US2587841A - Photographic toning and resensitizing process - Google Patents

Photographic toning and resensitizing process Download PDF

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US2587841A
US2587841A US778269A US77826947A US2587841A US 2587841 A US2587841 A US 2587841A US 778269 A US778269 A US 778269A US 77826947 A US77826947 A US 77826947A US 2587841 A US2587841 A US 2587841A
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toning
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ferric
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emulsion
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Alan M Gundelfinger
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Cinecolor Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C7/00—Multicolour photographic processes or agents therefor; Regeneration of such processing agents; Photosensitive materials for multicolour processes
    • G03C7/26—Silver halide emulsions for subtractive colour processes

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  • The-first image printedto the-photographic lemulsion is usuallyof variable density, that is to say,y some portions ofA the imageare of greater depththan others.
  • variable depth imageto produce a second image, more lightl isofcourse eneededin those portions of the nlm Where the rst image is of greater density:
  • An 'object-of m-yinvention is therefore to provide a method Yof ⁇ selectively increasing-the sensitivity of -a photographicV emulsionin proportion tothe density of a variable density image therein.
  • Another object-offmy invention is to provide a method'ofproolucing a rst image in absorbrprocess, Whichimage when the-emulsion is regenerated,”will cause the resultant sensitivity ofthelm to be substantially proportional to the depth or density of said iirst image.
  • a further object Vof v'myy invention is to provide a multiple step toning process for accomplishing the foregoing objects.
  • My4 invention finds one of its most important applications in color processes involving the toning'and/or dye toning of one or more images in the same emulsion and I have found it particularly valuable in processes wherein the-first image produced inthe emulsion is iron-toned to producea- Prussianbluefl-iznage.l
  • lightsensitive silver ⁇ halideV crystals may be formedA from the silver ferrocyanide produced" by toning, as mentioned theffpreceding,paragraph, with either an alkaline reagentsueh as that described more particularly hereinafter, or an acidic reagent suchas4 thoseA taught in II. S. Patent ⁇ No..A
  • the first image in the emulsion, in such a manner that ⁇ the outerstrata thereof are composed of particlessuch as-grains .or granules which,are,
  • the photographic emulsion is exposed to an appropriate color separation negative to produce a latent color-component image in the printed film, which image is then developed, washed, hardened and partially irontoned by any convenient method.
  • a suitable solution for this partial toning operation is as follows:
  • the lm is then treated with a second toning solution in which the formation of the ferricferrocyanide proceeds at a relatively slower rate. From the second treatment with the second solution a higher degree of dispersion of the precipitated ferric ferrocyanide is obtained.
  • This second solution may take one of several forms, all of which, however, act on the same general principle. Four illustrative toning solutions are here listed and the operations and actions of each will be considered separately.
  • the potassium ferricyanide oxidizes the metallic silver to produce silver'ferrocyanide and potassium ferrocyanide.
  • the oxalate ions combine with ferric ions to form ferric oxalate complex ions, and the ferric ions which do not enter into the ferric oxalate complex combine with ferrocyanide ions to form ferric-ferrocyanide (Prussian blue). It isy the rate of formation of this ferric-ferrocyanide which must be controlled and I have found that the best method of controlling the same is to control the number of ferric ⁇ ions available at any instant for reaction with the ferrocyanide ions.
  • the speed of the reaction is controlled by sdecreasing the amount of alum (potassium or chromium aluminum sulphate) with the result that less of the oxalatel ions are used in forming aluminum or chromium oxalate complex and consequently there are more oxalate ions to combine with the ferric ions to form ferric oxalate complex.
  • alum potassium or chromium aluminum sulphate
  • the pH of the solution is higher, i. e., the hydrogen ion content is lower than in the rst toning solution.
  • the hydrogen ion content is lower than in the rst toning solution.
  • fewer oxalate ions combine with the hydrogen ions to form oxalic acid, thus leaving a greater number of oxalate ions to combine with ferric ions to form the ferric oxalate complex. Consequently, there are fewer ferric ions present at any instant in the solution for the formation of ferric ferrocyanide and the reaction proceeds relatively slowly, re-
  • Figure I is a side elevation of a photographic emulsion situated upon a conventional lm support and having a developed silver image present therein.
  • Figure II is a similar view illustrating the emulsion subsequent to the first toning step in which an upper stratum of the developed silver image is toned to produce relatively coarse ferric ferrocyanide particles and silver ferrocyanide particles.
