JOURNAL OF RESEARCH of the National Bureau of Standards-C. Engineering and Instrumentation Vol. 4C, No.1, January- March 1960
Formation of Silver Sulfide In the Photographic Image During Fixation
Chester I. Pope
(October 23, 1959)
. . A photo.graphic s!h:er im~g e is made ,Permanent (fix ed) aft~r development by bathing It 111 a solutIOn contall1lng thIOsulfate whICh forms a soluble tlllosuifate complex with the residual silver halide. Some of the sil ver in the image is sulfided by the thiosulfate during ~ xat io~. The p~rpo se of this study was to determine the amount of sulfiding of the silver III the Image dunng fi xatIOn of film and paper. The amount of the silver reacting depends on the type of t he light-sensitive layer. Also, during bleaching, the residual thiosulfate in the film or paper reacts with silver in a potassium dichromate-sulfuric acid bleach bath to form silver sulfide. For one paper, it was shown that the amount of silver sulfide which was formed in the bleach bath increased with the increase of the concentration of the residual thiosuifate in the paper. A procedure was developed for the reduction of silver sulfide in an emulsion layer to silver so t hat the silver sulfide may be determined in terms of the optical density of the silv l' deposit. The use of hypo eliminators was investigated and a test pro cedure was found for testing the effectiveness of hypo eliminators. A smaH amount of potassium iodide added to the fi xing bath was found effec t iv e in preventing most of the sulfiding of the silver image during fi xation.
1. Introduction silver sulfide formed in the bleach bath for one paper. A third source of silver sulfide may be traced to the A photographic silver image is made permanent residual silver thiosulfate complex and thiosulfate (fixed) after development by bathillg it in a solution which have not been removed in the washing process containing thiosulfate which forms a soluble thio but have reacted during storage to form silver sulfate complex with the residual silver halide. sulfide. This silver sulfide is present before and Some of the silver in the image is sulfided by the after the silver has been bleached. The silver thio thiosulfate during fixation . The permanence of the sulfate complex eventually decomposes Lo forl11 silver image in processed film and paper is I'elated Lo silver sulfide. The residual thiosulfate, because of the degree of sulfiding of the silver in the image which its labile sulfur, reacts with the silver in Lhe image takes place during fixation and the amount of silver to form silver sulfide, especially at high relative thiosulfate complex and thiosulfate which remain humidities. The effect of excessive sulfiding of the after the washing process. The purpose of this silver image first appears in the areas of low sil ver study was to determine the amount of sulfiding of density, the highlights, causing the image Lone to the silver in the image during fixation of film and become brownish. Eventually silver sulfide, itself, paper. A brown stain or "ghost" image remains may bleach, particularly at high relative humidities when the silver in an image is removed by most and in the presence of excess salts which have not bleaching solutions [1, 5, 6, 7, 8, 9, 11).1 This stain been removed during the washing process [4]. has been identified as silver sulfide [1, 2, 3]. Levenson and Sharpe [11] made an intensive study The silver sulfide residue which remains when a of the role of thiosulfate in the formation of silver silver image is bleached may have three sources. sulfide stains in a bromide emulsion during the The first is the reaction of the silver in the image bleaching process. They found that the stain was with the thiosulfate during fixation. The amount produced after the silver image had been in contact of this sulfiding of the silver depends on the type of with thiosulfate either in the developer or after fixing the sensitized emulsion. This silver sulfide is in a sodium thiosulfate fixing bath. They exposed present before and after the silver has been bleached. their samples to a step wedge and plotted the silver The second source of silver sulfide is the residual density and the stain density against relative values silver thiosulfate complex and thiosulfate which of the logarithm of exposure to show the amount of have not been removed in the washing process and stain produced by the corresponding silver densities have not yet reacted with the silver in the image to for a bromide fine-grain emulsion. They concluded form silver sulfide but do react in the bleach bath. that a certain amount of thiosulfate was strongly This reaction was used to study the effect of different absorbed on the silver of the image as thiosulfate residual thiosulfate concentrations on the amount of or as a thiosulfate complex and that it reacted with silver ions in the bleach to form silver sulfide. This
