James M. Reilly Director, Image Permanence Institute

What the Guide Is (and What It Is Not) ................... 2The Wheel ................................................................ 4Time Contours for Vinegar Syndrome .................... 7The Time Out of Storage Table ............................... 8Chemical Deterioration of Film Bases .................. 10The Course of the Vinegar Syndrome .................. 13Does the Guide Apply to Nitrate Film? ................. 15Polyester Base Film ............................................... 15The General Philosophy of Film Storage .............. 16History of Film Supports ........................................ 21References ............................................................. 23ANSI and ISO Film Storage Standards ................. 24

l CONTENTS

l The IPI Storage Guide forAcetate Film provides anoverview of environmentalspecifications for film storage.It explains the relationshipbetween temperature, relativehumidity (RH), and vinegarsyndrome, the slow chemicaldecomposition of acetateplastics leading to loss of theirvalue in a film collection.

l The main purpose of theGuide is to help collectionmanagers evaluate the qualityof the storage environmentthey provide for their film. TheGuide is not meant to predictthe life of any individual film; itmerely uses predicted lifespan as a yardstick to measurethe quality of the storageenvironment.

IPI Storage Guidefor Acetate Film

Instructions for Using theWheel, Graphs, and TableBasic Strategy for FilmPreservation

Imag

e Pe

rman

ence

Inst

itute

Roc

hest

er In

stitu

te o

f Tec

hnol

ogy,

70

Lom

b M

emor

ial D

rive,

Roc

hest

er, N

Y 14

623-

5604

Phon

e: 7

16-4

75-5

199

Fax:

716

-475

-723

0

2they apply as well to diacetate, acetate butyrate, andacetate propionate film bases. In short, they are valid (toa first approximation) for all types of acetate film.

The Data in the GuideThe data presented in the Guide were gathered fromaccelerated-aging tests performed as part of an NEH-,NHPRC-, and Kodak-funded research project investi-gating the optimum storage conditions for film.1,2,3 Theend product of the project was a series of predictions forhow long it would take for the onset of the vinegarsyndrome at various storage conditions. (Bear in mindthat the predictions are for when vinegar syndromereaches a threshold level, not for the end of the usefullife of the film.) Each prediction is associated with aparticular temperature and RH combination andassumes that the conditions remain constant. Thepredictions represent the period of time in years thatwould be required for fresh acetate film to start experi-encing noticeable levels of vinegar syndrome; at the endof that period, the film would smell of vinegar butwould still be usable. At that point, however, the filmwould enter a stage in which the pace of deteriorationincreases markedly.

Fig. 1 Components of the IPI Storage Guide forAcetate Film.

l WHAT THE GUIDE IS (AND WHAT IT IS NOT)

The IPI Storage Guide for Acetate Film is a tool forevaluating and planning storage environments foracetate base photographic film, cinema film, andmicrofilms. This is a category that includes agreat many films made between the 1920s andthe present. (Refer to History of Film Sup-ports on p. 21 for more information aboutwhich films in a collection are likely to beacetate and which are not.) Cellulose acetate issubject to a slow form of chemical deteriorationknown as the vinegar syndrome. Nearly everysizeable collection of film has experienced losses dueto vinegar syndrome, and many more losses areexpected in the future. The main symptoms of thisproblem are a vinegar-like odor and buckling, shrink-ing, and embrittlement of the film. All acetate films aresusceptible to such deterioration. Whether it happenswithin a few years or not for centuries depends on thestorage conditions in which the film is kept.

The IPI Storage Guide for Acetate Film dealsprincipally with one aspect of film storage: the generalrelationship between storage RH, storage tempera-ture, and the approximate number of years beforethe vinegar syndrome would become a seriousproblem for fresh, brand-new film. While this ishelpful information, it deals only with cellulose acetateplastic film base deterioration. Other important forms offilm deterioration such as color dye fading, silver imagefading, mold growth, physical damage, etc., have theirown causes and their own relationship to the storageenvironment. There is more to the story of preservingfilm than preventing the vinegar syndrome, and there ismore to the vinegar syndrome problem than justtemperature and humidity conditions, although theycertainly are key factors in the rate of deterioration. Thesection, General Philosophy of Film Storage, begin-ning on p. 16, provides an overview of environmentalconsiderations in film storage and puts the informationspecifically pertaining to vinegar syndrome into abroader context.

The Guide consists of four parts, as shown inFig.1: this booklet, the two-sided Wheel, Time Con-tours for Vinegar Syndrome (one for Fahrenheit, one forCelsius), and the Time Out of Storage Table. Eachcomponent presents information about film storage in adifferent format, providing slightly different approachesto the available data. The data in the Guide wereobtained from experiments on triacetate base film, but

3Although the use of diagnostic tools such as A-D Strips(see p. 14) may provide an idea of how far down thepath of deterioration a particular film has alreadytravelled, it is still nearly impossible to predict exactlywhen a film will become unusable.

