The Effect of environment on latent image formation and stability

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4-1-1995

The Effect of environment on latent image

formation and stability

Sean O'Toole

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The Effect of Environment on Latent Image Formation and Stability

Sean W. P. O'Toole

B. S. State University College at Brockport, Brockport, New York

(1975)

A thesis submitted in partial fulfillment of the requirements for the degree of Master of

Science in the Center for Imaging Science, Rochester Institute of Technology.

April,1995

Signature of the Author: _

Accepted by:

Dana G. Marsh

Center for Imaging Science

Rochester Institute of Technology

Rochester, New York

CERTIFICATE OF APPROVAL

M. S. DEGREE THESIS

The M. S. degree thesis of Sean W. P. OToole

has been examined and approved by the thesis committeeas

satisfactory for the thesis requirement for the Master of Science degree.

Prof. RichardK.Hailstone, Thesis Advisor

Dr.Judith M.Harbison

Dr. RobertA. Curtis

Thesis Release Permission Form

Rochester Institute of Technology

Center for Imaging Science

Title of Thesis: The Effect of Environment on Latent Image Formation and

Sta bility

I, Sean William Padraic OToole, hereby grant pennission to the Wallace Memorial Library

of R. 1. T. to reproduce this thesis in whole or in pan. Any reproduction will not be for

commercial use or profit.

Signature: . _

The Effect of _Environment on Latent Image Formation and Stability.

Sean W. P. O'Toole

Submittedto theCenter for_ImagingScienceinpartialfulfillmentoftherequirementsfor

thedegreeofMasterof_Science,RochesterInstituteofTechnology.

Abstract:

Thisthesisuses an unsensitized emulsionandtwo_chemicallysensitized emulsionsto

investigatetheeffectof oxygenandwater vaporonlatent-image formationand stability. At

exposuretimes thatcauselittleor no_{low-intensityreciprocityfailure,}vacuumtreatmentof

an emulsioncanresultinphotographicspeeds_{significantly lower}thanthosefound ina

humidifiedenvironment. This_{is presumably due}tocompetitionbetween internal

desensitization sites and surfaceelectrontrapsforconduction-band electrons. Storageof a

latentimageinahumidifiedairenvironmentwillinducea speedlossinsome emulsions.

Theunsensitizedemulsionwasmost sensitivetoenvironmentalfactorswhilethe

sulfur-plus-gold-sensitizedemulsionwas not. Thisis presumably dueto thecomposition and size

ofthelatent image. Maximumchangesinphotographic speed overtimerequirethe

presence ofbothoxygen andwatervapor. Oxygenalone_maycauselatent-image_decayin

some emulsions. Watervaporinanitrogenenvironmentdidnot affectlatent-image

stability. Extended developmentand goldlatensificationrestored some ofthespeedloss

observedwiththeunsensitizedemulsion. Theunrecoveredspeedloss is duetoeither

latent-imagecenters_{beingcompletely}oxidized,or_beingtoosmalltorespondtochemical

Acknowledgments

Theauthor wouldliketoextendhis appreciation andthanks toProfessor Richard K.

Hailstone,histhesisadvisor. _{This study}would nothave beenpossiblewithouthis

patience,knowledge,and guidance.

Theauthor wouldliketoextendhis appreciationto_{GaryDiFrancisco for precipitating}and

sensitizingtheemulsionsusedinthisthesis, and_{for ensuring}that therewas alwaysan

ample _supplyof_{processing chemistry}and other consumables.

Theauthorwouldalsoliketoextendhis appreciationtoDr. Judith M. Harbisonofthe

Eastman Kodak Company. Herguidance and encouragementhave beena great asset and

theauthoris_verygratefulfor her timeand patience.

Aspecialthankyouis due Dr. Robert A. CurtisoftheEastman Kodak Company. Dr.

Curtishas beenmentor,advocatus_diaboli, a source of_{encouragement,}and afriend.

Withouthis support,thiswork would nothave beenpossible.

Lastly,Iwouldliketoextend_myappreciationto the_manyscientists andtechnical staff

Dedication.

Overthepastfiveyears, therehasbeenoneperson_{waiting patiently}onthe "widow's walk;"

waiting for herhusbandtocomehome. She has beensteadfastin hersupport and encouragement. I lookforwardto_becomingwellacquaintedwithheragain. Therefore,I dedicatethisthesis to_mywifeandbestfriend,Laura Louise Viscome-O'Toole.

"Hi, Elizabeth, it'sDaddy. Tell_MommythatI'mon_{my way}

home."

Table of Contents

List of Tables v

List of Figures vii

I. Introduction 1

II. Previous Investigations 2

III. Experimental Procedure 10

3.1 Emulsion 10

3.2 Sensitometer 10

3.3 Environments 11

3.4 Latent Image Hold Times 12

3.5 _Processing 13

3.6 Gold Latensification 14

3.7 _Sensitometry 14

3.8 Data Presentation 14

IV. Results 15

4.1 Photographic Responseat0.5 h Between_Exposingand_Processing 15

4.2 Changes in Photographic Speed Over 72 hofLatent-Image Hold Time 18

4.3 _RecoveryofSubdevelopable Latent Images ThroughChangesin Minimum

Developable Size 23

V. Discussion 26

5.1 InitialPhotographic Speedat0.5h Between_Exposingand_Processing 26

5.2 Latent-Image_StabilityOver 72 hof Latent-Image Hold Time 29

VI. Conclusions 34

VII. Future Work 35

References 37

Appendix 41

List of Tables in Text

TableI.

Table II.

TableHI.

TableIV.

Table V.

Table VI.

Table VII.

Table VIII,

ChangeinSpeedfora0.001 sExposureat0.5 hofLatent-Image Hold.

ChangeinSpeedfora 1 sExposureat0.5hofLatent-Image Hold.

ChangesinSpeedfortheUnsensitized Emulsionat a0.001 sExposure.

ChangesinSpeedfortheUnsensitized Emulsionat a 1 sExposure.

Changesin Speed fortheSulfur-Sensitized Emulsionat a0.001 s

Exposure.

Changes in Speed fortheSulfur-SensitizedEmulsionat a 1 sExposure.

Changesin Speed fortheSulfur-Plus-Gold-SensitizedEmulsionat a0.001 s

Exposure.

Changes in SpeedfortheSulfur-Plus-Gold-Sensitized Emulsionat a 1 s

Exposure.

List of Tables in Appendix

Table DC. MeasuredSpeedat0.5 hofLatent-Image Hold Time for All

Sensitizations. 0.001 sExposure Time.

Table X. MeasuredSpeedat0.5hofLatent-Image Hold Time for All

Sensitizations. 1 sExposure Time.

Table XI. Measured Speed Values fortheUnsensitized Emulsionover72 h of

Latent-ImageHold. 0.001 sExposure Time.

Table XII. Measured Speed Values fortheUnsensitized Emulsion over72 hof

Latent-Image Hold. 1 sExposure Time.

Table XIII. Measured Speed Values fortheSulfur-SensitizedEmulsionover72 hof

Table XIV. MeasuredSpeed ValuesfortheSulfur-Sensitized Emulsionover72 hof Latent-_{Image Hold. 1 sExposure Time.}

Table XV. Measured Speed Values fortheSulfur-Plus-Gold-Sensitized Emulsion

over72hofLatent-Image Hold. 0.001 sExposure Time.

Table XVI. Measured SpeedValues fortheSulfur-Plus-Gold-Sensitized Emulsion

over72 hofLatent-Image Hold. 1 sExposure Time.

Table XVII. MeasuredSpeeds Obtained_DuringExtended Development forthe

Unsensitized Emulsionover72 hofLatent-Image Hold. 0.001 s Exposure Time.

Table XVII. MeasuredSpeeds Obtained_DuringGoldLatensificationforthe

Unsensitized Emulsionover72 hofLatent-Image Hold. 0.001 s

Exposure Time.

List of Figures

Figure 1. Environmentalsensitometer.

Figure 2. Gas humidificationsystem.

Figure 3. Relative Speed LossOver Time fortheUnsensitized Emulsion. 0.001 s

Exposure.