1 Figurcs in brackets indicate the literature references at the end of this paper. subject is discussed further in section 6. 65 530231- 60- 5 2 . Processing Procedures The permanganate bleach converted the silver sulfide to silver chloride. The potassium bromide Samples of the photograpbic film and paper were in the clearing bath prevented the loss of silver in cut to 1% in. by 10 in. and exposed to a step wedge. the gelatin layer because silver chloride is more Not more than eight samples were proccssed or soluble than silver bromide. There was a partial treated at one time. About 2 liters of fres h solu tio n solution of the sil ver chloride when sodium chloride were used in each processing operation cmploying was used in the clearing bath. Unfortunately, the nominal 8- by 10-in. enameled trays. The samples gelatin layer was quite soft afLer treatment in the were continuously agitated by hand during process clearing bath and the high alkalinity of most de ing and washed in running tap water. The process velopers caused the gelatin to break loose from the ing solutions arelisteu in the appendix, section 8. The support. The amidol developer was found to be temperature of the processing solutions were at room satisfactory for papers and most films. However, temperature (22° to 28° C). films with a normally soft gelatin layer should be washed 5 min after treatment in the cloaring bath, 2.1 . Developing and Fixing the Silver Image Lreated 5 min in a 2-percent solution of formaldehyde, Tho samples wer e devoloped 3 min, treated 1 and washed 10 min before drying. min in the short stop bath, and fixed 10 min in two T he r eduction of silver sulfid e in the gelatin baths (5 min in cach bath). Next t he samples were layer to silver appeared to be quantitative. When rinsed 1 min in tap water , treated 10 min in the this reduced silver was sulfided the original silver hydrogen peroxide eliminator No.1, bathed 2 min sulfide densities were again obtained. The silver in a I-percent solution of sodium sulfite, washed was sulfided in an atmosphere of hydrogen sulfid e. 30 min, and hung to dry at room temperature. Two The sample of film or paper was eoaked in water for fixing baths wer e used to facilitate tbe removal of 5 min and, after r emovin g the surface water with a the silver t hiosulfate complex. T ests showed that blotter, it was suspended for 1 hI' in a ?f-ga llon the amount of silver sulfide formed in the silv er bottle above a solu tion oontaining 50 g of sodium sul imago during fixation reached a maximum in about fide (N azS· 9H20 ), 35 g of citric acid (H3C6H50 7· I-IZO), 3 min in the acid-hardening fixing bath. and 500 ml of water. After this treatment t he sample was washed for 30 min in r Ullnin g tap water. 2.2. Bleaching the Silver Image The samples wer e treated 5 min in tho dichromate 3. Removal of the Thiosulfate During the bleach bath, washed 30 min in tap wator at 25 °± Washing Process 2° C, treated 5 min in tho clearing bath, treated ;) min in the thiosulfate eliminator No.3, and washod The thiosulfaLe must be removed from processed 30 min in tap water. The operation was performed films and papers when investigating the reaction of in daylight but not in direct sunlight. Tho bleach thiosulfato with the silver of the image during removed tho silver , leaving the silver sulfide which fixation. Solutions which remove the thiosulfate formed during fixation. Additional silver sulfide from the gelatin layer and paper base are generally was formod when the silver thiosulfato complex or known as "hypo eliminators." Crabtroe et al. [1 3] residual thiosulfate was present. The potassium showed that hydrogen peroxid e in an ammoniacal dichromate-sulfuric acid bleach oxidized the sil ver solution eliminates thios ulfate from photographic in the image in 1 to 2 min. The bleach did not materials. The hydrogen peroxide oxidizes the dissolve the silver-sulfide residue when the bleaching thiosulfate to sulfate. This hypo eliminator was time was ex tended to 15 min. The clearing bath, used in the experimental ,vork reported in this which was used to remove the residual diohromate, paper and is listed as formula No. 1 in the appendix , was t he on e employed by Levenson and Sharpe section 8.1. It is the same hypo eliminator used in [11] and proved to be quite satisfactory for both an American Standards Association photographic films and papers. It was found necessary to fix the standard [16 ]. samples after clearing to remove the last traces of Salt solutions have proved effective in removing silver salts which, when present, increased the the thiosulfate from films and papers [12 , 13 , 14 , 15] . density of the silver sulfide residue slightly. Such solutions are convenient because they can be prepared and stored before use and no temperature 2.3. Reduction of the Silver Sulfide to Silver control is necessary. In the course of this study two The samples were treated 2 to 3 min in the pe1' sal t solutions were developed which proved to be manganate bleach bath, rinsed 10 sec in running tap quite efficient in removing the thiosulfate. On e water, treated 5 min in the clearing bath, washed 30 solution contained sodium sulfate and ammonium min in running tap water, blotted to r emove surface hydroxide and the other sodium sulfate and sodium water, and dried in the dark. The samples were sulfite. The sodium sulfate helps to prevent undue then exposed for 10 min to a 100-w tungsten lamp swelling of the gelatin caused by the alkalinity of at a distance of 12 in., developed 5 min in running the sal t solutions. The formulas for these solutions tap water, and hung to dry. vVith the exception of are li sted as No.2 and 3 in the appendix, section the drying of the samples before exposure the oper 8.1. Tho two salt solu tions have b een used in ations were performed in daylight but not in direct experimen tal studies only and have not been evalu- sunlight. , ated for use in large-scale production. The sodium 66 thiosulfate content of single-weight samples of photo 1.60 copy, contact, and enlarging papers was reduced to 0.005 mg or less per square inch when treated in these solutions. When the hydrogen peroxide hypo 1.20 eliminator No. 1 was used no sodium thiosulfate could be found in films or papers. The r esidual thiosulfate in photographic papers was determined .80 by the method of Crabtree et al. [17] and in photo graphic films by the method of Crabtree and Ross [22] . 