Importance of Acid Trapping by EnclosuresThere is another important fact to know about vinegarsyndrome besides its temperature and RH dependence:the acid trapping factor. The process of deteriorationgenerates acetic acid (vinegar) inside the plastic filmbase. Under some circumstances, acidity either canleave the film by evaporating into the air or can becomeabsorbed into storage enclosures. In other situations itcan be trappedprevented from escaping by the storagecontainer. If trapped, it greatly accelerates the rate ofdeterioration. The predictions in the Guide wereobtained from experiments in which the film was keptin tightly sealed foil bags, and so they represent aworst-case scenario where all the acid is trapped inthe film.

Real-life storage may involve more opportunity forthe acid to escape; if that is the case, it will take longerthan predicted for vinegar syndrome to occur. However,most real-life film storage is more likely to be closedthan open. Motion picture film is typically stored inclosed cans, and sheet films are often kept in closequarters in a box or drawer. Though the acid-trappingfactor can certainly make a big difference in how longfilm will last, if you evaluate film storage with theGuide (which assumes maximum acid trapping), you atleast will not overestimate film permanence andprobably will be close to the actual real-life behavior.

Given all these qualifications, what good, then, arethe data? The real value of the data is in enabling us tounderstand in a general way how temperature andhumidity affect the rate of film base degradation. Thedata describe major trends but do not predict the specificbehavior of individual samples of film. In this respect,they are like an actuarial table for a life insurancecompany; the company has no idea when any givenindividual man or woman will die, but it has a very goodidea how long the majority of people will live.

What Do the Predictions Predict?One thing the Guide does not do is to predict the lifespan of individual pieces of film or specific collectionsof film. Because the Wheel, the Contours, and the Tableall express life expectancies in years (nicely matched upwith corresponding storage temperatures and RHs),there is a tendency to view the data as predictive of howlong a given piece of film will last. While such aprediction could turn out to be accurate, there are anumber of good reasons why it cannot be relied on inany individual case.

The predictions are based on extrapolations fromaccelerated aging. They should be seen as a convenientway to quantify and express how good or bad a storageenvironment is for preventing the vinegar syndrome, notas literal predictions of how long a collection will last.

(The Guide is not afortune-tellerit onlytells the relative benefitsof one storage conditionover another.) In orderfor the numbers to betaken as literal predic-tions of when vinegarsyndrome would begin,the collection wouldhave to reproduceexactly the circum-

stances under which the aging experiments were done;all film would have to be fresh, and it would have to bekept in a tightly sealed package at steady, unvaryingconditions. In laboratory studies, such variables must beheld constant throughout the duration of the experimentor the data would not clearly demonstrate the effect ofthose environmental factors.

Each individual film in a collection has a uniquehistory and is in a state of preservation determined byhow it has been stored throughout its whole existenceup to the present time. If we are lucky, we may knowthe storage history of a film collection with someprecision and then be able to more accurately estimateits state of preservation and its prospects for the future;usually, however, we have only a vague general idea.

4l THE WHEEL

Evaluating a Storage ConditionSuppose, for example, that a collection of fresh acetatefilm is kept in an air-conditioned room where itscomfortable for people: 70F (21C), with an RH of50%. (Well assume these conditions are maintainedyear roundnot always an easy thing to do.) Thequestion is, how good are these conditions for the film?To find the answer, consult Side One of the Wheel (theblue side). Rotate the smaller disk until the arrow pointsto the temperature in questionin this case, 70F. Acolumn of numbers will appear in the window. Next,select the RH of interestin this case, 50%. Readingacross on the same line, we find in the window thepredicted number of years for that set of storageconditionsin this case, 40. (See Fig. 3)

At each temperature on Side One, the predictednumber of years until vinegar syndrome begins to be aproblem are shown for seven different humidity values.Notice that lower RHs (dryer conditions) have longerpredicted times, while higher RHs (more humidconditions) have shorter predicted times. This is alwaystrue, regardless of temperature, because the roomhumidity controls how much water will be absorbed bythe film. The water content of the film plays an essentialrole in the reactions of deterioration; therefore, thehigher the RH, the faster the degradation.

Note in Fig. 3 the difference between the predic-tions at 50% RH and 20% RH. Generally, film degradesonly about one third to one half as fast at 20% as it doesat 50% RH. Its not a good idea to go lower than 20%RH, though, because film dries out too much andbecomes brittle. Likewise, its not a good idea to storefilm at RHs above 50%. As Fig. 3 shows, the predictedtime at 70F, 80% RH is considerably shorter than thatat 70F, 50% RH. In addition, high humidity not onlypromotes vinegar syndrome, it also can allow mold togrow (if RH is kept at 70% RH or above for sustainedperiods), leading to irreversible damage to the gelatinemulsion.