Figure4. RelativeSpeedLoss Over Time. Unsensitized Emulsion. 1 sExposure.

Figure 5. The Effect Of Extended Development On Relative Speed Loss.

Figure 6. The Effect Of Gold Latensification On Relative Speed Loss.

I. Introduction

Theeffect of environment on photographic materialshas beenstudiedforoveronehundred

twentyyears. Previous investigatorshave foundthatatmosphericcomponents, suchas

watervapor and_oxygen,can affectthephotographicspeed anddevelopabledensityofa

silverhalideemulsion. Most investigators haveusedexposure timesoftens to thousands

ofsecondsto _studytheeffect of environmentona multitudeof emulsions. Extended

exposuretimesare usedtomaximizethesignal-to-noiseratio,but_theycan also cause a

significant amountof_{low-intensityreciprocity failure(LIRF)}inphotographic materials.

Someworkhas beenperformedtoexaminethe_{relationship between}environmentand

latent-image stabilityovertime. Difficultiesassociatedwiththis typeof_{study have limited}

thescope oftheseinvestigations. Examplesofthesedifficultiesincludepre-_andpost

exposure_conditioningofthe testemulsions andthe_handlingof materialsina reproducible

manner.

Thepurposeofthis_studywastoinvestigate howoxygen andwater vaporcan affect

photographic materials_usinganexposuretime thatcauses minimalLIRF. Theeffectsof

oxygenandwater vaporweredetermined_{byobserving latent-image stability}andinitial

photographic speedin several environments. Anunsensitized andtwo_chemically

sensitizedemulsions were usedtoobservetheeffectofchemical sensitization on

latent-image formationandstability.

A summaryofseveralpreviousinvestigations concerningtheeffect of oxygen andwater

vapor on latent-image formationand_stabilityispresentedinthenext sectionofthis thesis.

Theexperimental section will outline themethodology. Resultswillthenbepresented.

pointandgraphs of severalphenomena. The importanceofchemical sensitization relative

tolatent-image formationand_stabilitywillbe discussed. _Also, thephotographic speed

advantagethatvacuum-treatedmaterials areknowntohaveover materials conditionedto room air willbe showntobesensitivetoexposure_{time, length}ofpre-exposure

conditioning,and chemical sensitization. Tablesofthemeasuredphotographicdataare

presentedintheappendix.

II. Previous Investigations

The_followingparagraphs outline several selectedinvestigationsrelevantto this thesis. The

TheoryofthePhotographicProcess,edited_byT. H.James,isan additionalreferencefor

manyofthe topicsdiscussed inthis section.1

In _1872,Lt.Col.Wortley2

wroteto the_{British Journal ofPhotographyconcerning}

photographic sensitivity. In hisletter,_Wortleystatesthathetreatedhisphotographic plates

to"acouple ofhoursof_strong heat"

andthat thisincreasedthespeedofhisemulsion. He

goesontostatethat thisincrease inspeedwaslostafterthreedays.

TheeditorsoftheJournalstudiedthephotographic plates_Wortleysentwithhis letterand

notedthat thecolonel was_{reporting fromNaples,}Italy. Theeditors3

suggestedthathewas

observingtheeffectof relative_humidityonhisphotographic plates. _Naples,beinga

Mediterraneancoastalcity,hasanelevated relative_humiditydue_{to the warm,}seaair.

Wortley'sheattreatmentremoved atmospheric waterfromtheplates andincreasedthe

photographicspeed oftheemulsion. Afterthreedaysof_{reconditioning}to theambient

climate of_Naples, hisplateshadreturnedto their_"ordinarydegreeofhumidity"and the

Phrasessuch asthe _"ordinarydegreeof

humidity"

are not aquantitativemeasure or

descriptionof an emulsion's moisture content. _{A brief discussion concerning}the

relationship betweenmoisture content and atmospheric relative_humidity (%_RH)is

worthwhile.

ColtonandWiegand4reportedthat themoisture content responsetoaparticularrelative

humidityisuniqueto thatmaterial. Themore gelatinpresent,thehigherthemoisture

contentwillbeat_anygiven relativehumidity. At 0%_RH,themoisturecontentofagelatin

layer is approximatelyzero. Itshouldbenotedthatwatermolecules_maystill bepresent,

but hydrogen bondedto the gelatin. This hydrogen_{bondingmay inhibit}theremoval of

water. A roughly linear relationshipexistsbetweenmoisturecontent andrelative_humidity

from 20%to60% RH. Inthis region,alargechangeinrelative_humidityisrequiredto

significantlychangethemoisture contentofafilm. Above60%RH,moisture contentrises

inan almostexponentialfashion.

Anabsolutemoisturecontentvalueismeaninglessoutside of aparticular

gelatin-emulsion-support combination. _Therefore,relative_humidityisusedto_{qualitatively describe}the

moisture content of an emulsion. Relative humidities between 20% and60%are

considerednormalconditions. _Increasingtherelative_humidityabove60%willgenerate a

highmoisture content. Photographic filmlayersinthismoisture content range aresoft,

plastic,andlongerin dimension. Atrelativehumidities below_20%,thelowmoisture

contentwill resultina_hard, brittle film layerthatisshorterin dimension.

SheppardandGraham5investigatedtheeffectof_{pH, pAg,} andwater_(moisture)content on

photographicspeed. _Theyfoundthatspeeds wereat a maximum whentheemulsion was

throughout theseveral pH and_pAgregimes_theystudied. _{Peak sensitivity}wasfoundat about20% RH.

Vanselow, Quirk,andCarroll6attemptedtoisolatetheeffectsof water vaporandoxygen

onlatent-image formation._Theyusedseveral_spectrallysensitizedmotion pictureemulsions and a controlintheir study. Theirequipment was uniquebecause itallowedfor

conditioning, exposure,and_processingalltobeperformedwithinatestenvironment.

Theyusedhumidifiednitrogenandhumidifiedoxygenenvironmentstoremovethe

interaction betweenoxygenandwater.

Theseinvestigators foundthatafilmtreatedinahumidifiednitrogenenvironmentwas

usually fasterthanafilmtreatedinanoxygen environment atthesame relativehumidity.

Theirresultsalso showthatphotographic materialstreatedina20% RHenvironmentare

usually fasterthanonestreatedinan80% RHenvironmentfora given atmosphere. The

undyedcontrol materialdidnotfollow this trend.

Thechemicalsensitization oftheircontrolemulsionisnotknown. Giventhat_Vanselow,et

al.,were_studying motion pictureemulsions,it isreasonabletoassumethat thecontrol was

chemicallysensitized. Regardlessoftheexactchemicalsensitizationofthe_control,their resultsindicatethatemulsionswithdifferentspectral sensitizationswillhavedifferent responsestooxygenandwater vapor.

James7_{discussed in detailtheeffects of}

pressure,moisture,and oxygen on_latent-image

formation. Pressureeffectscanbegenerated_byusinga_drygasorvacuuminemulsion

studies. A _dryenvironment will remove waterfromthegelatin matrixand causeitto contract. Asthegelatin_contracts, itcan exertpressures_upto 2000kg/sq. cm and will

deformationofthesilverhalide_grain,althoughthemechanismisnotunderstood.8 If_the

pressureis kept below~

1000 kg/sq.cm,thisdesensitizationisreversible. Atpressures

much abovethis_level,desensitizationispermanent.

Changingthemoisture and oxygen content of an emulsionlayercanaffectlatent-image

formationanditsstability. Onepossiblemechanism7

bywhich waterandoxygen_may

affectthelatent image is:

2Ag+

_1/202

(1)

It is easytoassumefrom Reaction ₍₁₎that_removingoxygenfroman emulsionlayercan

increasethe_stabilityofthelatentimage. Jamesnotes,however, thatnotall emulsionlayers

are sensitivetooxygen. Hereportsthatpreviousinvestigatorsare almost_evenlysplit

regardingtheeffect of oxygen onlatent-image formationanditsstability. It isimportantto

notethat theseotherinvestigatorsuseda_varietyof emulsionsthatwere_chemicallyand/or

spectrallysensitized. General statementsabouttheeffect ofoxygenaredifficulttoextract

fromtheirdata.