4: 'oL--O-->L---' ~ ::::- " 4 . Results and Discussion 000 0. 5 0 1.00 1.50 2 .00 2.50 3.00 RELATIVE LOG EXPOSURE 4.1. Silver Sulfide Formed in Photographic Papers During Fixation "FIGURE 1. Reflection density veTSUS 1'elat1:ve loga1'ithm of ex posure for the silveT image, the silver sulfide 1'esidue, and The paper sample \vas exposed Lo a sLep wedgc, the silver obtained by the reduction oj the silvel' sulfide, fOT processed and treated in Lhe hydrogen pCl'oxide one sample of a single-weight photocopy paper. hypo eliminaLor No. 1 after fixation. The silver image was remov cd by the potassium dichromate sulfuric acid bleach leaving the silver sulfide image 2.00
or residue which in turn was reduced to silver. A, ImoQ e During the above procedure reflecLion densi ty 2 measurements were made of th e original silvcr image, 1.6 0 the silver sulfide image remaining aftcr (h e bl each, ~ >- and th e silver image obLaincd by reducing the silvcr in sulfide to silvcr. No filter was used in m easuring :5 1.20 0 the densities of the silvC'r sulfide. T]le d(m sity of / the paper base was subLracLed from Lh e densiLy 0 ~ .80 - readings. The dCllsi Lies fOl' Lhe (~ hr C'() images ob , " tained from a single sample were plotLed against '"a- relativC' valucs of t il(' logarithm of exposure and (he .4 0 three ch aracLcl'isLic curves are sllOwn in fi gul'es 1, 2, alld 3, respecLively, for a photocopy paper, a co ntact paper, alld a n enlarging paper. The papcrs were all .00 C>- single weight. Thc lowest cu rve ill figures 1,2, and 0 .50 1.00 1.50 2.00 2.50 3.00 3 shows t hc densiLy of t he silver sulfide fOl'nwd ill RE I AliVE LOG EXPOSUHt th e image during fixaLion. Tile middle curve shows FIGURE 2. R eflect1:on den sity ve1'S1lS Telative 10gaTithm of the density of Lhe silver which is obtain ed by reduc exposure JOT the silver image, lhe silver sltl fid e Tesidue, and ing the silver sulfide Lo silver. The percentage of the silvel' obtained by the reduction oj the silver w lfide, JOT the original image silver sulfided during fixation may one sample oj a single-weight contact paper. be determined from the density reading in th e middle curve and the corresponding density reading in the highest curve which is that for the original silver 2.00 image. In the region of high-silver densiLies or full exposure the amount of sulfiding of the silver image Ag Image is about 25 percent for the photocopy paper, about 1.60
17 percent for the contact paper, and about 28 per > > cent for the enlarging paper. At lower silver in ~ 1.20 densities the amount of sulfiding of the silver image o z is about 20 percent for a density of 0.6 for the o photocopy paper, about 9 percent for a silver density i= ~ .8 0 of 1.0 for the contact paper, and about 14 percent w no for a silver density of 1.0 for the enlarging paper. The percentage of the silver sulfided increases as the .4 0 silver density in the image increases up to the high densities. The amount of silver sulfide formed .0 0 L o--t!"'-<>--"''---'-----'------"------'---' reaches a maximum in the high densities and levels 0.00 0.50 1.00 1, 50 2.00 2. 50 off as shown by the curve for silver sulfide in figures RELAT IVE LOG EXPOSU RE 1,2, and 3. "FIGURE 3. R eflection density VeTSllS Telative logarithm of ex pOSUTe faT the silver image, the silver sulfid e Tesidue, and the silveT obtained by the Teduction of the silver sulfide, fOT 2 The rcO ection density was measured by the American Standards Association method [10] . one sample of a single-weight enlarging paper. 67 The above results demonstrate that an appre 4.2. Silver Sulfide Formed in Photographic Films ciable amount of the silver in the image of photo During Fixation graphic papers is sulfided during fixation. The silver sulfide cannot be removed by washing or the The amount of sulfiding of the silver image during use of hypo eliminators. If photographic papers arc fixation was determined for two microfilms a photo to be used for permanent records the thiosulfate mechanical film, and an X-ray film by 'the same must be removed or reduced to the lowest possible procedure as that described for photographic papers concentration during the washing process to prevent except that the densities were measured by trans the formation of additional silver sulfide. R esidual mitt~~ light. No tilter was used in measuring the thiosulfate in the processed paper reacts with the denSItIes of the silver sulfide. The transmission silver in the image to form more silver sulfide. densities were plotted against relative values of the This reaction is slow at low relative humidities but logarithm of exposure. From the characteristic quite rapid at high relative humidities. Further curves obtained for each film the density of the sulfiding of the silver image would be especially silver sulfide and