  • Figure III is a similar view showing the emulsion subsequent to the second toning step in which silver halide particles and a lower stratum ern-v bracing relatively ne ferric hydroxide particles and silver halide particles.
  • the silverferrocyanide formed by the reaction of the lblue toning solution on the silver image is insensitive to light and isl spontaneously redevelopable in developing solutions while silver bromide is light sensitive-'and relatively much less susceptible to spontaneous development, it is necessary to convert the silver ferrocyanide to silver bromide. This may be accomplished in one of two ways; by adding a soluble bromide to the blue toning solutions, or by treating the lm subsequent to the blue toning step with a solution of soluble bromide such as for example, a .2l/2% solution of potassium bromide.
  • the latter method is preferred because as can be seen from the chemical reactions involved in the blue toning step the contrast of the blue toned image may be maintained at a lower value consistent with good color reproduction.
  • the solution used to convert the silver ferrocyanide may be alkaline in character as more particularly described hereinafter, or an acidic medium such as those taught in U. S. Patent No. 1,538,816 to Ives.
  • the silver bromide Which is formed in the deeper strata of the image is more sensitive than the silver bromide formed in the outer strata of the image since that in the deeper strata is formed in the presence of more highly dispersed insoluble particles.
  • ferric ferrocyanide Since the ferric ferrocyanide is subsequently affected by the developing solution for the second image in such a manner that it is converted partially to ferric hydroxide and partially to ferrous hydroxide, depending upon the relative quantities of reducing agent or agents and hydroxyl ions of the developer, and therefore results in a non-uniform restoration of the original amount of ferric ferrocyanide in later steps in the process, it is desirable to convert the ferric ferrocyanide completelyV to ferrie hydroxide prior to the second development stage because of the extremely small solubility product of the latter which makes it substantially non-reactive with reducing agents.
  • One method of accomplishing this result is to treat the film With an alkaline solution, such as, for example, a 2.5% solution of sodium carbonate which converts the Prussian blue to ferric hydroxide.
  • the conversion of the ferric ferrocyanide to ferric hydroxide and the re-sensitizing of the film may be carried on in one step by using a solution composed substantially as follows:
  • the :latent image produced thereby is developed and colored by any convenient process such as. toning. ⁇ or dye toning, and the ferric hydroxide of the original image maythen be reconverted to Prussian blue, as described in United' States Patentv No.v 2,218,001.
  • V5. The process of claim 1 in which the emulsion is resensitized With an alkaline aqueous solution containing bromide ions to convert the silver ferrocyanide to silver bromide and the ferric ferrocyanide to ferrie hydroxide.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Silver Salt Photography Or Processing Solution Therefor (AREA)

Description

March 4, 1952 A. M. GUNDELFINGER PHOTOGRPHIC TONING AND RESENSITIZING PROCESS Filed 001'.. 6. 1947 IN VENTOR ATTORNEYS Patented Mar. 4, 11952 UNITED STATES EArELNr PHOTOGRAPHIC TONING AND RESENSITIZ.- ING PROCESS tion: In-some-instancesethe first image is coloredV by toning lor other "convenient Vprocess prior to the second printingoperation, and in somevcases itis converted toa formA which Will be-more -stable during subsequent operations.
The-first image printedto the-photographic lemulsion is usuallyof variable density, that is to say,y some portions ofA the imageare of greater depththan others. variable depth imageto produce a second image, more lightl isofcourse eneededin those portions of the nlm Where the rst image is of greater density: However, I-have found thatoften in producing a; satisfactory second image through the denser portions ofthe rst image, overexv posure is obtained in those portions of-the'lm wherefthe first image' isv relatively thin oris not present "at all.
An 'object-of m-yinvention is therefore to provide a method Yof` selectively increasing-the sensitivity of -a photographicV emulsionin proportion tothe density of a variable density image therein.
Another object-offmy invention is to provide a method'ofproolucing a rst image in acolorprocess, Whichimage when the-emulsion is regenerated,"will cause the resultant sensitivity ofthelm to be substantially proportional to the depth or density of said iirst image.
Stated another way, it is an object of my invention to provide a method of sequentially producingvtwoor more photographic images in a single emulsion, the rst image being used to modify the sensitivity of the film so thatit is' substantiallyA proportional to the masking-eiiect`` of theflrstN image.
A further object Vof v'myy invention is to provide a multiple step toning process for accomplishing the foregoing objects.