Water mayhavebothaphysicalanda chemical rolein latent-image formationand stability.

Onesuchchemicalroleispresentedin Reaction₍₁₎above. Thephysicalrole of water_may

betoswellthegelatin matrix. Swollengelatinexerts almost no pressureonthesurfaceofa

silverhalidegrain,preventing anypressure-induceddesensitization from occurring.7

Swollengelatinisalsomore permeablethandriedgelatin. Themore permeablethematrix

is, theeasierit is foroxygenandwater vaportoreachthegrain surface.

James7_{investigatedtheeffect ofexposuretimeon}

photographic speed at a particulartime

and usedexposuretimes ofIO"2to IO4 s. Exposures werebalancedsothat_{approximately}

thesamenumberof photonswere_strikingthe testemulsion regardlessofexposuretime.

Theseexposures were performedina_varietyof environments. Fora IO4s exposure, he

foundthatvacuum-_{treatedmaterials were1.5}

logE fasterthan thoseconditionedto40% RHroom air. Atan exposure timeofafewsecondsto IO"2s,therewas_{very little}

differencebetweenmaterials_receivingavacuumor room airtreatment. Thisresult would

suggest_{low-intensityreciprocity failure}as anotherfactor forconsiderationin latent-image

stability.

ArmisteadandGalimba9wereinterested inthe_{latent-image stability}of_commercially

available,high-resolution_{low-sensitivity}photographic materials. Thesematerials are

usefulfor making hologramsandfor_trackingnuclearparticles. _TheychosethreeKODAK

materialsfor study because_they spanned afactorof1000 ingrain size and afactorof3200

inphotographic speed. Thematerials chosen wereKODAK_SO-343,finegrainpositive,

and commercialfilms. Thesamplesweregiven a 10"4s exposurethrougha_15-step

densitytablet to generate_density-logrelative exposure _(D-logE)curves.

Aftertwomonths ofstorage between exposingand_processingunder room air_conditions,

the SO-343film lostover70%ofits_densityabovebasefog. The finegrain positivefilm

lost 15%ofits_densityabovebase fog. Thecommercialfilm lost lessthan 10%ofits initial

densityintheupperscale regions ofthe_D-logEcurves.

Material_{handlingtechniques,}suchas_exposingtheSO-343filmsamplesinambient air and

then _subjectingthemtovacuumtreatment,raisesome concerns. _{Nevertheless,the}vacuum

treatmentresultedinnolossoflatent-image forSO-343 film samples. Treatmentin_dry

oxygenproduceda speedlossgreaterthan thatseen underroom-airconditions. Armistead

Platzer10_{investigated howthe}

recombination of silver andbrominecan affectlatent-image

stability. Heused a_weaklysulfur-sensitized emulsion ashistestmaterial. Sampleswere

given aIO"3s exposurethrougha_steptablet. Thetestenvironments were: 25% RHair,

0% RHnitrogen,and-100% RHnitrogen.

Hismaterials were conditionedthrougha unique process. Thesamples_initiallyreceived

treatmentinavacuumtoremove air andwater vaporfromthefilmsamples. Afterthis

treatment, the testenvironment wasthenintroduced intothevacuumchamber. Thetest

materialsthenreceivedtwohoursof_{conditioning in}thisnewenvironment. Sampleswere

thenexposed andheld ineitherthe testenvironmentorwere subjected to adifferent

environment_immediatelyafter exposure.

Platzer foundthat the_onlyconditionsthatresultedina stablelatent-imagewere a_dry

nitrogenpre-exposure_conditioningwith_dryorhumidifiednitrogen post-exposure

conditioning,andhumidifiedairpre-exposure_conditioningfollowed_{by immediately}

submergingthesamplesin degassedwater untilprocessing. _Usingthesame_conditioning

technique,heconditionedfilmsamplestoindividualmajor atmospheric componentstosee

ifone ofthegasesinduceda_densityloss. Sincethe_drygasesdidnotinducea_density

loss,Platzerconcludedthatwateristhemaincause oflatent-image loss.

Hepostulateda series of reactionsbetweenwaterandbromine_(Br2)toformhypo-bromate

(HBr03). Hypo-bromatecanthenionizetoform hydrogen and abromate ion. The

bromate ionisstableingelatinandcantravel_longdistancesthrough thematrix. Bromate

alsohasthecorrectelectrochemical potentialtooxidize silverto silverbromide. Platzer

suggestedthatbromatecan_{be particularly}effectiveat_inducingalatent-imagelossbecause

Therearetwopotentialproblemswiththeseexperiments. Oneconcern isthemethod used

tocondition samplestovarious environments. Previousinvestigators7_haveuseda 16-hr

pre-exposuretreatment_time,without_evacuation,tocondition materialstoaparticular

environment. Two hoursofpost-vacuum_{conditioning in}the testenvironment_maynotbe

sufficienttimeforthefilmtoreachequilibriumwiththe testenvironment. Thereisalso the

possibilitythat theinitialvacuumtreatment_{may beinducing}pressuredesensitization and

confoundinghisresults.

A second problemwiththis_{study is}theconclusionthatwateristhe_primaryagentfor

latent-image_{decay. This is contradictory}tohisobservationthatsamples storedin

humidifiednitrogenorsubmergedin degassedwater until_{processing have}a stablelatent

image. Ifwateristhe_primaryagent,then these treatmentsshouldhaveresultedina

significantlossoflatent image.

Kuge,Fujiwara,andHada11investigateda process_indicatingthat thereisatime_delayin

theformationof alatent image. Asilverbromidecubic emulsion was precipitated and

coatedina mono-grainlayerformat. Thisformat is exceptionally thinso that theemulsion

grains _layside-by-sideonthesupport. Theadvantageofthisformatis that_{it is very}

convenientfor counting developed latent-imagesitesonsilverhalidegrains. The

disadvantageis that thereis littleoptical_densityavailableinthis_{format. The only way}to

obtain usefuldata istocountlatent-imagesiteson silverhalidegrains. Sampleswere

conditionedinavacuum environmentfor 16 h beforeexposure. Aftera 1.5*10"6s

exposure, sampleswerestoredinthevacuumfor up to20min_{before development.}

Kuge,etal.,founda50%increase inthenumber of_{developable latent-image} sites after 10min

of post-exposure vacuumtreatment. This increase isseen at amid-_{scale point on}

developable-centerversus_logrelative-exposurecurves. _Introducingroom airintothevacuum

chamber stopsallfurtherincreasein developable latent-imagesites.

KugeandFujiwara12continuedthiswork_usingvarious environments. Theconditions

theyexperimentedwithwere_dryairat 1 to30torr,dryair atnormalpressure,-100% RH

nitrogen,66% RHair, andvacuumas a reference check.

To varyingdegrees, theincrease inthenumber ofdevelopable latent imageswithstorage

timewas observedinallbutthe66% RHroom airenvironment. Theinvestigatorsattribute

thisincrease in developable latent imagestomobilesinglesilver atomspecies_combining

withsubdevelopablelatent images. Sinceanincrease inthenumber ofdevelopablecenters

was observedinthesaturatednitrogenenvironment,theinvestigatorsbelievethatoxygenis

the_{primary factor for stopping}thisgrowth process. _{One way}thatoxygen couldinhibit

thisgrowth processistoact asanelectron_trapand recombination center.

02+

e -02"

(2)

02~

III. Experimental

3.1 Emulsion. A0.45 mAgBroctahedral emulsion was precipitated in gelatin. A

sample ofthisemulsion was sulfur sensitized_{using 1.33 mg} sodium_{thiosulfate/Ag}mole.

Asecond sample was sulfur-plus-gold sensitized_using thesame sodiumthiosulfatelevel

plustheaddition of_{2.00 mg}potassium_{chloroaurate/Ag}mole. Theselevelsofchemical

sensitizers are_historicallyknowntoprovide nearoptimumsensitization conditionsforthis

emulsion.14

The unsensitized,sulfur-,andthesulfur-plus-gold-sensitized emulsions were coatedon a

clear acetate support at _{100 mg Ag/sq. ft.}withahardenedgelatin overcoat. Theemulsion

meltswereadjustedtopH5.5 and_{vAg 90}mV at40C beforecoating. Materialswerecut

into 12 inch_by35mmfilmstripsforease ofhandling.