silver obtained when the silver objectionable in areas of low silver densities cor sulfide was reduced to silver were determined for responding to the highlights of pictures. The various densities of the original silver image. The amount of the sulfiding of the silver in films and results are tabulated in table 1. The characteristic papers depends on the type of emulsion. curves for microfilm A are shown in figure 5. The Transmission density measurements were also results in table 1 show that the amount of sulfiding made of the silver and silver sulfide in this study on of the silver image in the high densities is about 7 the sulfiding of the silver image in papers during percent for microfilm A and 5 percent for microfilm fixation. The transmission density of a paper base B. These values compare well with the 5 percent depends on the optical system of the transmission found by Levenson and Sharpe [11] for a bromide densitometer; however, if the same densitometer is fine-grain emulsion. This amount of sulfiding of used in a series of tests useful relative data are the silver image during fixation should have a negli obtained. For example, transmission density meas gible effect on the permanency of the image in urements were made of the same sample of photocopy microfilm. However, the residual thiosulfate must paper which was used for figure 1. The densities be removed in the washing process to prevent were plotted against relative values of the logarithm further sulfiding of the silver image. of exposure and the three characteristic curves are As in the case of photographic papers, the amount shown in figure 4. The density of the paper base of sulfiding of the silver image in films depends on has been subtracted from the density readings. the type of emulsion . The values for the photo- The curves in figure 4 show approximately the same percentage of sulfiding of the silver image for the highest silver densities as those in figure 1 but in the lower silver densities the transmission density 3.20 measurements show a higher percentage of silver sulfided than the reflection density measurements. 2.80 This was found to be true also for contact and enlarging papers. 2.40
>- f-- Vi 2.00 z w 0 z I 20 0 Vi 1.60 '!' ~ AQ Image '::: '"Z "' "'<1 ~ . S O a: 1.20 0 >- z Q "' "' Agz S - Ag .so ~ 40 Z
FIGURE 4.. Transmission density versus relative logarithm of eX pO S1!re for the silver image, the silver sulfid e residue, and FIGURE 5. Transmission density versus Telative logarithm of the silver obtained by the reduction of the silver sulfide, for exposure for the silver image, the silver 8llifide Tesidue, and the same sample of single-weight photocopy paper shown in the silver obtained by the Teduction of the silvel' sulfide, for figure 1. one sample of microfilm A.
68 mechanical and X-ray films are given in table 1 normally IOl'lned dUl'ing fixaLion . This Lype of to show the difference in types of emulsions in test for residual LhiosulfaLe in papers and films films . A silver sulfide density of 0.02 was obtained shows Lhe direct effect of Lhe residual thiosulfaLe for a silver density of 1.8 for one cine fine-grain on the silver in Lhe linage and should sin1l11aLe the film not shown in the table. reaction of residual thiosulfate with Lh e silver in the image during storage. The Crabtree et al. [17] TABJ, E J. Densities of the silvel' image method for determining thiosulfate in paper m easures in films and the cOI'1'es ponding densi ties of the silve1' sulfide residue and the thiosulfate concentration in a clear area of the the silve1' obtained by the 1'eduction of paper . the silve1' sulfide If residual thiosulfate is present when papers are bleached , some silver sulfide may be precipitated Densi ty of the in the paper base. Reflection density m eaSUl'es Density of the Density of sil sil vCr obtained silver image ver sulfide aftor by Lhe red uc only the density of silver and silver sulfide in the bleach tion of the sil- gelatin layer. For this reason, transmission density vcr sulfide is recommended instead of reflection density for
IVficrofi lm A measuring the silver sulfide in papers as a tes t procedure for evaluating hypo eliminators. U.50 0.05 0.05 The effect of different residual thiosulfate concen 1.00 .07 .07 1. 50 .OS .10 trations in paper on the increase of the density of 2.00 . 11 . 14 the silver sulfide is shown in figure 6. Samples of a 2.50 . 13 . 18 3.00 . 15 .20
Microfilm B 200 .------~------, ~ Ag Image
0.50 0.02 0.03 I. 00 .03 . 05 I 60 I. 50 .04 .Ou 2.00 . 06 . O~ ,. 2.50 . U8 . 11 .... 0. 00 . 10 . 14 '" I 20 "cO' L Photomec hanical nlnl '2 '" 0.50 0. 00 0.08 '"~ 8 0 1.00 .06 . 12 " 1.50 . 09 . 18 ~ 2. 00 . 12 .22 2. 50 . 14 .26 40 0. 00 . 17 .28 3.50 . 19 .30 4. 00 .20 .31 o X·ray film 3.00 (2 li ght·se nsitive cm ulsio ns) REL AllVE LOG EXPOSURE
0.50 0. 04 0. 05 1.00 .06 .08 FIGURE 6. T he e.fJect of the l'esidual sodium thiosulfate 1. 50 . 08 . 12 concentmtion on the amount oJ silver sulfid e f o1'1ned in the 2.00 . 10 . 14 2.50 . 12 .17 bleach bath is shown faT a single-weight contact pape1'. 3.00 . 13 . 19 Oharacteristic curves are given for the original silver imagc and for the silver 4.00 .16 . 23 obtained by the reduction of the silver sulfid e formed with varying concentra tions of residual sodium thiosulfate. The concentration of thc residual sodium thiosulfate is shown at the end of t he curves.