The prediction for room temperature (70F/21C)and 50% RH in our example may seem surprisinglyshortonly about 40 years. Nearly every film archivistknows of film that is 40 years old and still in goodcondition. (And many archivists also know of 40-year-old film that is not so good.) To understand the 40-yearprediction, remember that it is the approximate numberof years to the onset of measurable deterioration, andnot the number of years it would take for film to

Approximate Numberof YearsSIDE TWO

SIDE ONE

AverageTemperature

Average RelativeHumidity

The Wheel presents the research results about vinegarsyndrome in a format that makes it easy to evaluate theeffect of a particular storage environment on the lifeexpectancy of acetate film. It makes it possible tocompare the rate of deterioration at a wide range ofconditions, to determine which of several existingstorage environments is better for film, or to considerthe various combinations of temperature and RH thatwould yield a specified life expectancy. The Wheel, asnoted, has two sides (see Fig. 2). Side One is based onthe approximate number of years it would take fresh(new) acetate film to start degrading (to reach 0.5aciditysee p. 14) at various storage conditions. SideTwo is based on the approximate number of years itwould take partially degraded film (film that hasalready reached 0.5 acidity) at various storage condi-tions to reach an acidity level of 1.0. Printed on eachside, around the circumference of the larger disk, is arange of temperatures from 30F/-1C to 120F/49C.Beside the window on Side One of the Wheel is printeda range of humidity levels from 20% to 80% RH in 10%increments. Side Two has only three increments: 20%,50%, and 80% RH. The predicted number of years ateach temperature/humidity combination is displayed inthe window on each side.

Fig. 2The Wheel

5allow the use of the Guide to determine which storageconditions would provide the desired number of yearsbefore the onset of vinegar syndrome. In our examplewe will assume that the institution wants its acetate filmto last a minimum of 100 years.

Is Room Temperature Good Enough?If all the collection materials must coexist in onestorage room, then because of the possible problemswith glass plates at RHs lower than 25%11 (see p. 19),an RH of 40% is decided upon. But what should thetemperature be? The most convenient temperature isprobably a comfortable room temperature of 72F(22C). Using Side One of the Wheel, find the tempera-ture closest to 72in this case, its 70F (shown inFig. 3). Although this is slightly cooler than the 72Fwere interested in, its close enough. At 40% RH, 70F,the predicted years to onset of vinegar syndrome is 50only about half what the institution wants from theirfilm. Clearly, room temperature is not a good choice tomeet the preservation objectives of the institution, andsomewhat cooler temperatures are required.

What Are the Choices?To determine which temperature would yield thedesired 100 years at 40% RH without danger of vinegarsyndrome (remember the predictions on Side One of theWheel are for fresh, undeteriorated film), rotate thesmaller disk of the Wheel until 100 years or moreappears in the window opposite 40% RH. At 60F wefind the desired 100 years (Fig. 4, left). If the collectioncontains older films with a questionable storage history,leading the collection manager to suspect that deteriora-tion is already starting (even though obvious

reach the later stages of deterioration, when it wouldbecome shrunken and brittle. Remember also that thepredictions assume maximum acid trapping and thatreal-life films have usually experienced a changingenvironment, not a steady one. In spite of all thesequalifications, and although the evidence is anecdotaland not rigorous, there does exist enough actual keepingexperience with acetate film to confirm the generaltrends in the Guide. Film kept in warmer than room-temperature conditions does degrade in about 30 years,and film kept at cooler than room-temperature storagefor 50 years shows no signs of degradation. The generaltrends in the IPI data have been confirmed by similarlaboratory studies at Kodak4,5,6 and Manchester Poly-technic in the U.K.7,8,9,10 So, while the predictions shouldnot be taken literally, neither are they unrealistic.However, their importance is that they can be relied onto quantify in a relative manner how much better orworse one storage condition is than another.

Using the Wheel to Plan a New Film StorageEnvironment

The Wheel is also useful for planning a new filmstorage environment. For example, lets assume aninstitution has the opportunity to build a new storagearea for its photographic collectionone that consistsof a variety of materials, including film, glass plates,color and black-and-white prints, etc. Since the collec-tion has sizeable amounts of acetate film in the form ofblack-and-white sheet films and color transparencies,prevention of vinegar syndrome is one of several goalsfor the new storage area.

The first thing to do is to decide how long theinstitution wishes to retain its film collections. This will

Fig. 4 Details of Side One of the Wheel set for60F (left) and 55F (right).

Fig. 3Detail of SideOne of theWheel set for70F/21C.

50% 40 Yrs.

6Fig. 5 Details of Side Two of the Wheel set for60F (left) and 40F (right).

outward signs of it are not apparent), then somewhatcooler temperatures might be chosen to provide a littlecushion on the 100 years. At 55F, 40% RH, forexample, the prediction for onset of vinegar syndromefor fresh film is 150 years (Fig. 4, right).