My4 invention finds one of its most important applications in color processes involving the toning'and/or dye toning of one or more images in the same emulsion and I have found it particularly valuable in processes wherein the-first image produced inthe emulsion is iron-toned to producea- Prussianbluefl-iznage.l
In printingthrough such` a" In general, the preferred form of 'myinvention as appliedto a process `employing iron-toningof the first image andfdye toning `of* the second image, `contemplates producing a firstA latent image principally in the-outer strata of a photographic emulsion, developingjsaid image, toning, theY image Prussian blue in a plurality of steps as hereinafter set forth `in detail', converting said Prussian blue image to a ferrie hydroxide or other inert image, reconverting the silver ferrocyanide formed'by the reaction of the toning bath'and the silver image to silver bromide, printing the second: image to the surface of Asaid Aemulsion. de`` veloping said secondimage, toning or `dye toning the second image and nallyrestoringthegproper color -to said iirst image.
As those skilled intheart are Well aware, lightsensitive silver` halideV crystals may be formedA from the silver ferrocyanide produced" by toning, as mentioned theffpreceding,paragraph, with either an alkaline reagentsueh as that described more particularly hereinafter, or an acidic reagent suchas4 thoseA taught in II. S. Patent` No..A
1,538,816 to Ives.`
It is known that the sensitivity iofcatphotolgraphic emulsion is sometimes increased when the light-sensitive silver halide 4crystalsthereinA are formed in the presence of highly4 dispersjedf` insoluble particles in the emulsion, It is thought that I this Aincreased sensitivity is dueA to, thapresence of .insoluble particles. vadsorbed on the sur-` faceof the silverhalide crystals., Theseadsorbed particlesservefa twofold purposenamely to .seti 11n-crystal latticel stransvnecessary. for latent:- image ,formationand to. actas` developing nuclei.
With this fact inemind- I, convert, theA first,` silver,A image produced, in the ,emulsion `-toan insoluble; silyerfsalnin gthepresence of other insoluble and` relativelyt smaller, particles.v the,` dispersion` of; Whichnvaries directlywith; the densitycor depth ofthefirnage.4 The variationin dispersion ofi these.t
particles Ycan ofcourse A-be accomplished uniform ly byvariation-of the `treating batheduringeconversion; but from afpraetical standpoint it is ad# visable `to produce this differential sensitivityeinA steps or stages. In otherwords, by converting;-
thefirst image. in the emulsion, in such a manner that `the outerstrata thereof are composed of particlessuch as-grains .or granules which,are,
relativelyless dispersed, and the inner ondeeper strata,r of the.l image arecomposed of relativelyl highly dispersed particles (approaching:afgnolecu: lar.y dispersion) i, Weaproducefalght sensitivelayer,
the inner stratasofxwhichf will :haveta higher-nde;` i
gree of sensitivity than those strata near the surface of the image. y
Considering now in detail one preferred form of my invention, the photographic emulsion is exposed to an appropriate color separation negative to produce a latent color-component image in the printed film, which image is then developed, washed, hardened and partially irontoned by any convenient method. A suitable solution for this partial toning operation is as follows:
First toning solution Potassium ferricyanide gms-- to 15 Ferric ammonium sulphate gms-- 14 Potassium alum (or chrome alum) gms-- 14 Potassium oxalate gms-- 19 pH (provided by sulphuric acid) 1.5 Water -liter-- 1 Treatment of the silver image in the above solution converts the outer part or stratum of the image to a mixture of ferric ferrocyanide (Prussian blue) and silver ferrocyanide. The film is removed from this bath prior to the conversion of all of the silver, and at approximately the time when the portions near the surface of the image have been completely toned but before the deeper portions of the image have been completely toned.
The lm is then treated with a second toning solution in which the formation of the ferricferrocyanide proceeds at a relatively slower rate. From the second treatment with the second solution a higher degree of dispersion of the precipitated ferric ferrocyanide is obtained. This second solution may take one of several forms, all of which, however, act on the same general principle. Four illustrative toning solutions are here listed and the operations and actions of each will be considered separately.
" `As with the rst toning solution, the potassium ferricyanide oxidizes the metallic silver to produce silver'ferrocyanide and potassium ferrocyanide. The oxalate ions combine with ferric ions to form ferric oxalate complex ions, and the ferric ions which do not enter into the ferric oxalate complex combine with ferrocyanide ions to form ferric-ferrocyanide (Prussian blue). It isy the rate of formation of this ferric-ferrocyanide which must be controlled and I have found that the best method of controlling the same is to control the number of ferric` ions available at any instant for reaction with the ferrocyanide ions. Considering first thebath dened in column A above, it will be noted that the amount of ferric ammonium sulphate is relatively low as compared to the first toning solution, thereby giving a relatively low total concentration of ferric ions in solution. With a low concentration of ferric ions the reaction forming ferric-ferrocyanide proceeds relatively slowly and the resulting image is highly dispersed. This is perhaps the most obvious method of slowing down the rate of formation of the ferric-ferrocyanide.