3.2 Sensitometer. Pre- _{and post-exposure}

conditioningofthe filmsamples wasdone

usingan environmentalsensitometer. This deviceisa modificationofthestainless steel

belljarused_byJames, etal.7-15 _One

modificationistheincorporationof a0to 3.0 density, 15-steptabletintotheexposure window. Eighteen film_samples,in six groups of

three,canbe_{conditioned, exposed,}and storedina controlled environmentuntil

processing. Figure 1isa sketch oftheenvironmental sensitometer.

Valved Gas Exhaust

f

FilmSamples

CirculationFan

GasInputorVacuum Draw

Exposure Window

with_StepTablet.

EG&G Light Source

J

Pedestalrotates sampleswithout_breakingenvironmentalseal.

Italso places samplesflushagainstthe_step tablet.

Figure 1. Environmental sensitometer.

Exposuretimesof0.001 and1 s were usedtoinvestigatethephotographic responseofthe

testemulsionsin a regimewherethereisminimal orno_reciprocityfailure. Thelightsource

forthe0.001 s exposure was anEG&G Mark VIIsensitometer. The EG&G sensitometer

wasplaced sothatits lightsource was perpendicularto theexposurewindowofthe

environmental sensitometer. Awater-cooledquartz-halogen_lampwas usedforthe 1 s

exposure.

3.3 Environments. Seven differentenvironments were chosen for studyatthe 0.001 s

exposuretime. _They were0% RHvacuum,air,andnitrogen; 20% RHairand_nitrogen;

and80% RHairandnitrogen. Environments wererestrictedto0% RHvacuum, air,and

nitrogen; 20% RHairandnitrogenforexperiments_usinga 1 s exposuretime.

Materialswere conditionedin atestenvironmentfor 72 h beforethestart of an experiment.

Avacuum of0.05 torrwas generated_byamechanical_pumpwitha molecular sieve_trapto

minimize oilback streaming. Nitrogenwas supplied_{usingcommercially}available

compressed gas cylinders. Airflowwas provided_bythe_buildingair supply. A

pretiminary studywasdonetocomparethe_buildingair_supply toacompressedair

cylinder. Nodifferences_{in sensitometry} werefound.

Relative_humiditywas controlled_{by bubbling}the testgasthroughdistilledwater,cooling it

to thedesiredwetbulbtemperature_usingawater/glycol_bath,and then_allowingthegasto

equilibrate toroomtemperaturebefore its introduction intotheenvironmental sensitometer.

Relative_humiditywas checked_usingahand heldtemperature/relative_humidityprobe

placedinthegas effluentofthesensitometer. Figure 2 is a schematicofthe_humidity

control system.

Gas Output

Controlled Temperature Water/Glycol Bath Distilled Water

Figure 2. Gas humidification system.

3.4 Latent-Image Hold Times. Six different times _{between exposing} and _processing

were chosen to_{study latent-image} stability. _Theywere_{72, 48, 24, 4, 1,}and 0.5 hof_delay

between_exposingandprocessing. Thissequence oftimes between exposingand

processingisreferredtoaslatent-image hold timesorasthelatent-imageholdtimeprofile.

Itwas not possible togeneratelatent-image holdtimesshorterthan0.5h due to the time

requiredtounsealtheenvironmental_{sensitometer,}removethe samples,and transport them

to the_{processing laboratory.}

Anerror of 2s was allowedbetweenthescheduled and actualexposuretime_duringthe

last four hoursofthelatent-imageholdtimeprofile. Anerror of 15 min wasallowedfor

the_{24, 48,} and72 h exposurepoints.

3.5 Processing. _{Fresh, commercially} available_{processing chemistry} was used.

KODAK D-19 DeveloperandKODAKFixerwere madewithin72hof scheduled

processing. Filmsamplesweredeveloped for6min; immersedina_{stop bath for 30}s;

fixed for 5.5 min;andwashedfor 5 min. A2 sburstofnitrogen was used_{every 7} sto

agitateallthe_processingchemistry. AWing-Lynchtemperaturecontrollerwas usedto

maintain a20C_processingtemperature. Afterwashing, thesamples were placedina

forced-air_dryingovenfor 30 min.

Sixminutes of_{processing in KODAK D-19 Developer}appearsto_developfive-atomand

largersilvercenters.16'17 _After48

min of_{development,approximately} 10%ofthe three-atomsilvercenterswillinitiate_development,whereaslargermetal clusterswillhavea

100% probabilityof_initiatingdevelopment. A latentimage_{incorporating}goldwillbe

developableafter 12minof_{processing if}thereare atleastthreemetalatomsinthecluster.

Theoptimummethod of_processingwouldbetoprocessall 18 samplestogetherinthe

sametankofdeveloper. Thisprocedure wouldalso require a controlled-temperature

processingtank thatwas severaltimeslargerthan whatwas available. The best alternative

wastoprocesseach sensitization typeindividually.

Itwas not_physicallypossibletoplacethreesets ofsamplesintothreeseparate_processing

tankssimultaneously. Tocompensate_{for this,}the_processingoftheunsensitizedand

sulfur-plus-gold-sensitized emulsion samples were offset_by 10saroundthedesired

processingtime. Thesulfur-sensitized materials were processedat0.5hafterthelast

exposure. Theunsensitized emulsion sampleswereplacedinthedeveloper 10sbeforethe

sulfur-sensitized emulsion samples. Thesulfur-plus-gold-sensitized materials were placed

in processing chemistry 10saftersulfur-sensitizedmaterials. Errorin processingtimewas

estimatedtobe 1 s.

3.6 Gold Latensification. Goldlatensification was performed on samples ofthe

unsensitized emulsion. Materialswere placedina gold bathasdescribed_byJames,

Vanselow, andQuirk18 for 10min andthen submergedfor 5minutesina 1 gpotassium

bromide/Lsolution. _{Immediately following}thepotassiumbromide bath,materials were

processed_usingtheproceduredescribed insection3.5.

3.7 Sensitometry. Film densities were measured_using anX-rite densitometer.

Thesedensitieswerethen transferredtoacomputerthatcalculated photographic speeddata.

Thepoint usedforcomparison inthis thesisisphotographic speed atbase_fogplus0.50

densityunits(speedatD-min+0.50). Thispointis approximatelymid-scale onthe

density-logrelative exposure _(D-logE)curvesforallthematerials examined.

3.8 Data Presentation. Tables and graphs ofthe measureddata are presented

throughoutthisreport. Alldataarepresentedinunits of_logrelative exposure_(logE).

Giventhesame_densityvalue,amaterial withalarge_logEvalueis photographicallyslower

than amaterial with asmall_logEvalue. Thisresultis dueto thefirstmaterial_requiring

morelighttoachievethedesired_densitythanthesecond material.

Tablesandgraphs ofspeed change are usedtosummarizethedata. Change in speedover

timeusesthe0.5h datumasthereference pointfora givenenvironment. The_remaining

fivepoints ofthelatent-image hold timeprofile are comparedto thispoint. Therelative

effect ofenvironmentoninitialphotographic speedwillusethevacuum-treatedmaterialsas

thereference point. Speed losseswillresultinnegativevaluesandspeed gainswillhavea

positive value. Thereference pointforthese tablesand graphswillhavea value ofzero.

Availabledata19 _suggeststhat

atwostandarddeviationvalue of0.04_logE isa reasonable

estimate ofthe_{uncertainty in}themeasured speed. _{Thus,statistically}meaningfuldifferences

are_{found only}whendatapointsare separated_byatleast0.06_logE.

