. A photo.graphic s!h:er im~ge is m ade ,Permanent (fix ed) aft~r development by bathing It 111 a solutIOn contall1lng thIOsulfate whICh forms a soluble tlllosuifate complex with the res idual silver halide. Some of the sil ver in the image is sulfided by the thiosulfate durin g ~xat io~. The p~rpose of this s tudy was to d etermine the a mount of sulfiding of the silver III t he Image dunng fi xatIOn of film and paper. The amo unt of the silver reacting depends on the type of t he ligh t-sensitive layer. Also, during bleaching, the residual thiosulfate in the film or paper r eacts with silver in a potassium dichromate-s ulfuric acid bleach bath to form silver sulfide. For one p ap er , it was shown that the amo unt 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 t he reduction of silver s ulfid e in an e mulsion layer to silver so t hat the silver sulfid e may be determined in terms of the optical density of the s ilv l' dep osit. The use of hypo eliminators was investigated an d a test procedure was found for testing the effectiveness of hypo eliminators. A smaH amoun t of potassium iodide added to t he fi xing bath was found effec t iv e in preventing mos t of the s ulfidin g of the silver image during fi xation.
Oxidiz in g and re du cin g agents ge ne rated b y paper ca rto ns durin g s torage ma y react with th e im age s ilv e r to form ble mi s hes . Th e t ype of fixing ba th , co nce ntration of chl orin e in th e was h wat e r, wa s hin g tim e a nd co mpos iti o n of th e s to ra ge ca rt o ns c an be fac to rs th at acce le rate o r re ta rd th e a tta c k of th e perox ide o n th e im age s ilv er. Mi c rofi lm was he d afte r fixati o n in dist ill e d wat er o r c hl ori nefree ta p wa te r form ed bl e mi shes wh e n e xpo sed to pe roxide pa pe r. A trace of s ilv e r c hlorid e in th e im age s ilve r of processed mi c rofilm a ugme nt ed th e formation of th e na tura l type bl e mi s hes wh e n e xposed to pe rox id e paper, but hi gh conce ntratio ns of res id ual s ilver c hlorid e inhibited bl e mi s h formation. Durin g sto rage, so me s torage ca rt o ns e vo lved forma ld e hyd e, formic ac id , and a mmonia whi c h c re at e d a c h e mi cal e nviro nm ent favorabl e fo r bl e mi s h formation in mi crofilm in th e prese nce of pe rox ide . A corre lation wa s fo und be tw ee n th e in c ide nce of bl e mi s hes and th e brand of paper sto rage ca rto ns. A procedurLwas de ve loped for tes tin g proc essed mi crofi lm to d ete rmin e its s usce ptibility to blemish formation. According to the present theory , pe roxid e reac ts with the silver in th e im age, form in g col lo idal s il ver whi c h imparts a yellowi s h or reddi s h co lo r to th e b le mi s hes.Key W o rds: Archival reco rd film , bl e mi s hes du e to a ging, co lloidal silve r , mic rofi lm , mi crofi lm storage ca rton s, pe rm ane nt record film , pe roxid es.
The concentration of residual thiosulfate (hypo) in processed microfilm and its variation with storage humidity were m eas ured. The initial thiosulfate concentration varied linearly with the image density up to a density of about 2. Th e rate of decomposit ion of the thiosulfate increased as the relat ive humidity increased. The concentration of thiosulfate in a silver-free area remained co nstant for nine months in film stored at 14-percent relative humidity but began to decrease within two weeks at 88-percent relative humidi ty_ The residu al t hiosulfate in p rocessed microfilm reacted with the silver in the image to form sil ver sulfid e and the amo unt of sulfiding dming agin g at 88-percent relative humidity was mea sured . The residu a l th iosulfate concentration in microfilm was found to vary linearly with the sil ve r con ce nt ration in the fi xing bath . Potassium bromide, potassium iodide, :llld sodium chloride reacted with the res idual silver thiosulfate com plex m aking the t hiosulfate soluble. Potassium bromide and iodide effected the complete el imination of thiosulfate.
The Crabtr ee-Ross procedu re, employing t he reaction of thios ulfate with mercuric chloride to form a t urbid solution is the usual test for r esidual t hi osulfate in processed film . Quali tative test s sho\\"ed that in th is procedure part of the prec ipitate remains in t he gelat i n layer of the fi lm, caus ing the re porte d concentration of th iosulfate to be too low. When residua l th iosulfate \ms measu red in the presence of image silver , th e image silver cont ributed an add itional compon ent to the turbidity. A new test procedure \vas de veloped whi ch a lso e mploys m ercu ri c ch lo rid e as the precip itant but which reveals 2 to 3 times as much r esidual thiosulfate a s does the Crabtree-Ross procedure. R esidual silve r causes the format ion of addit ional t urbidity which is determin ed a s residual thiosulfate. A t race of ge latin is di ssolved from thc fi lm durin g the t hiosu lfate tes t, the a moun t dep endin g on fi lm ty pe. The t r ace of ge lat in had a pronounced e ffect o n t he a mount of t urbidity. The a ddit ion of a knO\l"ll amount of ge latin to t he t es t solu tion masked t he e ffect of d issolve d ge latin , makin g it possible to prepa re one calibration cur ve for a ll types of film. A new method of measurin g the res idual silver in pr oce~sed film was deve loped. A photoelectri c ne phe lometer \ms use d to mea sure the t urbidity.
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