4 .3. A Test for Hypo Eliminatols single weight contact paper were given the same The potassium dichromate-sulfuric acid bleach exposure to a step wedge and processed in the same which was used in this investigation removes the silver manner and at the same time except that, after from the photographic image, leaving the silver fixation, one sample was treated in the hydrogen sulfide formed during fixation by the reaction of peroxide hypo eliminator No. 1 and one sample was thiosulfate with the silver image. Also, any residual washed in tap water for each of the following wash thiosulfate reacts with silver ions in the bleach ing times : 120, 60, 30, and 10 min. The samples bath to form additional silver sulfide. It seem ed were bleached and the silver sulfide was reduced to feasible to use the latter reaction to determine the silver. The transmission densities of the silver effect of different thiosulfate concentrations on the image and the silver of the silver sulfide reduced to silver image by measuring the increase in the silver silver were plotted against relative values of the sulfide density above that fOlUld when the residual logarithm of exposure. The density of the paper thiosulfate is completely eliminated by the hydrogen base was subtracted from the density readings. The peroxide hypo eliminator No. 1. A concentration lowest CUl've shows the silver of the image sulfided of 0.005 mg of sodium thiosulfate eN a2S20 3) pel' during fixation, where all of the residual thiosulfate square inch in photographic papers gave a m easurable had been removed by the hydrogen peroxide hypo increase in the silver sulfide density above that eliminator No. L The curve for the original silver 69 image was ob tained from the sample which had been that a small amount of the iodide ion in the fixing treated in the hydrogen peroxide hypo eliminator bath is quite eff ective in preventing most of the No. 1. The other curves fall in order of their residual normal sulfiding of the silver. W118n processed thiosulfate concentrations which are given in milli samples of film or paper, which had been fixed in the gram s of sodium thiosulfate eN a2S20 3) per square acid fixing bath containing potassium iodide, were inch at the end of the curves. The curves show again treated in the acid fixing bath containing no that the silver sulfide increases appreciably as the iodide ion, the amount of sulfiding of the silver was residual thiosulfate increases. For a silver image almost as great as that normally obtained. density of about 1.9 the sample containing 0.008 mg The eff ect of the iodide ion in preven ting the for of sodium thiosulfate per square inch shows a 57 mation of silver sulfide in the silver image would percent increase in th e sulfiding of the silver above suggest that silver ions were presen t in the fixing that taking place during fixation and the sample bath. Silver iodide instead of silver sulfide would containing 0.07 mg of sodium thiosulfate per square be formed because it is less soluble than silver sulfid e. inch shows 111 percent in crease. It is not known what eff ect any residual silver iodide The above results show that the efficiency of a or potassium iodide might have on the stability of hypo eliminator may be evaluated by testing it the silver image. Small concentrations of the iodide against the hydrogen peroxide hypo eliminator No. 1 ion in the fixing bath retards the rate of fixation [20] used as a standard. This test may be made b:v and decreases its fixing capacity. giving samples of film or paper from the same roll or box the same exposure to a step wedge and proc essing them at the same time in the same solutions 6. Silver Sulfide Formed During Fixation in except that, after fixation , one set of samples is a Thiosulfate Fixing Bath treated in the hypo eliminator to be tested and the other in the hydrogen pero:\.'ide hypo eliminator No.1. R eindorp [1] postulated that the silver sulfide The samples are then bleached and the transmission was formed during fixation by the decomposition of densities of the silver sulfide are measured and a silver thiosulfate complex. Levenson and Sharpe plotted against relative values of the logarithm of [11] concluded tha,t the thiosulfate was absorbed as exposure. For greater sensi tivity the silver sulfide a simple ion or a complex ion on the silver in the may be reduced to silver. The characteristic curve image during fixin g and tllat the silver sulfid e was for the hy drogen peroxide hypo eliminator No. 1 form ed in the bleach bath by the reaction of silver shows Lhe silver sulfid e formed during fixation. The ion s with the absorbed thiosulfate. If the thio characteristic curve for the hypo eliminator being sulfate is absorbed as a simple ion or as a complex tested will be th e same jf all of the residual thiosul ion on the surface of the silver grains it migh t be fate has b ee n eliminated bu t will br higher if residual possible to el imi nate it and prevent the formation of tbiosulfate is presen t. I ts height will depend on the silv er sulfide. Eu t, if the silver sulfide is formed concen tration of the residual thiosulfate as shown during fixation it could not be removed and would in figurc 6. b e an integral part of the image. This problem was investigated and the experimental results gave strong evidence that the silver sulfide is formed during 5. Effect of Potassium Iodide on the Forma fixation. tion of Silver Sulfide During Fixation 6 .1. Experimental Results The addition of potassium iodide