IV. Results

4.1. Photographic Response at 0.5 h Between _Exposing and Processing.

Tables IandIIpresentthechangeinspeeddataobtainedfor bothexposuretimes and all

three sensitizations. In_general,therewasno significantdifference inspeedbetween

samplestreatedin humidifiedair andhumidifiednitrogen. Unsensitizedemulsion samples

treatedin20%RHnitrogen were0.10_logEfasterthan those treatedin 80%RHair. This

differencewas observed at an exposuretimeof0.001 s.

Thevacuum-treatedmaterials wereslowerthanmaterialstreatedinahumidified

environmentfor bothexposuretimes. Unsensitizedemulsionsamples_receivinga 1 s

exposurehad only halfthespeeddifference observed at a0.001 s exposure. The

unsensitizedemulsion was the_onlymaterialthatwassensitivetoexposure timeinthis

regard. This sensitivity may be duetotheonsetof_{low-intensityreciprocity}failure when

using a 1 sexposure with thisemulsion.

Sensitizationtypedidaffectthespeeddifferencebetweenthevacuumandthehumidified

environmenttreatments. Theunsensitizedemulsionhadadifferenceof0.29to0.39 _logE

betweenthesetreatmentsat a0.001 s exposure. Thisspeeddifferencewasreducedtoa

range of0.15to 0.20_logEatthe 1 s exposure. Thesulfur-plus-gold-sensitizedemulsion

hada speeddifferenceof0.13 to0.19_logE. Thesulfur-sensitizedemulsionhadthe

smallestdifference in speedbetweenvacuumandhumidifiedenvironments with valuesof

0.05 to0.10_logE.

Themeasured speed values at0.5hoflatent-imagehold forallthreesensitizations are

presentedin Tables IXandXoftheappendix.

able I. Change in Speed for a 0.001 s Exposure and at 0.5 h of

Latent-nage Hold.

Delta Speed(logE)RelativetoVacuum.

Environment Unsensitized Sulfur Sensitized Sulfur-Plus-Gold Sensitized

Vacuum 0 0 0

0%RH_{N2 0.10} -0.07 -0.09

0%RH Air 0.13 0.02 -0.07

20%RH_{N2 0.39 0.10 0.17}

20%RH Air 0.34 0.09 0.14

80%RH_{N2 0.35 0.07 0.17}

80%RH Air 0.29 0.05 0.13

able II. Change in Speed for a 1 s Exposure and at 0.5 h of Latent-Image

[old.

DeltaSpeed_{(log E)}RelativetoVacuum.

Environment Unsensitized Sulfur Sensitized Sulfur-Plus-Gold Sensitized

Vacuum 0 0 0

0%RH_{N2 0.12} 0.07 0.16

0%RH Air 0.15 0.06 0.17

20%RH_N2 0.20 0.08 0.19

20%RH Air 0.15 0.06 0.17

4.2. Changes in Photographic Speed Over 72 h of Latent-Image Hold

Time.

Theunsensitized emulsionhadthegreatestlossoflatentimageoverthe72htestperiod.

TablesIIIandIVindicatethata speedlossof0.18 _logEwas observedinsamplestreated

ina20% RHair environment atbothexposuretimes. Thespeedlossat80% RHwas not

statisticallydifferent fromthe20% RHairtreatmentatthe0.001 s exposuretime. Aspeed

losswasobservedin0%RHair at a 1 s exposuretime. Thespeedlossobservedatthe

0.001 s exposurein 0% RHair was not_{statistically}significant. Treatmentofmaterialsin

thevacuum andnitrogenenvironments resultedina stablelatentimage. Changes inspeed

fortheunsensitized emulsionareshownin Figures3and4.

Thechangein speeddata forthe_chemicallysensitized emulsions are presentedin Tables V

throughVDI. Withtwo_exceptions,chemical sensitization resultedina stablelatentimage

forallenvironments studied. The firstexceptionis forthesulfur-sensitizedemulsion

samples treatedin humidifiedair. Ata0.001 s exposure_time,a speedlossof0.06_logE

wasobserved overthefirst 24 hoflatent-image hold (Table V). Therewas no continued

fadingofthelatent imageafterthe24 hpoint.

Thesecondexceptionisa speedgain betweenthe0.5handthe 1 h latent-image holdtimes

forthesulfur-plus-gold-sensitizedemulsion. Thisgain was seen atthe0.001 s exposure

(TableVII),butnotatthe 1 s exposuretime(Table VIII). Therearedoubts whetherthis

speed gainisreal.

Themeasuredspeedsatthelatent-imagehold timesare presentedin Tables XIthroughXVI

oftheappendix.

Table III. Changes in Speed for the Unsensitized Emulsion at a 0.001 s

Exposure.

Delta Speed(log E)Relativeto the0.5 h Point

Hold Time Vacuum 0%RHAir 20%RH Air 80%RH Air 0%RHN2 20%RH_N2 80% RH_N2

0.5 h 0 0 0 0 0 0 0

lh 0.02 0.03 -0.01 -0.02 0 0 0.01

4h 0.02 0 -0.03 -0.03 0.01 0.03 0.03

24 h 0.04 -0.01 -0.12 -0.10 0.03 0.03 0.02

48 h 0.04 -0.04 -0.14 -0.12 0.03 0.03 0.03

72h 0.05 -0.04 -0.18 -0.15 0.00 0.03 0.03

Table IV. Changes in Speed for the Unsensitized Emulsion at a 1 s

Exposure.

DeltaSpeed_(logE)Relativeto the0.5hPoint.

Hold Time Vacuum 0% RH Air 20%RH Air 0%RH_{N2 20%RHN2}

0.5 h 0 0 0 0 0

1 h 0.02 -0.02 0 0 0.03

4h 0.02 -0.02 -0.05 0.02 0.04

24 h 0.02 -0.05 -0.12 0.02 0.05

48 h 0.05 -0.06 -0.15 0.03 0.06

72h 0.03 -0.09 -0.18 0.03 0.05

CHANGE IN SPEED AT D-MIN + 0.50

UNSENSITIZED EMULSION. 0.001 a EXPOSURE

12

DELTA SPEED _{(log E)}

0.05

-E

___=:;

f.

__

0.00- -i1

a. -0.06 --0.10 --A. . . o -0.15

-i i i

'

t\

1 1 1 1

24 36 46

HOURS BETWEENEXPOSINGAND PROCESSING

60 72

0% RH AIR

-*-On RH N2

2055 RH AIR

20% RH N2

..Q.

80% RH AIR

80% RH N2

VACUUM

'igure 3. Relative Speed Loss Over Time fortheUnsensitized Emulsion.

CHANGE IN SPEED AT D-MIN + 0.50 UNSENSITIZED EMULSION. 1 s EXPOSURE

DELTASPEED _(logE)

0.05-

-0.00

-0.05-

--0.10

-0.15

-0.20

12

"^^

="-" S :

j

?El.

-- _A.

1

'"''[]

A-. . .

'' A-...

,

' '

n

1 1 1 1 1

24 36 48

HOURS BETWEENEXPOSINGAND PROCESSING

60 72

Q _{0% RH AIR}

"*-0% RH N2

A _{20% RH AIR}

-*-20% RH N2

VACUUM

'igure 4. Relative Speed Loss Over Time fortheUnsensitized Emulsion.

Table V. Changes in Speed for the Sulfur-Sensitized Emulsion at a 0.001 s

Exposure.

Delta Speed(loeE)Relativeto the0.5 h Point

Hold Time Vacuum 0%RH Air 20%RH Air 80%RH Air 0%RHN2 20%RH_N2 80%RH_N2

0.5 h 0 0 0 0 0 0 0

1 h 0.01 0.01 -0.01 -0.01 0.01 0 0.01

4h 0.02 -0.01 -0.03 -0.03 -0.01 0 0.01

24h 0.02 0 -0.06 -0.06 0.01 -0.01 0

48 h 0.02 -0.01 -0.06 -0.03 0.02 -0.01 -0.02

72h 0.03 0.00 -0.06 -0.05 0.03 -0.01 -0.01

Table VI. Changes in Speed for the Sulfur-Sensitized Emulsion at a 1 s

Exposure.

DeltaSpeed(log E)Relativeto the0.5 h Point.