However, if there is evidence that film in a collec-tion is indeed already deteriorating (odors, waviness onthe edges of the film, etc.), then the situation is differ-ent. Can improved storage stabilize such film so thatit may be kept around for a significant number of years?The answer is a qualified yes, but colder temperaturesare required to achieve a long life.

Planning for Degrading FilmSide Two of the Wheel deals with storage conditions foralready degrading film. The predictions on this side ofthe Wheel are based on the period of years necessary forthe free acidity of film to double from 0.5 to 1.0. Thesenumbers take a little explaining. (For more information,see p. 13 for a discussion of the course of the vinegarsyndrome.) At the 0.5 free acidity level, film may smellof acetic acid, but it is still quite usable. At 1.0 freeacidity the same is true, but the odor may be a littlestronger; not until the free acidity reaches about 5.0 willchanges (buckling, embrittlement) occur to render thefilm unusable.

All this is just to explain that the doubling ofacidity to 1.0 doesnt mean that terrible things suddenlyoccurit only indicates that deterioration has pro-gressed. The acidity has doubled, but there is still someway to go before the film is ruined and useless. Theimportant question is how storage conditions can be

used to slow the progress of deterioration, and one canget a good idea of that from the predictions of timenecessary for free acidity to go from 0.5 to 1.0.

Returning to our example of choosing storageconditions for a mixed collection, if some of the acetatefilm were already degrading, Side Two of the Wheelcould be used to determine how the 60F, 40% RHcondition would affect the progression of deteriorationin such film. Rotate the smaller disk on Side Two topoint to 60F, and locate the nearest RH value to the leftof the window (Fig. 5, left). Side Two has only threeRH values (20%, 50%, and 80% RH), so in this case wewill have to interpolate between the 20% and 50%values. At 60F, 50% RH the free acidity will double inten years, at 20% RH, it will double in 45 years. Since40% RH is closer to the 50% value, it will take about 20to 25 years for free acidity to double in films kept at60F, 40% RH.

This is encouraging, but suppose the institutiondesired 100 years of useful life from already degradingfilm. (Remember that once channeled or embrittled,nothing can be done to reverse the course of deteriora-tionprevention is the only effective method ofpreservation.) Rotating the smaller disk on Side Two to40F shows that, at 50% RH, 50 years is predicted beforefree acidity doubles from 0.5 to 1.0 at that low tempera-ture condition (Fig. 5, right). Interpolating to 40% RH,the prediction is for approximately 100 years. Thus theinstitution can reasonably expect that storage at 40F,40% RH would provide a century of additional usefullife, even for film that was already in the initial stages ofdegradation (at an acidity level of 0.5).

Color FilmOf course, vinegar syndrome is only one considerationin the choice of a storage environment for a photo-graphic collection. In our hypothetical example, colorfilm is also included in the collection. Dye fading alsohas a strong temperature and RH dependence, but nowheel yet exists for color. A decision to choosetemperatures cooler than room temperature will alsobenefit the color film and prints in the collection.12

Many real-life institutions have opted for cold storagefacilities to forestall simultaneously both dye fading andacetate base deterioration.

7The Time Contours for Vinegar Syndrome (representedtwicefor Fahrenheit and Celsius) give a broadoverview of the relationship between temperature, RH,and the time in years for fresh film to begin deteriorat-ing. (See Fig. 6.) Each sloping line on the graph ismarked with a time period (one year, five years, etc.);any point on the line represents a temperature/RHcombination for which the indicated life expectancywould be obtained. About 100 years of life expectancy,for example, could be obtained at 70F, 20% RH, or at48F, 80% RH, or at any of a variety of intermediatecombinations. This graph makes it possible to see thegeneral trends at a glancesuch as how short film lifecan be if stored in hot and humid places, and how longit can be kept under cold, dry conditions (15 centuries at30F, 20% RH).

It is important to realize that these time contoursare useful for a quick approximation of the relationships

between temperature, humidity, and the onset of thevinegar syndrome. Dont try to read between thelines. On this type of graph, interpolation between thelines is difficult because the time intervals are notuniform; to find a life expectancy associated with aparticular set of conditions, use the Wheel or the TimeOut of Storage Table instead.

The Time Contours show the extreme range of lifeexpectancies that are possible with acetate film. Theyrange from very short (only one year at 130F, 50%RH) to very long (more than 1000 years at 30F, 50%RH). Even longer life expectancies are possible at stilllower temperatures, but time periods of more than tencenturies seem a bit unreal to useven though manyobjects survive that are three or four millennia old. Thedownward sloping lines of the Time Contours graphshow how RH affects film life; at higher RHs the lifeexpectancy of film is much shorter.

l TIME CONTOURS FOR VINEGAR SYNDROME

Fig. 6 Time Contours for Vinegar Syndrome

8used at room temperature for a period of time. Theeffects of leaving the storage environment and spendingvarying amounts of time at office conditions (75F, 60%RH) can be profound. Film life expectancy can besignificantly diminished merely by removing film fromspecial storage and keeping it for an average of 30 dayseach year at office conditions.