to the fixing bath a . Removal of the Silver Sulfide From the Silver Image has been found to preven t the formation of the brown silver sulfide stain which interferes in reversal An investigation was made to determine if the and reduction operations [7 , 18, 19]. Murray [18] silver sulfide, which formed during fixation, could be added three-fourths of an ounce of potassium iodide r emoved from the silver image before it was bleached. to one gallon of the fixing bath. Crabtree et al. [7] A solution containing 30 g of silver nitrate and 180 g found that 0.1 to 1.0 percent of potassium iodide in of anhydrous sodium sulfite per liter was found the fixing bath eliminated the brown stain in positive capable of removing all of the silver sulfide from a film. sulfided silver strip. A similar solution was used by The eff ect of potassium iodide in the acid fixing Hickman and Weyer ts [21] in their studies on optical bath on the sulfiding of the silver image was investi intensification of silver sulfide images. gated . One gram of potassium iodide was added to A brown coating of silver sulfide was formed on each liter of the fixing bath. The samples were given silver strips, %-in. by 5-in. and O.Ol-in. in thickness, a full exposure, developed, fixed, treated in the hydro by exposing them to an atmosphere of hydrogen gen peroxide hypo eliminator No. 1, and bleached . sulfide gas for 1 to 4 hr. The strips were first cleaned The density of the silver sulfide ranged from 0.02 to in glacial acetic acid, washed, and then suspended 0.04 for contact and enlarging papers which nor in an atmosphere of hydrogen sulfide. The silver mally yielded a silver sulfide density of 0.2 to 0.25 . nitrate-sodium sulfi te solution removed the silver The density of the silver sulfid e was about 0.005 for sulfide layer from the silver in 2 to 6 hr at room two microfilms which normallv vielded a silver sulfide temperature and in diffuse daylight. The time re density of 0.10 to 0.15. The deilsities were measured quired for the removal of the silver sulfide layer by transmission without a filter. These results show depended on its thickness and the intensity of the 70 light. This test shows that the silver nitrate-sodium sulfate in papers. The solution used ilt this test sulfite solution dissolves silver s ulfid e. contain s silver nitrate and sulfuric acid and reacts Processed samples of 2 microfilms, a contact paper, quantitatively with thiosulfate to form silve)' sulfide. and an enlarging paper were treated for 2 111' in the Several test were made on paper sam.ples wi th high silver nitrate-sodium sulfite solution in difruse day silver densities (full exposure) but no in crease in the light at 25° C, washed for 30 min ill tap wa ter, and dell sityof the silver image could be detected. This bleached. The densities were measured by trans indicated that no thiosulfate was presen t in an mission without a filter . These samplcs had been absorbed state on the surface of the sil ver in the treated in the hydrogen peroxide hypo eliminator image. These sam e paper samples yielded a silver No. 1 during processing. For areas of hi gh sil ver sulfide residue with a density of 0.20 to 0.25 when the densi ty of almost full exposure the sil ver sulfide silver wa s removed by the bleach bath. These density in microfilm A was reduced from 0.] 0 to 0.00; results indicated that the silver sulfide obtained after microfilm B, 0.15 to 0.005; a contact papcr, 0.20 to bleaching was fonned during fixation and not in the 0.07; and an enlarging paper, 0.26 to 0.09 . The first bleach bath by the reaction of silver ions with value in each case was the normal silver-sulfide absorbed thiosulfate. density obtained when the silver image was bleached. The silver sulfide image or residue, left in the 6.2. Formation of the Silver Sulfide gelatin layer of papers after the removal of the silver It is well known that thiosulfate in a fixing bath by the bleach bath, wa s only slightly dissolved by attacks the silver in a photographic image and the the silv er nitrate-sodium sulfi te solution under the rate of attack depends on several factors such as the above experimental conditions but, when exposed to composition of the bath, acidity of the bath, temper direct sunlight during treatment for 4 hI' at 28° C, ature, and agitation [23). The silver ion reacts with JJ1.ost of the silver sulfide was removed. D ensities the thiosulfate anion to form silver sulfide. Experi of 0.2 to 0. 3 of silver sulfide residu e in papers were men tal evidence in dicates that the silver in the image reduced to a density of 0.04 . It was necessary to is oxidized in the fixill g bath in the presence of reblea ch th e samples to remov'c' the silver deposited oxygen [3 , 23) and this reaction would be a source of by the silver nitrate-sodium slllfi te solutioll in th e silver iOll s. Reindorp [1) suggested that s ilver ion s gelatin layer and paper ba se. may be formed in the lixin g bath by a seconclary The abov e results indicate that silver sulfid e was dissociation of the ani011s of a silver thiosulfate formed 011 th e silv er image during fixation. complex. :More in formation is necessary to establish the exact mechanism of th e formation of silver b. Staining Effect of the Fixing Bath on a Silver Surface sulfide in th e silver image during fixation . Glass plates, 3-in . by 4-in., were coated with silver It is to be no ted that no silver sulfide residue is by the Rochelle salts process. The silver coated obtain ed when the silver image