1 2 3 4 5 6 ______________________________________ At D-Max 0.42 0.01 0.00 0.44 0.01 0.00 At shoulder 0.56 0.00 0.00 0.49 0.14 0.09 At exposure rating 0.56 0.01 0.00 0.48 0.11 0.18 At D-Min 0.65 0.03 0.00 0.28 0.00 0.05 ______________________________________

As is shown by the above data, the prebath containing a bleach accelerator of the present invention greatly accelerates the bleaching action and is most effective at low pH values.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

What is claimed is:

1. An improved method of photographic processing in which an imagewise exposed and color developed photographic element is contacted with a ferric aminopolycarboxylic acid complex which functions as a bleaching agent to oxidize photographic silver and with a thiosulfate which functions as a fixing agent, wherein the improvement comprises contacting said element, subsequent to color development and prior to or simultaneously with the contact with said bleaching agent, with a bleach-accelerating amount of a thiol or a salt thereof, said thiol being selected from the group consisting of

monothioglycerol,

cystine,

cystamine,

cysteine,

and aminoalkylenethiols of the formula: ##EQU2## wherein each of R.sup.1 and R.sup.2 is H, CH.sub.3 or C.sub.2 H.sub.5 and n is an integer having a value of from 1 to 3.

2. The method as claimed in claim 1 wherein said bleaching agent is a ferric aminopolyacetic acid complex.

3. The method as claimed in claim 1 wherein said bleaching agent is a water-soluble salt of ferric ethylenediaminetetraacetic acid.

4. The method as claimed in claim 1 wherein said bleaching agent is the ammonium salt of ferric ethylenediaminetetraacetic acid.

5. The method as claimed in claim 1 wherein said thiol is diethylaminoethanethiol.

6. An improved method of photographic processing in which an imagewise exposed and color developed photographic element is contacted with a ferric aminopolycarboxylic acid complex which functions as a bleaching agent to oxidize photographic silver, wherein the improvement comprises contacting said element, after color development and prior to contact with a bleach bath containing said ferric aminopolycarboxylic acid complex, with a bath containing a bleach-accelerating amount of a thiol or a salt thereof, said thiol being selected from the group consisting of

monothioglycerol,

cystine,

cystamine,

cysteine,

and aminoalkylenethiols of the formula: ##EQU3## wherein each of R.sup.1 and R.sup.2 is H, CH.sub.3 or C.sub.2 H.sub.5 and n is an integer having a value of from 1 to 3.

7. The method as claimed in claim 1 wherein said photographic element is contacted with a bath containing said thiol or salt thereof after color development and prior to contact with a bleach-fixing bath containing said ferric aminopolycarboxylic acid complex and a thiosulfate fixing agent.

8. The method as claimed in claim 1 wherein said photographic element is bleached in a bleach bath containing said ferric aminopolycarboxylic acid complex and said thiol or salt thereof.

9. The method as claimed in claim 1 wherein said photographic element is bleach-fixed in a bleach-fix bath containing said ferric aminopolycarboxylic acid complex, a thiosulfate fixing agent, and said thiol or salt thereof.

10. A photographic bleach-fixing composition containing a thiosulfate fixing agent, a ferric aminopolycarboxylic acid complex which functions as a bleaching agent to oxidize photographic silver, and a bleach-accelerating amount of a thiol or a salt thereof, said thiol being selected from the group consisting of

monothioglycerol,

cystine,

cystamine,

cysteine,

and aminoalkylenethiols of the formula: ##EQU4## where each of R.sup.1 and R.sup.2 is H, CH.sub.3 or C.sub.2 H.sub.5 and n is an integer having a value of from 1 to 3.

11. A photographic bleach-fixing composition as claimed in claim 10 wherein said bleaching agent is a ferric aminopolyacetic acid complex.

12. A photographic bleach-fixing composition as claimed in claim 10 wherein said bleaching agent is a water-soluble salt of ferric ethylenediaminetetraacetic acid.

13. A photographic bleach-fixing composition as claimed in claim 10 wherein said bleaching agent is the ammonium salt of ferric ethylenediaminetetraacetic acid.

14. A photographic bleach-fixing composition as claimed in claim 10 wherein said fixing agent is ammonium thiosulfate.

15. A photographic bleach-fixing composition as claimed in claim 10 wherein said thiol or salt thereof is present in an amount of from about 0.1 to about 20 grams per liter of solution.

16. A photographic bleach-fixing composition as claimed in claim 10 wherein said thiol or salt thereof is present in an amount of from about 0.5 to about 5 grams per liter of solution.

17. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of diethylaminoethanethiol.

18. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of monothioglycerol.

19. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of L-(+)-cysteine hydrochloride.

20. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of L-(-)-cystine.

21. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of 2-aminoethanethiol hydrochloride.

22. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of cystamine dihydrochloride.

23. A photographic bleach-fixing composition as claimed in claim 10 containing a bleach-accelerating amount of dimethylaminopropanethiol hydrochloride.