Using the TableTo use the Time Out of Storage Table, one must firstlocate the row that corresponds to the vault condi-

tions. The Table is based on theassumption that, most of the time,film is stored in a primary storagearea (referred to as the vault,though it could be an ordinary room,a special vault, a refrigerator, or anyother kind of physical storagearrangement). What matters is thetemperature and RH of this primarystorage or vault condition wherefilm normally resides. The three left-hand columns of the Time Out ofStorage Table are marked PrimaryStorage or Vault Conditions. Thefirst two columns are temperature(shown for convenience in bothFahrenheit and Celsius), the third isRH.

Using the Time Out of StorageTable involves finding the rowcorresponding to the primary storagecondition and then looking acrossthe table at columns that refer to howmuch time the film is out of the vaultand kept in an office condition of75F (24C), 60% RH. This is meantto reflect the reality that film is oftenremoved from a vault for use, forexhibition, for curatorial research,because of equipment failure, formaintenance, etc.

Each column heading is markedwith the average number of days peryear that film might spend out of thevault and in the office conditions.Thus the 120 Days column meansthat film spends four months each

Even if a collection has a special environment such as acold storage vault, objects do not always remain there.They may be brought out periodically for use, formaintenance of the vault, or for other reasons. Makinguse of an approach first suggested by Mark McCormick-Goodhart, a research scientist at the SmithsoniansConservation Analytical Laboratory, the Time Out ofStorage Table (Fig. 7) gives data similar to that foundon the Wheel, but with the added dimension of timeout of storage to show how film life expectancy isaffected when film is taken from a storage vault and

l THE TIME OUT OF STORAGE TABLE

Fig. 7 Time Out of Storage Table.

9year in the office condition and eight months in thevault condition. The numbers in the columns are thepredicted number of years for the onset of vinegarsyndrome (defined as reaching 0.5 free acidity) in freshacetate film; the predictions show the combined effectsof being stored part of the time in the vault conditionand part of the time in the office condition.

Consider an example of a vault that is operating at40F, 40% RH (Fig. 8). This is an excellent storagecondition that should provide a very long life for films.If film were always kept in the vault, then the predictedtime before the onset of vinegar syndrome in fresh filmwould be 450 years. The column in the Time Out ofStorage Table marked 0 Days repeats the samepredictions as Side One of the Wheelthis simplymeans the film never leaves the vault. Looking acrossthe row, the predicted number of years drops off sharplyfrom 450 down to 60 as the average number of days peryear out of the vault increases.

At 30 days per year out of the vault, the predictedtime is only 175 years, less than half of the value for 0days. It isnt difficult to imagine circumstances in whichfilm would average 30 days per year out of a coldstorage vault, considering all the possible reasons forintentional or unintentional removal or equipment

shutdown. If the film is out an average of 120 days peryear, the predicted time is only 60 years, about 13% ofthe life expectancy if it never left the vault.

What Happens to Film Out of Storage?The longer the time out of the vault, the more thewarmer condition takes over in determining theoverall life expectancy of the film. Note that in readingdown the column marked 120 Days out of storage(Fig. 7), there is little or no benefit from having a filmvault any colder than 50F. The time spent at theoffice condition is determining the life expectancy ofthe film. No matter how much colder than 50F thevault condition may be, the four months per year at75F, 60% RH dictates that only 60 years will passbefore the predicted onset of vinegar syndrome.

The impact on film life expectancy of the combinedeffects of a storage vault and an office (i.e., use)condition will of course depend on the temperature andRH of both areas. The Time Out of Storage Table ispredicated on an office condition of 75F (24C), 60%RH. The predictions in the Table will be different forother office conditions. IPI can, if desired, calculate acustomized Time Out of Storage Table based on adifferent use environment; institutions can have thisdone on a consulting basis by contacting IPI.

Fig. 8 Detail of the Time Out of Storage Table showing a primary storage condition of 40F.

10

l CHEMICAL DETERIORATION OF FILM BASES

ecules. Detachment of the acetyl groups also can occurin the presence of moisture, heat, and acidsonly, inthis case, free acetic acid is liberated.

The acetic acid is released inside the plastic, but itgradually diffuses to the surface, causing a familiar sharpodorthe odor of vinegar (which in fact is a 5% acetic-acid solution in water). The amount of acetic acid thatcan be generated by degrading film is surprisingly large;expressing it in terms of teaspoonfuls of householdvinegar, in advanced stages of deterioration there can benine teaspoonfuls or more of vinegar for every four feetof 35mm movie film. A typical 1000-ft. can of 35mmfilm can generate enough acetic acid to be equivalent to250 teaspoonfuls of household vinegar!

So, to restate, cellulose nitrate film and celluloseacetate film are somewhat similar in that they are bothmodified forms of cellulose, and both can slowlydecompose under the influence of heat, moisture, andacids. Not surprisingly, the conditions of storage thatare good for nitrate are also good for acetate, and viceversa.1,2 However, the symptoms of deterioration, whenit does occur, are rather different in the two film types.