is bleached if fixa plates were partially immersed in an acid or neutral tion takes place in a 2-percen t solu tion of po tassium fixing bath for 1 min alld washed. A brown stain cyanide bu t, if a silver image whi ch I as been fixed was clearly visible on the surface of the silver in that in potass ium cyanide is exposed to an atm.osphel'e of area treated in the fixing bath. The brown stain hydrogen sulfide gas for a few minutes, a silver was more pronoun ced when wet hut still visible sulflde residue is obtailled whell the silver is removed when dry . III thc blcach bath. Silver strips, %-i11. by 5-i11 . and O.OI-in . in thick ness, were treated in a solution containing 60 ml of 7. Summary and Conclusions distilled water and 40 111.1 of concen trated nitric acid, Silver sulfide forms in the silver image of photo and wa shed. This operation produced a fine white, graphic materials during fixation. The perce ntage of mat surface on the silver strip. The silver strips, th e silver sulfide in the image is small in microli.lms wet or dry, were partially immersed in an acid or bu t is quite large in photographic papers as shown in neutral fixing bath for 10 sec and washed. In each section 4. The thiosulfate which is not removed by case a brown stain was clearly visible on that portion the washing process causes further sulfiding of the of the strip treated in the fixing bath. The brown image. The extent of the sulfiding depends chiefly stain was assumed to be silver sulfid e. These tests on the concentration of the residual thiosulfate and show that the thiosulfate in the fixing bath reacts the storage conditions. If th e photographic image is rapidly to stain mirror and fine mat silver surfaces to be used for permanent or archival records, the and it would be expected that the silver in a photo thiosulfate must be removed as completely as pos graphic image would react in a like manner with sible during the washing process. If the thiosulfate thiosulfate in the fixing bath to form silver sulfide is not sufficiently removed by the wash water, it during fixation . may be necessary to use a hypo eliminator. Hypo eliminators may be evaluated for th eir effi c. Conversion of Absorbed Thiosulfate to Silver Sulfide ciency by comparing them with the hydrogen per It should be possible to increase the density of the oxide hypo eliminator No. l. A solution of sodium silver in the image by convertin g any thiosulfate sulfate together with either sodium sulfite or am absorbed on the silver to silv er sul1ide. Contact and monium hydroxid e will reduce the hypo (sodium enlarging papers were subjected to the Crabtree et thiosulfate, N a2S20 3) con tent of single-weight papers a1. [17) hypo test used for determining residual thio- to 0.005 mg or less pel' square inch. 71 The effect of different residual thiosulfate concen After fixation the sample of film or paper is rinsed trations on the sulfiding of the silver image can be 1 min in running tap water, treated for 10 min in determined by measuring the density of the silver the above solution, bathed for 2 min in a 1 percent sulfide formed when the image is bleached. The solution of sodium sulfite to remove the excess thiosulfate reacts with the silver ion in the bleach hydrogen peroxide, and washed 30 min in running bath to yield silver sulfide and the density of the tap water. silver sulfide increases as the residual thiosulfate No. 2 concentration increases. This method would be more rapid than the oven aging tests used by Crab Sodium sulfate, anhydrous ______140 g. tree and Ross [22] and in an American Standards Ammonium hydroxide (28 %) ______2 ml. Association specification [16] to determine the effect Water to make______1 liter. of residual thiosulfate on the silver image. Silver sulfide, which remains in the gelatin layer No.3 after the silver is bleached, may be reduced to silver by the procedure outlined in section 2.3. The per Sodium sulfate, anhydrous ______71 g. Sodium sulfite, anhydrous ______63 g. centage of silver sulfide is calculated from the den Water to make ______sities of the reduced silver and the silver in the 1 liter. original image. The addition of potassium iodide to the fixing When hypo eliminators No. 2 and 3 are used, the bath will prevent most of the sulfiding of the silver sample of film or paper, after fixation, is rinsed image which takes place during fixation. The iodide 1 min in running tap water, treated for 10 min in ion increases the fixing time and decreases the fixing the hypo eliminator, and washed 30 min in running potential of the bath. tap water. Experimental evidence is presented to show that silver sulfide is formed in the silver image during fixation. However, more information is necessary to 8.2. Formulas for the Bleaching Process in Which establish the exact mechanism of its formation. the Silver of the Photographic Image Is Removed and the Silver Sulfide Is Left as a 8 . Appendix Residue in the Emulsion Layer 8.1 . Formulas for Developing and Fixing the Silver Image in Films and Papers Bleach Bath Potassium dichromatc ______Develop er 5.0 g. Sulfuric acid (95%) ______5.0 ml. Monomethyl p-aminophenol sulfate ____ _ 3.1 g. vVater to mal,c ______] liter. Sodium sulfite, anhydrous ______45.0 g. H ydroquinone ______12. 0 g. Clearing Bath Sodium carbonate, anhydrous ______67.5 g. Potassium bromide ______L 9 g. Sodium sulfite, anhydrous ______50. 0 g. Water to make ______1 liter. Sodium hydroxide______- -- l. 0 g. Dilutc 1 to 1 before use. 'iVater to make ______1 liter.