Hold Time Vacuum 0%RH Air 20%RH Air 0%RHN2 20% RH_N2

0.5 h 0 0 0 0 0

lh 0 -0.03 -0.01 0 0

4h 0 -0.03 -0.04 0.01 0

24 h 0 -0.02 -0.04 0.01 0

48h 0.03 -0.02 -0.04 0.02 -0.01

72h 0.02 -0.02 -0.03 0.04 0

Table VII. Changes in Speed for the Sulfur-Plus-Gold-Sensitized Emulsion at a

0.001 s Exposure.

DeltaSpeed(log E)Relativeto the0.5 hPoint.

Hold Time Vacuum 0%RH Air 20%RH Air 80%RH Air 0%RHN2 20%RH_N2 80%RH_N2

0.5 h 0 0 0 0 0 0 0

lh 0.01 0.07 0.01 0.01 0.01 0 0.02

4h 0.01 0.07 0.01 0 0 0 0.01

24h 0.02 0.05 -0.01 0 0 -0.01 0

48h 0.03 0.08 -0.01 0.01 0.02 0.01 0.01

72 h 0.04 0.11 0 0.01 0.04 0 0.02

Table VIII. Changes in Speed for the Sulfur-Plus-Gold-Sensitized

Emulsion at a 1 s Exposure.

DeltaSpeed(log E)Relativeto the0.5 h Point.

Hold Time Vacuum 0% RH Air 20% RH Air 0% RH_N2 20%RH_N2

0.5 h 0 0 0 0 0

lh 0.02 -0.01 0 0 0.01

4h 0.01 0 -0.02 0.01 0.01

24 h 0.02 -0.01 -0.01 0.01 0.01

48 h 0.04 0.02 -0.01 0.03 0

72h 0.04 0 0 0.03 0.02

4.3 _Recovery of _{Subdevelopable Latent Images Through Changes in}

Minimum Developable Size. Experimentswere performed to attempt_recovery ofthe

lost latent imageintheunsensitized emulsion after72hoflatent image holdtime. The

developmenttimewasextendedtodetectsmallerlatent-imagesites. Threesets of six

unsensitized emulsion samples weretreatedina20% RHair environmentand a72h

latent-image-hold-timeprofile was performed. Developmenttimesof_{6, 24,}and48min were

used.

Adevelopment timeof6min resultedina speedlossof0.20_logEoverthe72 h holdtime

profile. Twenty-fourminutesofdevelopmentreducedthespeedlossto0. 16_logE. After

48min of_development,thespeedlosswasreducedto0.13_logE. As developmenttime

increasedfrom6to48min,D-min increased from 0.04to0.17. (Appendix,Table_XVII.)

Extended development didrecoversomeofthelatent-imagesitesthathad fadedtobelowan

Ag5center. Thisprocedure alsodevelopedsmaller_fogsitesthatwere not seen_duringa6

mindevelopment in KODAK D-19 Developer. Figure 5presentsthechangeinspeed over

72hoflatent-image hold forextendeddevelopment.

Gold latensificationwas also usedtoattempt_recoveryofthe sub-developablelatent-image

sites. Threesetsof unsensitized emulsionsampleswereconditionedina20%RHair

environmentand a72h latent-image-hold-timeprofilewasperformed. Oneset was gold

latensified usingtheprocedure oudinedinthesection3.6ofthis thesis. Asecond set was

submergedfor 15minina solution_{containing 1 g}potassiumbromide/L. This_pre-soaking

treatmentwouldaccountfor anyeffectof gelatin_swellingondevelopment. Thethirdset

waskept inroomconditions andwas not pre-soakedbefore development. Thesematerials

weredeveloped in KODAK D-19 Developer for 6min. Thespeedloss data fromthis

experimentarepresentedFigure 6.

Boththesampleskeptunder room conditions andthosepresoakedinthebromide bath

priortodevelopmentlost 0.18_logEover72 hr. Samples receivinggoldlatensification lost

0.08_logEof speed_duringthesametimeperiod. This indicatesthatatleastsomeofthe

lostspeedis duetolatent-imagesites_degradingtoa sub-developablesize. Itisnotknown

howmuchoftheresidual speedloss is duetolatent-imagesites notmadedevelopable

throughgoldlatensificationortolatent-image sites_beingdestroyed.

Themeasureddataforthelatensificationexperiments are presentedin Tables XVIIand

XVIII intheappendix.

CHANGE IN SPEED AT D-MIN + 0.50.

EXTENDED DEVELOPMENT. 0.001 a EXPOSURE.

0.05

0.00

-0.05

-0.10

-0.16

---0.20

DELTA SPEED _(logE)

12 24 36 48 60

HOURSBETWEEN EXPOSINGAND PROCESSING

6min KODAK D-19 "

A-24minKODAKD-19

--48min KODAK D-19

Figure5. The EffectofExtended DevelopmentonRelativeSpeed Loss.

CHANGE IN SPEED AT D-MIN + 0.50. GOLD LATENSIFICATION. 0.001 s EXPOSURE.

0.05

0.00

-0.05

-0.10

-0.15

---0.20

DELTA SPEED (logE)

24 36 48

HOURS BETWEEN EXPOSING ANDPROCESSING

72

GOLD LATENSIFICATION "^"

BROMIDEBATH

-O-20%RH AIR

Figure 6. TheEffectofGoldLatensificationonRelativeSpeedLoss.

V. Discussion

5.1 Initial Photographic Speed at 0.5 h Between _Exposing and Processing.

Materialstreatedina vacuum environment were_significandyslowerthan those treatedina

humidifiedair environment regardless of exposuretime. Thisis_contrarytoresults

published_{in many}other studies. Asmentioned_above,James7foundthatexposuretime

has a significant effect when_comparingphotographic speedsinvarious environments. At

longexposures of IO4s,therewassignificantdifferenceinspeedbetweenmaterials

conditionedinvacuumandroomair. Asexposuretimewasshortenedtolessthana

second,thisdifferenceinspeedbecamenegligiblein his investigation.

Longexposuretimesmaximizethedifferences inphotographic responseinduced_by

treatmentinvarious environments. _{Low-intensityreciprocity}failureoccurs atthese_long

exposuretimes. Itispossible_that,duringa_{low-intensity}exposurein humidified_air,

oxygen andwater vaporare_reactingwiththelatentimage[Reaction_(1)] and/or_causing

recombinationoftheconductionbandelectronswithholes [Reactions₍₂₎and(3)]. The

exposuretimesusedinthisthesiswere positionedforminimal_{low-intensityreciprocity}

failure basedon_previouslypublished_reciprocitycurvesforsimilaremulsions.20'21

Pre-exposure conditioningtechnique_mayalso affecttheinitialphotographic speed.

Traditionally, 16 hofpre-exposure_{conditioning has been} usedforenvironmental studies.

Babcock,etal.,13_{foundthatconventional evacuationprocedures}

maynot remove all the

oxygenfromanemulsionlayer. Oxygen andother residualmaterials caninterferewith

latent-imageformation. Inthis_thesis, thematerialsusedto _studytheinitialphotographic

speedswereconditionedforover 140 h before_they wereexposed. Thisextended

conditioningwas achieved_{byconditioning}for 72 h beforethestart ofthe experimentand

an additional 71.5 hbetweenthe startoftheexperimentand exposure at0.5 h before

processing. Onehundred_fortyhoursof pre-exposurevacuum_conditioningwill_likely

removetheadditional oxygen andwaternot removed_duringthetraditional 16 hpre

exposuretreatment.

The differencein initialphotographic speedbetweenthe treatmentinavacuumandina

humidifiedenvironmentissensitizationdependent. Theunsensitizedemulsionhadthe

largest difference inspeedbetweentreatmentinvacuumandhumidifiedenvironments. The

sulfur-plus-gold-sensitizedemulsionhada smallerdifferenceinspeedbetweenthe two

treatments. The sulfur-sensitized emulsionhadthesmallestdifference inspeed.