The Effects of Free Acetic AcidThe oxidizing and highly acidic nature of liberated nitrogroups has been described above, but what are theeffects of free acetic acid? In some ways, they are muchmore benign. Acetic acid is not a strong acid (it wontaggressively rust cans unless present in large amounts).It is not a strong oxidizer, so the silver image is notfaded to orange-red as is often the case in nitratedecomposition. In extreme cases, vinegar syndrome canlead to softening of gelatin, but in general the emulsionsof degrading acetate films remain in much better shapethan nitrate film emulsions do. There is not much colorfilm on nitrate base, but one effect of acetic acidgeneration in acetate film is to accelerate the fading rateof some color dyes in color film.

Chemical Deterioration of NitrateMany archivists are familiar with the slow chemicaldeterioration of cellulose nitrate film,13,14 but they haveassumed that cellulose acetate (so-called safety film)is something entirely different. It turns out that cellulosenitrate and cellulose acetate both share a built-inpropensity to degrade; both these plastic materials aremodified forms of cellulose, and both have a regrettabletendency to become un-modified by the same kinds ofchemical pathways. To make nitrate plastic in the firstplace, nitro (NO

2) groups are grafted onto the long

molecular chains of native cellulose.15

As long as these side groups stay put, all is well.But in the presence of moisture, acids, and heat theytend to become detached, liberating the nitro groups.16

The nitro groups are very harmful substances to letloosethey are strongly acidic and strongly oxidizingin nature. They fade silver images and make gelatin softand sticky; their highly acidic fumes rust film cans andembrittle paper enclosures.17 This, however, is nitratea sad tale, but one already told many times. How doesacetate degradation differ from nitrate degradation, andwhere does the vinegar syndrome come in?

Acetate Film and Vinegar SyndromeVinegar syndrome is a problem that affects onlycellulose acetate plastic materials.18 In acetate film theside groups are not nitro (NO

2) but acetyl (CH

3CO

see Fig. 10). As with nitrate, all is well as long as theseacetyl groups remain grafted onto the cellulose mol-

Fig. 10 A portion of a cellulose acetatechain. Two units shown; molecule goes on.

Fig. 9Ruined gelatinin degraded35mm nitratemotion picturefilm.

ACETYL GROUPS ACETYL GROUPS

11

Fig. 12 Shrunken,embrittled 35mm acetatemicrofilm.

Recognizing Vinegar Syndrome

Vinegar OdorThe vinegar smell is perhaps the most obvious symptomof acetate base deterioration, but it is not the only one;if an unpleasant odor were the only consequence ofdegradation, many ruined films would still be with us.Unfortunately, other chemical and physical changestake place in acetate film as the acetyl side groups aresplit off. The vinegar odor is a warning that chemicaldeterioration is progressing in the acetate film base.

EmbrittlementOne of the physical changes that occurs in the advancedstages of deterioration is the embrittlement of the plasticbase, in which a formerly supple and strong material ischanged into a weak one that easily shatters with theslightest flexing. This is a consequence of the fact thatcellulose acetate is made up of long chains of repeatingunits (i.e., it is a long-chain polymer). When acetic acidis liberated as the acetyl side groups come off, the acidenvironment helps to break the links between units,shortening the polymer chains and causing brittleness.

ShrinkageAnother consequence of acetate-base decomposition isshrinkage. With the polymer chains breaking intosmaller pieces, and with the side groups splitting off(literally making smaller molecules), the plastic filmbase begins to shrink. Film can shrink for other reasonsthan deterioration (some small amount of shrinkageoccurs over time through loss of solvents from thebase), but really destructive shrinkage is a result ofvinegar syndrome. Shrinkage greater than about 1% isenough to cause real trouble for cinema films.

In advanced stages of deterioration, shrinkage can

be as much as 10%a huge amount. The acetate basegets much smaller, but the gelatin emulsion frequentlydoes not (it isnt undergoing deterioration, so it stays thesame size). The result is that something has to give;eventually the bond between the emulsion and base letsgo in some areas, thus relieving the stress caused bybase shrinkage. The emulsion is now buckled up in away that archivists describe as channeling. Cut sheetfilms (4 x 5, 8 x 10, etc.) quite often are severelychanneled in the later stages of acetate degradation (seeFig. 11). Sometimes the emulsion actually tears as itbuckles. Sheet films have gelatin on both sides of thebase; the gelatin on the non-emulsion side is thereprimarily to control curl. When shrinkage occurs, thegelatin will buckle up and channel just as the emulsiondoes.