In the formula given in column B it will be noted that the amount of. ferric ammonium suly phate is the same as in the first toning solution. However, it will also be noted that the amount of potassium oxalate has been increased which means that there are a greater number of oxalate ions available to combine With ferric ions to form ferric oxalate complex ions. This results in a net decrease of ferric ions available at any instant for reaction with ferrocyanide ions which causes the process to proceed more slowly andy hence a higher degree of dispersion in the resulting image is obtained.
In the example given in column C, the speed of the reaction is controlled by sdecreasing the amount of alum (potassium or chromium aluminum sulphate) with the result that less of the oxalatel ions are used in forming aluminum or chromium oxalate complex and consequently there are more oxalate ions to combine with the ferric ions to form ferric oxalate complex. This results in a net decrease of ferric ions available at any instant for reaction with the ferrocyanide ions which causes the process to proceed more slowly and hence a higher degree of dispersion in the resulting image is obtained.
Referring now to the formula given in column D it will be noted that the pH of the solution is higher, i. e., the hydrogen ion content is lower than in the rst toning solution. With this lower concentration of hydrogen ions, fewer oxalate ions combine with the hydrogen ions to form oxalic acid, thus leaving a greater number of oxalate ions to combine with ferric ions to form the ferric oxalate complex. Consequently, there are fewer ferric ions present at any instant in the solution for the formation of ferric ferrocyanide and the reaction proceeds relatively slowly, re-
sulting in a highly dispersed image.
The invention will be better understood by reference to the accompanying drawings showing one mode of carrying out the process of invention in which two sequential toning steps are employed. Y
Figure I is a side elevation of a photographic emulsion situated upon a conventional lm support and having a developed silver image present therein.
Figure II is a similar view illustrating the emulsion subsequent to the first toning step in which an upper stratum of the developed silver image is toned to produce relatively coarse ferric ferrocyanide particles and silver ferrocyanide particles.
Figure III is a similar view showing the emulsion subsequent to the second toning step in which silver halide particles and a lower stratum ern-v bracing relatively ne ferric hydroxide particles and silver halide particles.
It will be understood of course that the foregoing examples are merely illustrative of various ways of controlling the speed of formation of the Prussian blue image and that other variations and combinations of toning solutions can be used. Likewise, it will be understood that if other metallic tones such, for example, as nickel, copper, Y
cobalt, uranium, etc.,`,are desired. that appropriate formulas will be used in which the solution for=therst;stage ofthe toning-` operation may be substantially.- conventional. and` the subsequent solution or; solutions-` will be adapted toiconvert the'balanceof the .toned images more slowly, resultingin-the image being more highly dispersed in its deeper strata. Since there are a` large number ofknown metallic toningsolutions it is believedv unnecessary to give further examples.
It will also beunderstood of course that the conversion of the. silver image may be accomplishedinthree or. more steps or stages if desired, byy appropriately. .varying the solutionsand time of treatment. in each. However, in most cases a two-tagetreatmentis suflicient.
Since the silverferrocyanide formed by the reaction of the lblue toning solution on the silver image is insensitive to light and isl spontaneously redevelopable in developing solutions while silver bromide is light sensitive-'and relatively much less susceptible to spontaneous development, it is necessary to convert the silver ferrocyanide to silver bromide. This may be accomplished in one of two ways; by adding a soluble bromide to the blue toning solutions, or by treating the lm subsequent to the blue toning step with a solution of soluble bromide such as for example, a .2l/2% solution of potassium bromide. The latter method is preferred because as can be seen from the chemical reactions involved in the blue toning step the contrast of the blue toned image may be maintained at a lower value consistent with good color reproduction. The solution used to convert the silver ferrocyanide may be alkaline in character as more particularly described hereinafter, or an acidic medium such as those taught in U. S. Patent No. 1,538,816 to Ives. As previously stated, the silver bromide Which is formed in the deeper strata of the image is more sensitive than the silver bromide formed in the outer strata of the image since that in the deeper strata is formed in the presence of more highly dispersed insoluble particles.