Electrontrapsare_{necessary for latent-image formation}andthedepthoftheelectron_trapis

sensitizationdependent.22-23 Inan unsensitizedemulsion,thesurface electrontrapsare

very shallow. Vacuumtreatment_maycreateinternaldefectsthatcan_successfullycompete

for_trappingelectrons andholes. These defectsites_{may lead}tointernallatent-image

formationorinternalrecombination,resulting in fewerelectrons_beingavailabletoforma

surfacelatent image. The latentimagesthatdo formwillbesmallerbecausesome electrons

arelostto theseinternalsites. Unsensitizedemulsion samples conditionedtoahumidified

environmentwillnothavevacuum-inducedinternal defectsites. Thisresultsin larger

surfacelatentimagesand greater speedwhencomparedwiththevacuumtreated

unsensitized emulsion.

Exposuretime_mayalsoaffectthespeeddifference betweenthevacuum andhumidified

environmenttreatmentsfortheunsensitized emulsion. Ina_{high-intensityexposure,} such

as0.001 s,anumberoflatentsub-images_{may form. These latent}sub-images_may

competewith each otherforavailable electrons. Thiscompetition willdecreasethe

probabilityof_formingadevelopablesurfacelatentimage. Latent-image_dispersityis

reducedastheexposuretimeincreases. A longerexposure should resultinfewerand

larger latentimagesas well as a greater_probabilityof_forming adevelopablesurfacelatent

image.

Thehypothesisoflatent-image_dispersityissupported_bythechangein speeddata

presentedin Tables IandII fortheunsensitized emulsionatthe0.5 h latent-image hold

point. Thematerials_receivinga0.001 s exposurehada speeddifferenceof0.39_logE

between thevacuum andthehumidifiedgastreatments. Thematerials_receivinga1 s

exposurehada speeddifferenceof0.20_logE. Areduction of_dispersityisthemostlogical

explanationforthespeed changedecreaseas exposuretime increases.

Sulfur-sensitizedemulsions also are subjecttovacuumdesensitization. However,the

sulfur sensitization sites are ableto_successfullycompetewith_anyvacuum-inducedinternal

desensitization. Thiswillreducethespeeddifference betweenexposuresinahumidified

environment andthoseinvacuum. Chemicalsensitization willdirect latent-image

formationto thesensitization sites regardless oftheenvironmental conditions. Thiseffect

issupported_bythedeltaspeeddata in Tables IandEI forthe_chemically sensitized

emulsions.

Thesulfur-plus-gold-sensitizedmaterialshaveagreaterspeeddifferencebetween

treatmentsinvacuumandthehumidifiedenvironmentsthan thesulfur-sensitized materials.

Theelectron _trapdepthforasulfur-plus-gold-sensitized emulsion is lessthan thatofa

sulfur-sensitizedemulsion.22'23 _{This difference inelectron}

trapdepthscouldindicatethat

aninternaldesensitization siteisabletocompetewithgreatersuccessforelectronsina

sulfur-plus-gold-sensitizedemulsion. _However,thiswouldcontradict_previously

publishedresults_indicatingthatlatent-imageformationina

sulfur-plus-gold-sensitized

emulsionis less _likelytobeaffected_byaninternaldesensitizationsite thanina

sulfur-sensitizedemulsion.24

Thus, wedonothavean explanationforthe greater_{desensitization}

ofthesulfur-plus-gold-sensitized emulsion thanthesulfur-sensitizedemulsion _byvacuum

treatment.

Itwouldbepossibletodetermineif internal latent imageswere_being formedas a result of

vacuumtreatment_byusingawhole-graindeveloperinsteadof a surfacedeveloper.

However,sincelatent-image _stabilitywasthe_{primary focus}ofthis_thesis,theseadditional

experiments were notdone.

5.2 Latent-Image _Stability Over 72 h of Latent-Image Hold Time.

Unsensitizedemulsionsamplestreatedineither a_dryorhumidifiednitrogen environment

donot show a speedlossover72hoflatent-image hold timewhereastreatmentinanair

environmentdoes induceaspeedloss.

The lackof a speedloss inthenitrogenenvironmentsindicatesthatnitrogendoesnot affect

the_stabilityof alatent image. The dataalsoindicatesthatwater vaporinaninert

atmospherewillnotdegradealatentimageover72 hoflatent-image hold. These

statementsare also validforthe_chemicallysensitized emulsions studiedin this thesis.

A speedlosswas observedaftertreatmentin_dryair_usinga 1 s exposure. Thereis a_trend,

not_{statistically}proven,_indicatingthat treatmentina0%RHair environment and_using a

0.001 sexposure willalso resultin a speedlossovertime. _Extendingthelengthofthe

latent-image hold timewould_verifywhethera speed_{loss actually}occurs as a result of

treatmentin0% RHair.

Observing a speedlossaftertreatmentina_dry airenvironmentdoesnot meanthatoxygen

is the_onlymaterial availabletoreactwith alatentimage. _Flowing0% RHair overthe

emulsionwill_drythegelatin. However,not allthewater willberemoved.4

Somewater

willbetrapped throughhydrogen_bondingwiththegelatinor_{may be}trapped onthegrain

surface. Waterand oxygen canthendegradethelatent image.

Therearetwopossible reactionsbetweenoxygen and alatentimage. Reaction(4)was

presentedearlier.

2_Ag+

_l/2

₀₂

+2Ag+

(4)

2_Ag+

_1/2

->H20+2Ag+ (5)

Reaction₍₅₎ isequivalenttoReaction_(4), butappropriatefortheacidic nature ofthe

coating.

Watervapor_mayparticipateinthelatent-imageoxidation process as a reactant or as a

transporterof protons. _{Evidence supporting}thesynergisticaction ofoxygen andwater

vaporisseeninthedata fortheunsensitizedemulsion. Aspeedlossof0. 18_logEis

observed aftertreatmentina20% RHair environmentfor 72 hr. Treatmentinahumidified

air environmentismuch more conducivetospeedlossthan treatmentina0%RHair

environment. Thepresence ofwaterisimportanttoobtain maximumspeedloss.

Athirdpossible_waythatwatercanparticipateinthelossoflatentimageis_byphysically

swellingthegelatin. _Swellingthegelatin willincrease the_permeabilityoftheemulsion

layer. Thiswillfacilitatetheflowof reactantstoalatent-imagesite. It isquite possiblethat

water_mayparticipateinallthreeways simultaneously.

ColtonandWiegand4have indicatedthatwateris stillpresentin adriedemulsion_layer.

Thequestioncanbeaskedwhetheroxygencandegradealatentimagewithoutthepiesence

of water. LeeandErvin25foundthatit ispossiblefora_negativelycharged gas-phase

silver clustertoreactwithoxygen.

Agn-+02->Agn02- ₍₆₎

Thisreaction_{may be}a partofthereactionsequenceshownin Reactions ₍₄₎and(5). The

reaction rate_{is approximately}tentimesgreaterforan even-sized silver clusterthanforan

odd-sized silver cluster. _Also,largersilver clusters reactfasterthansmallerclusters.

Gas-phasegold clusterswillreactwithoxygeninafashionsimilarto thatofgas-phase

silver clusters. _However,LeeandErvinfoundthat theoxidation rateforgoldclustersis

approximately tentimesslowerthantheoxidation rateforsilver clusters. Thisresultwould

suggestthata gold-incorporatedlatentimagewouldbe lesspronetooxidationthana

silver-only latent image. Theobservationsinthis thesisforthesulfur-plus-gold-sensitized

emulsions supportthishypothesis.

Theunsensitizedemulsion wasfoundtobemore susceptibletolatent-image_fadingina

humidifiedenvironmentthanthesulfur-sensitizedemulsion. Theobservations made_by

LeeandErvin mayexplainthisresult. Anunsensitizedemulsion often_{forms only}one

latent imagewhenexposedtolight. Sulfursensitizationdirects latent-imageformationto

multiple sites onthe surfaceofthesilverhalidegrain. _Assumingthat the twomaterials

havereceived exposuresthatwillresultincomparabledensitiesandthat thelatent imagesin

question arelargerthantheminimumdevelopablesize, thesinglelatent imageonthe

unsensitized emulsion grain willbelargerthanthemultiplelatent-imagesformedonthe

sulfur-sensitized emulsion grain.26 _{Computer simulationsof}latent-image formation

performed_byHailstone27 supportthis statement. Asa_result, thelarger latentimageon the

unsensitizedemulsion grain_mayhavea greater_probabilityof_beingoxidizedthanthe

smaller,multiplelatent imagesonthesulfur-sensitizedemulsion grain.