Because the gelatin emulsion usually stays intactthrough the degradation process, for sheet films it ispossible to save the image by dissolving the emulsionaway from the shrunken base using solvents. Once ithas been freed from its original support, it can be madeflat and photographed, or else transferred to a newsupport. This is a delicate and (because of the solventsused) a potentially hazardous undertaking. It certainly isexpensive to do with a large film collection. Degradedmotion picture films cannot be restored this way, butsheet films often can. Even torn emulsions can be dealtwith successfully. For very important images, the costof this kind of restoration can be justified; unfortu-nately, for most images the cost is too high.

Fig. 11 Shrinkage dueto deterioration inacetate sheet film leadsto severe buckling of theemulsion away from theplastic film base.

Fig. 13 Shrunken,embrittled 16mmacetate motionpicture film.

12

Crystals or Bubbles on the FilmAnother consequence of base deterioration is theappearance of crystalline deposits or liquid-filledbubbles on the emulsion.18 This is evidence of plasticiz-ers, additives to the plastic base, becoming incompatibleand oozing out on the surface. They can appear oneither the base or emulsion side of the film. Plasticizersare chemical additives that are mixed in with thecellulose acetate during manufacture; normally they aredistributed throughout the whole plastic support.5

Plasticizers make up about 12% to 15% by weightof the film. Their purpose is twofold. Their main job isto slow down the rate of burning of the film, should itever catch on fire. The awful tragedies that occurredbecause of the high flammability of nitrate film (firesthat consumed film vaults, sometimes killing manypeople) made the photographic industry very carefulabout the burning properties of safety film.19,20 Thehigh plasticizer content of acetate films reflects a desireto make film as non-flammable as possible. The secondfunction of plasticizers is to reduce the dimensionalinstability of film due to solvent loss or humiditychange. All cellulosic films will shrink under dryconditions and expand under damp conditions; minimiz-ing this behavior is an important role of plasticizeradditives. (Nitrate film also contains plasticizers thatexude onto the surface as deterioration progresses.)

At the time of manufacture, acetate films readilyretain the incorporated plasticizers. However, ifchemical deterioration should occur later on, the

capacity of the base to retain the plasticizer is reduced,and the plasticizer exudes out of the base and crystal-lizes on the surface. Most commonly this takes the formof needle-like crystals which melt away under mild heatand which re-form when the heat is taken away. In somefilms, the plasticizer is exuded as a liquid; bubbles formunder the emulsion, typically in the center of the film.The exudation of plasticizers is associated with moreadvanced stages of degradation.

Pink or Blue Colors on Deteriorated Sheet FilmsStill another consequence of vinegar syndrome is theappearance of pink or blue colors in some sheet films.18

This is caused by dyes incorporated into the gelatinlayer on the back side. Such dyes are called antihalationdyes because they prevent halos in the image.* Thesedyes are supposed to have been made colorless whenthe film was processed, but when acetic acid is formedduring deterioration, the acid environment makes thedyes go back to their original pink or blue color. (Pinkcolors are found in some Kodak films, while blue colorsare found in some Agfa and Ansco films.)

Fig. 16 Bubbles of liquidplasticizer that have formedunder the emulsion ondegraded acetate sheetfilm.

Fig. 14 Degraded acetate sheet film showingchanneling and circular bumps of crystallizedplasticizer under the gelatin emulsion.

Fig. 15 Close-up view ofcircular bumps of solid,crystalline plasticizer astypically found on de-graded acetate sheet film.

* Halos are unwanted circles of light that show up around a brightobject in the imagea street lamp in a night scene, for example. Thisis a disturbing, unreal effect caused by light reflecting off the filmbase during exposure. The gelatin coating on the back side of sheetfilms is a convenient place to put some dyes that would absorb thisunwanted light and keep it from forming halos in the image.

13

l THE COURSE OF THE VINEGAR SYNDROME

It is useful to understand the progression of acetatedeterioration so that the condition of a film collectioncan be assessed more knowledgeably. Of all the changesbrought about by degradation, the first sign is usuallythe vinegar odor. Fig. 17 shows how acidity builds up infilm base over time. It is the shape of this curve that isimportant, because it describes how acidity is at firstalmost non-existent, then for a long time builds upgradually, little by little. Then, after the acid levelincreases to a certain point, the increase suddenlybecomes very rapid. Before this point, acidity risesslowly. After it, large amounts of acid are generated in ashort time.

How Storage Conditions Influence theCourse of Deterioration

The reason why degradation follows this course is easyto understand. Recall that acetic acid is formed whenthe acetyl side groups are split off from the cellulosemolecules (Fig. 10). There are three factors that inducesuch changes: heat, moisture, and acid. In the earlystages (the induction period, before the sharp turnupward) there is little acid present, so the reaction rateis determined primarily by heat and moisture.During this long, slow buildup, the storage environmentplays the decisive role. The temperature of the storageroom determines how much heat energy is available topush deterioration along. Likewise, the amount ofmoisture present in the film is governed by the relativehumidity of the storage area. Thus environmentalfactors can influence whether the induction period islong (perhaps centuries) or short (just a few decades).