Since the ferric ferrocyanide is subsequently affected by the developing solution for the second image in such a manner that it is converted partially to ferric hydroxide and partially to ferrous hydroxide, depending upon the relative quantities of reducing agent or agents and hydroxyl ions of the developer, and therefore results in a non-uniform restoration of the original amount of ferric ferrocyanide in later steps in the process, it is desirable to convert the ferric ferrocyanide completelyV to ferrie hydroxide prior to the second development stage because of the extremely small solubility product of the latter which makes it substantially non-reactive with reducing agents. One method of accomplishing this result is to treat the film With an alkaline solution, such as, for example, a 2.5% solution of sodium carbonate which converts the Prussian blue to ferric hydroxide.
If desired, the conversion of the ferric ferrocyanide to ferric hydroxide and the re-sensitizing of the film may be carried on in one step by using a solution composed substantially as follows:
Sodium carbonate grams 25 Potassium bromide do 25 Water liter-- 1 The degrees of dispersion of the ferrie hydroxide image will be substantially the same as the degrees of dispersion of the previously produced ferrie ferrocyanide image and consequently the sensitivi-ty` of VVVthe nlmwill Abe proportional second printing operation.
After the second `printing operation the :latent image produced thereby is developed and colored by any convenient processsuch as. toning.` or dye toning, and the ferric hydroxide of the original image maythen be reconverted to Prussian blue, as described in United' States Patentv No.v 2,218,001.
When in the claims, I use `the term insoluble in referring to a salt or other substance, it will be understood that I mean relatively insoluble in thegparticular solutions use d inthe process, and not necessarily insoluble in all known solutions.,
While I have shown andy describeda. preferred form of my invention, it will be apparent that modications may be made therein withoutdeparting from the` broad features as herein dened. Consequently, I do not wish to be restricted to the particular theories or processes herein described, except as limited by my claims.
I claim:
l. In a process in which a plurality of developed silver images are sequentially produced in a silver halide photographic emulsion by printing a first latent image in said emulsion, developing and toning said rst image to ferrie ferrocyanide, converting the toned rst image to a ferrie hydroxide image, resensitizing the emulsion 'by converting the silver salts present therein to a silver halide, printing a second latent image in the resensitized emulsion with light for which said ferric hydroxide image has high absorption; the method of improving the quality of said second image by imparting to said resensitized emulsion a sensitivity substantially directly proportional to the masking effect of said ferrie hydroxide, which consists essentially of conducting said toning with a plurality of toning solutions in successive toning steps including treating said developed first image, in a first toning step, with a rst toning solution containing ferrie ions, ferricyanide ions, and a complexing reagentifor said ferric ions which suppresses the availability thereof for reaction to form ferrie ferrocyanide, said i'lrst toning step being so controlled as to convert a portion of said developed first image to coarse ferric ferrocyanide particles confined to a surface layer of said emulsion, and subsequently treating said developed rst image in a further toning step with a second toning solution containing ferrie ions, ferricyanide ions, and a complexing agent for said ferrie ions, the proportion of complexing reagent to ferric ions being greater in said second toning solution than in said rst toning solution at the conclusion of said first toning step to make a smaller number of ferric ions available to the ferric ferrocyanide precipitate forming reaction and effect precipitation of ferrie ferrocyanide at a slower rate than in said first toning step, said further toning step being so controlled as to convert an additional portion of said image to particles of ferric ferrocyanide of smaller size than those resulting from said rst toning step and confined to a layer in said emulsion disposed below said surface layer, the relationship between the particle size of ferrie ferrocyanide produced in said toning steps being such as to substantially completely compensate for the masking effect of the ferric hydroxide image.
2. The process of claim 1 in which the complexing reagent comprises oxalate ions.
3. Thepo-css of claim 1 in which the emulsion is resensitized by treatment with bromide ions to convert the silver ferrocyanide to silver bromide.
4. The process of claim 1 in which the emulsion is resensitized by treatment with an aqueous solution of potassium bromide.
V5. The process of claim 1 in which the emulsion is resensitized With an alkaline aqueous solution containing bromide ions to convert the silver ferrocyanide to silver bromide and the ferric ferrocyanide to ferrie hydroxide.
ALAN M. GUNDEIFINGER.