Investigationsperformedboth_byTaniand_byMatsubaraand_Levymayalsosupportthe

hypothesisthatbothsize and composition of alatent imagecan affectthepotentialfor

oxidation. Tani28investigatedtheredoxpotential ofthelatent image_bysubmerging

variouslysensitized emulsion samplesina redoxbuffer for upto65h andthen_processing

the materials. He foundthat theunsensitizedandthesulfur-sensitized emulsionsbothlost

similar amountsoflatent imagedueto treatmentinthebuffer. The

sulfur-plus-gold-sensitized emulsion was stable. Heattributesthis_stability to thehighelectronegativevalue

ofgoldinthesilver-gold centers.

MatsubaraandLevy29performed similar experiments_usingafiveminutetreatmentinthe

sametypeofredoxbuffer. _Theyalsofoundthat thesulfur-plus-gold-_{sensitized emulsion}

was stable. _However,Matsubaraand_Levyfoundthat theunsensitized emulsionlostmore

latentimageaftertreatmentintheredoxbufferthan thesulfur-sensitized emulsion. _They

suggestedthat thisobservation_may,in_part,be duetosilversulfide_beingincorporatedinto

thelatent imageof a sulfur-sensitized emulsion. Thepresence of silver sulfideinthelatent

image maychangetheoxidationcharacteristicsofthelatent image. Thisincorporation

couldexplain_why,at a5-atomminimumdevelopablesize,alatent image ina

sulfur-sensitizedemulsionismorestable than a5-atomlatent image inan unsensitized emulsion.

Both investigations may becorrect. Taniassumedthathe hadreached equilibrium after65h

oftreatment. Matsubaraand_Levy assumedthat_theywerenotinequilibrium. It ispossible

thattheunsensitized emulsionhasahigherinitialrate oflatent-imageoxidationthan the

sulfur-sensitized emulsion. Onceequilibrium isreachedin theredox_{buffer,the unsensitized}

andsulfur-sensitized emulsions have similarlossoflatent image. Thedifferencein

image lossratesbetween theunsensitized andthesulfur-sensitizedemulsionsinhumidified

air_maysupportMatsubaraandLevy'sobservations. _Extendingthelatent-image holdtime

fortheunsensitized andsulfur-sensitizedemulsionsinahumidifiedairenvironmentcould

indicatewhether an equilibrium would_{actually be}obtained.

After 72 hoflatent-image_hold,goldlatensificationand extendeddevelopmentrestored

some,butnot allthe speedlossobservedintheunsensitized emulsion. _Extending

developmenttimecan_developsmallerlatent-imagecenters. After48min ofdevelopment

in_D-19,thespeedlosswas reducedto0. 13 _logE. Thispartial_recoveryofthespeedloss

is probably duetolatent-imagesites smallerthanan_Ag5beingdeveloped.

Gold latensificationreducedthespeedloss from0.18 _logEto0.08_logEafter72 hof

latent-image hold. Thisresultindicatesaportion oftheobserved_fadingis duetolatent

images_becomingtoosmallforconventional_development,butare still recoverablethrough

goldlatensification. Goldcan combine withsubdevelopable silver centers andforma

developablesilver-goldlatent image.i8 Itisnotknownwhat percentage ofthe_remaining

speedlossisduetosilvercentersthatare not gold_{latensifiable,}orto_completelydecayed

latent-imagecenters.

Light latensificationwouldbeabletorecover_Ag2centers_byusinga_{very low intensity,}

longdurationexposure.30

Thisproceduretakesadvantage of_{low-intensityreciprocity}

failure in that_{only pre-existing latent-image}siteswillgrowtodevelopablesize. Facilities

were notavailabletoperformthisexperiment.

VI. Conclusions

1. Atexposuretimes thatcauselittleor no_{low-intensityreciprocity}failure,vacuum

treatmentof an unsensitized or_chemicallysensitized emulsion can resultinspeeds

significandyslowerthan thosefoundinahumidifiedenvironment Thisresultis contrary

toresultsfrom investigators_usinga_longdurationexposure. Theextendedpre

conditioningtechniqueusedinthis thesis_{may have}removedadditional oxygenandwater

vaporfromthephotographic materials. Thisprocedure_{may have}affectedthespeed

differencebetweentreatmentsinvacuum andhumidifiedenvironments.

2. Theunsensitized emulsionhada reductioninthespeeddifference betweentreatmentsin

vacuumandhumidifiedenvironments astheexposuretimewasincreased. Thisreduction

inthespeeddifference may be dueto theonsetof_{low-intensityreciprocity failure in}the

unsensitizedemulsion. Thesulfur-_{and sulfur-plus-gold-sensitized emulsions were not}

sensitiveto thischangeinexposuretime.

3. At0.5_{h between exposing} and_{processing, the}unsensitized emulsionhadthelargest

differenceinspeedbetweentreatmentinvacuumandhumidifiedenvironments. Thisspeed

differenceisattributedtothecreationof aninternal desensitizationsite_bythevacuum

treatment. This internaldesensitizationsite can compete_{effectively for}conduction band

electrons. Thesulfur-sensitized emulsionhad very littlespeeddifference betweenthe two

treatments. This lackofadifferencehasbeenattributedto thedepthoftheelectron_trapat

thesulfur-sensitizationsites.

4. Storageof alatent image inahumidifiedairenvironmentwillinduce a speedlossin

some emulsions. Theunsensitizedemulsionlost significant speedovertimewhereasthe

chemically sensitizedemulsions were_relativelystable. Chemicalsensitization can affectthe

abilityof alatentimagetobeoxidized.

5. Humidifiednitrogenenvironmentsdidnotinducea speedlossovertime. Thisresult

indicatesthatwater alonedoesnot affectthe_stabilityof alatentimageintheunsensitizedor

chemically sensitized emulsions usedinthis thesis.

6. Oxygenappearstobethe_{primary oxidizing}agentfor latent-image decay. Thepresence

of atmosphericwater vaporcan acceleratethis_decayprocess. Boththesize ofthelatent

imageandthesensitization ofthesilverhalidegrain caninfluencethe_stabilityof alatent

imageovertime. Latentimages_{incorporating}gold were stable overthe72hof

latent-image holdtime. The latentimage inanunsensitized emulsiongrainismuchmore_readily

oxidized.

7. Speed lossesintheunsensitized emulsiontreatedin humidifiedair are a result of

latent-imagesites_beingmadeundevelopable. Goldlatensificationrestored_{approximately 50%}of

thelostspeed. Theunrecoverablespeedloss isduetolatent-imagecenters_beingeither

completelyoxidized ortoosmalltorespondto thechemicallatensificationprocedures used.

VII. Future Work

1. Seventy-two hoursoflatent-imageholdwas usedinthiswork. _Extendingthishold

timewoulddemonstratewhethertheobservations reportedherecontinue.

2. Gold latensificationandextendeddevelopmentdidnot restoreallthespeedloss

observedintheunsensitized emulsion after72hoflatent-image hold in a20% RHair

environment. Lightlatensificationwoulddeterminehow much ofthespeedlossnot

chemicallyrecoverableis dueto thecompletelossoflatent image.

3. Asurfacedeveloperwas usedinthis thesis. Theuse ofawhole-grainor aninternal

developershould recover_{any internal}latentimages formed_bypressuredesensitization

Materialsprocessedwithawhole-graindevelopershouldhaveahigherspeedthansamples

processed with a surfacedeveloper.

4. Previousinvestigatorshavereported_conflictingresults_{regarding latent-image}stability.

Partofthisconflicthas beentheintroductionof spectral sensitizers. _Addingspectral

sensitizerstoanemulsionwithaknown latent-image stabilitypattern could_helpresolve

thisconflict.

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