Stop Bath Fixing Bath Acetic acid, glaciaL ______12 m1. Water to make ______1 liter. Sodium thiosulfate, N a2S20 3·5H20 ______240 g. Sodium sulfite, anhydrous ______15 g. Fixing Bath Water to make______1 liter. Sodium thiosulfate, N a2S20 3' 5HzO ______240.0 g. Sodium sulfite, anhydrous ______15.0 g. Hypo eliminator Acetic acid (28%) ______48 ml. Boric acid ______Use hypo eliminator No.3 which is listed in section 7. 5 g. 8.1. Potassium aluminum sulfate, KAl(S04)Z ' 12HzO ______- - 15.0 g. Water to make ______1 liter. 8.3. Formulas for Reducing the Silver Sulfide Residue Hypo eliminators in the Gelatin Layer to Silver No.1 Bleach Bath Water ______300 mI . Hydrogen peroxide (30%) ______50 ml. Potassium permanganate ______- - _ -- -- 5. 0 g. Ammonium hydroxide (28 %) ______10 ml. Sodium chloride ______- - _ ------10.0 g. Potassium bromide ______l. 0 g. Acetic acid, glaciaL ______- - - _ -- - - 50 illl. Water to make ______1 liter. Water to make ______1 liter. 72 Clearing Bath [6] A. and L. Lumiere and A. Seye\\'etz, T he composition of the developed image, Brit . J . Photo 59, 61 (1921). Sodium bisulfite ______50. 0 g. [7] J . 1. Crabtree and L. E . Muehler, Reducing and in Potassium bromide ______12. 0 g. trn~ if yi n g solut ions for motion picture film, J. Soc. Water to make ______Motion Pictur(' Engrs. 17, 1025 (1931). 1 liter. [8] J . 1. Crabtree, G. T . E aton, and L. E. Muehler, The removal of hypo and silver salts from photographic Developer materials as affected by t he composition of the proces sing solutions, J. Soc. Mot ion Picture Engrs. 41, 47 Amidol, 2,4-Diaminophenol Dihydro- (1943). . chloride ______[9] C. Lighton, Notes on the bleaching and local reduction 5. 0 g. of bromide prints, Brit. J . Photo 73, 6'13 (1926). Sodium sulfite, anhydrous ______30.0 g. [10] Ameri can Standard Sensitometry and Grading of Photo Water to make ______1 liter. graphic P apers, PH2.2-1953 (America n Standards ASSOCiation, I nc., 70 East 45th St., New York 17, N.Y.) [11] G. 1. P . Levenson and C. J . Sharpe, The role of thio Stop Bath s ulphate in the formation of sulphide stains during bleachillg, J . Phot o Sci . 4, No.4, 89 (1956). Citric acid, H 3C6H 507-HZO ------35 g. [12] H . L. Scott and W. F. H yatt, U.S. P atent 2,688,546 Water to make ______1 liter. (1954). [1 3] J . 1. Crabtree, G. T . Eaton, and L. E. Muehler, The elimination of hypo from photographic images, Am. 8.4. Quality of the Chemicals Used for the Formulas Phot o 35, No.4, 272 (1941). Listed in This Appendix [14] J . 1. Crabtree, and R. W. H enn, IncreaSing the washing rate of motion picture films with salt solutions, J. All of Lhe solutions were made up with distilled Soc. Motion Picture & Television Engrs. 65, 378 (1956) . water. The following chemicals were of reagent [15] R . W. H enn, N. H . King, and J . 1. Crabtree, The effect of salt baths on hypo and silver elimination, P hoto quality m eeting ACS specifications: sodium sulfite, Eng. 7, No.3 and 4, 153 (1956). sodium sulfate, acetic acid, boric acid, potassium [16] American Standard Method for Indicating the Stability bromide, sodium carbonate, citric acid, sodium of the Images of Processed Black-and-White Films, chloride, potassium permanganate, sodium hydroxide Plates, and P apel'R, PH4.12-1954, p . 8 (American Standards ASSOCiation, I nc., 70 East 45th St. New potassium dichromate, ammonium hydroxide, and York 17, N.Y.). sulfuric acid. T he monomethyl p-aminophenol [17] J . 1. Crabtree, G. T . Eaton, and L. E. Muehle!', The sulfate, hydroquinone, sodium thiosulfate, and po quantitative determination of hypo in photographic tassium aluminum sulfate conformed to American prints wit h silver nitrate, J . Franklin I nst. 235, No. 4, 351 (1943). Standard Specifications for Photographic Grade [18] A. Murray, New control methods in chemical retouching, Chemicals. The Amidol \vas Eastman Kodak Cat. Brit. J . Photo 77, 121 (1930). No. P- 614. The sodium bisulfite was Mallinckrodt [19] A. Murray, Chemical retouching, The I ational Lit hog analytical reagen L grade. ra pher 36, No. 11,29 (1929). [20] L. P . Cler c, Photography t heory and practice, p . 303 (Pitman Publishing Corp., New York, N.Y., 1954). 9 . References [21] K . Hickman a nd W . Weyerts, Optical intensifi cation, Brit. J . Photo 80, 482 (1933) . [1] J . I-I. Reindorp, A co ntribution to the chemistry of [22] J . 1. Crabtree and J . F . Ross, A method of testing for residual imagcs, Brit. J . Phot o 82,244 (1935). the presence of t hiosulfate in motion picture film, J . [2] L. P . Clerc, Photography t heory and practice, p. 298 Soc. Mot ion Picture Engrs. 14, 419- 426 (1930). (Pitma n Publishing Corp., New York, N.Y., 1954). [23] I-I. D. Russell a nd J . 1. Crabtree, The reducing action [3] C. E . Ie Mees, The theory of the photographic process, of fixing baths on t he silver image, J. Soc. Motion p. 715 (The Macmillan Co., K ew York, N.Y., 1954). Picture Engrs. 18, 371 (1932). [4] Ie C. D . Hickman and D . A. Spencer, The washing of negatives and prints, Brit. J . Photo 69, 387 (1922). [5] Dr. Liippo-Cramer, Zur konstitution del' negativsubstanz Photographische Korrespondenz 49, 121 (1912). W ASHINGTON, D.C. (Paper 6401- 26)
73 530231- 60--6