Name Date Ives Sept. 10, 1918 Number Number Name at 1,279,276 Crabtree Sept. 17, 1918 1,538,816 Ives May 19, 1925 1,623,123 Loge Apr. 5, 1927 1,695,284 Ives Dec. 18, 1928 1,930,141 Capstai Oct. 10, 1933 1,934,779 Y Townsend Nov. 14, 1933 1,945,772 Dossonville Feb. 6, 1934 2,218,001 YGundeli'nger et al. Oct. 15, 1940 2,226,639 Schinzel Dec. 31, 1940 2,272,556 Gundelnger Feb. 10, 1942 2,341,079 Butement Feb. 8, 1944 2,396,726 Tremble Mar. 19, 1946 2,415,626 Coote Feb. 11, 1947 2,444,567 Huslk July 6, 1948 OTHER REFERENCES Mees: The Theory of Photographic Process, pages 576 and 577.

Claims (1)

1. IN A PROCESS IN WHICH A PLURALITY OF DEVELOPED SILVER IMAGES ARE SEQUENTIALLY PRODUCED IN A SILVER HALIDE PHOTOGRAPHIC EMULSION BY PRINTING A FIRST LATENT IMAGE IN SAID EMULSION, DEVELOPING AND TONING SAID FIRST IAMGE TO FERRIC FERROCYANIDE, CONVERTING THE TONES FIRST IMAGE TO A FERRIC HYDROXIDE IMAGE, RESENSITIZING THE EMULSION BY CONVERTING THE SILVER SALTS PRESENT THEREIN TO A SILVER HALIDE, PRINTING A SECOND LATENT IMAGE IN THE RESENSITIZED EMULSION WITH LIGHT FOR WHICH SAID FERRIC HYDROXIDE IMAGE HAS HIGH ABSORPTION; THE METHOD OF IMPROVING THE QUALITY OF SAID SECOND IMAGE BY IMPARTING TO SAID RESENTIZED EMULSION A SENSITIVITY SUBSTANTIALLY DIRECTLY PROPORTIONAL TO THE MASKING EFFECT OF SAID FERRIC HYDROXIDE, WHICH CONSISTS ESSENTIALLY OF CONDUCTING SAID TONING WITH A PLURALITY OF TONING SOLUTIONS IN SUCCESSIVE TONING STEPS INCLUDING TREATING SAID DEVELOPED FIRST IMAGE, IN A FIRST TONING STEP, WITH A FIRST TONING SOLUTION CONTAINING FERRIC IONS, FERRICYANIDE IONS, AND A COMPLEXING REAGENT FOR SAID FERRIC IONS WHICH SUPPRESSES THE AVAILABILITY THEREOF FOR REACTION TO FORM FERRIC FERROCYANIDE, SAID FIRST TONING STEP BEING SO CONTROLLED AS TO CONVERT A PORTION OF SAID DEVELOPED FIRST IMAGE TO COARSE FERRIC FERROCYANIDE PARTICLES CONFINED TO A SURFACE LAYER OF SAID EMULSION, AND SUBSEQUENTLY TREATING SAID DEVELOPED FIRST IMAGE IN A FURTHER TONING STEP WITH A SECOND TONING SOLUTION CONTAINING FERRIC IONS, FERRICYANIDE IONS, AND A COMPLEXING AGENT FOR SAID FERRIC IONS, THE PROPORTION OF COMPLEXING REAGENT TO FERRIC IONS BEING GREATER IN SAID SECOND TONING SOLUTION THAN IN SAID FIRST TONING SOLUTION AT THE CONCLUSION OF SAID FIRST TONING STEP TO MAKE A SMALLER NUMBER OF FERRIC IONS AVAILABLE TO THE FERRIC FERROCYANIDE PRECIPITATE FORMING REACTION AND EFFECT PRECIPITATION OF FERRIC FERROCYANIDE AT A SLOWER RATE THAN IN SAID FIRST TONING STEP, SAID FURTHER TONING STEP BEING SO CONTROLLED AS TO CONVERT AN ADDITIONAL PORTION OF SAID IMAGE TO PARTICLES OF FERRIC FERROCYANIDE OF SMALLER SIZE THAN THOSE RESULTING FROM SAID FIRST TONING STEP AND CONFINED TO A LAYER IN SAID EMULSION DISPOSED BELOW SAID SURFACE LAYER, THE RELATIONSHIP BETWEEN THE PARTICLE SIZE OF FERRIC FERROCYANIDE PRODUCED IN SAID TONIGHT STEPS BEING SUCH AS TO SUBSTANTIALLY COMPLETELY COMPENSATE FOR THE MASKING OF THE FERRIC HYDROXIDE IMAGE.
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