Autocatalytic Behavior in Deteriorating FilmThe sharp bend in the time-versus-acidity curverepresents the point when acidity becomes anothermajor factor, along with heat and moisture, in determin-ing the rate of deterioration. Although the environmentstill influences the rate of degradation, the moreadvanced deterioration becomes, the more thereaction rate is influenced by the presence of acidity.The reason is that the reaction is now feeding onitselfdisplaying what scientists call autocatalyticbehavior. A catalyst is a substance that speeds up achemical reaction but is not consumed by it. When areaction is catalyzed by acids as it is in acetate film, andacid is a product of the reaction itself, you have anautocatalytic system. The acetic acid that is liberated asthe acetyl groups split off catalyzes the removal of otherside groups, and the whole process snowballs.

Free AcidityThe Best Way to MeasureDeterioration

The sharp upward turn in the time-versus-acidity curvein Fig. 17 is called the autocatalytic point. Its labeledwith the value 0.5, which takes some explanation. Thenumber 0.5 is a measure of the free acidity in the filmbase; free acidity is not the same as a pH value. Itrepresents the total amount of acid present in the filmbase.* ANSI Standard IT9.1-1992 specifies the methodused to obtain free acidity measurements. The ANSI

Fig. 18 Later stages of acetate deterioration involvebrittleness and channeling of the emulsion, but thesilver image usually remains in good condition.

Fig. 17 Time-versus-acidity curve for acetate film.The autocatalytic part of the curve occurs at about 0.5free acidity, the point chosen as the basis for predic-tions of the onset of vinegar syndrome in the Guide.

HIGH ACIDITY(SEVEREDETERIORATION)

TIME

ONSET OFVINEGARSYNDROMEA

CID

ITY

*The free acidity values actually are derived from the volume ofalkali that is necessary to completely neutralize the acidity of the filmbase.

14

0

1

2

3

Fig. 19 Measuringfree acidity in thelaboratory.

method was the way inwhich free acidity wasmeasured in the film baseduring IPIs research projecton acetate deterioration. Allthe parts of the Guide (theWheel, the Time Contours,and the Time Out of StorageTable) are based on freeacidity measurements. Freeacidity appears to be themost sensitive and reliablemeasure of acetate degrada-tion, and that is why theGuide is based on it.

Some landmarks on the free acidity scale are 0.05(the very low level of free acidity typically found infreshly manufactured films) and 0.5 (which wevealready seen is approximately at the autocatalytic point).Advanced stages of deterioration (which are marked byvery strong odor, shrinkage, buckling, and plasticizerexudation) often have free acidity levels of 5.0 to 10.0and sometimes even higher (see Fig. 17). At the 0.5 freeacidity level, the film will smell of vinegar, but it maynot have any other symptoms of degradation and will beperfectly usable. However, it will degrade ratherquickly from then on unless kept in low-temperature,low-RH storage, as shown on Side Two of the Wheel.

The Goal of Good Film Storage: KeepingFree Acidity at Low Levels

Side One of the Wheel, the Time Contours, and theTime Out of Storage Table are based on predictions,derived from accelerated aging, of the number of years(at constant temperature and RH) before fresh film willreach a free acidity level of 0.5. Knowing the impor-tance of the 0.5 autocatalytic point in the overall courseof degradation helps to put the meaning of the Wheelspredictions in perspective. The goal of good storage isto keep the film from ever getting to the 0.5 auto-catalytic point in the first place, because once there,its useful life from that point on (at least if kept atroom temperature) will be short.

The same kinds of predictive mathematical modelsthat were used on the accelerated-aging data to predictthe number of years until fresh film reaches 0.5 freeacidity also can shed some light on how fast things willhappen after the 0.5 acidity point is reached. (Predic-tions for doubling of free acidity from 0.5 to 1.0 aregiven on Side Two of the Wheel.) The best inferencesthat we can make from the accelerated-aging tests

indicate that film in the early stages of deterioration stillcan be preserved for many years by improved storage.Although nothing can bring back severely degraded,channeled film, something can be done for film that isstill in the early stages of deterioration.

Storage Strategies for Degrading FilmOne of the primary strategies for dealing with nitratefilm in collections has been to segregate it from theother film materials. This has been done for tworeasons: because of the potential fire hazard21 andbecause the acidic and oxidizing fumes from degradingnitrate film may infect other, still healthy, films.17 Doesthis make sense to do with degrading acetate? Theavailable evidence on this point is limited. While insome circumstances deterioration appears to havespread from film to film, one cannot be sure of theextent to which absorption of acid vapors helped totrigger the degradation.

Laboratory experiments show that acetic acidvapors are readily absorbed by fresh film, and this willlead to faster deterioration. In practice, however, itsquite difficult to judge when a threat actually exists.Where at all practical, films showing vinegar syndromeshould be segregated. However, this is not alwayspossible, and having a little degraded acetate film in alarge, well-ventilated room may not infect othermaterials. In such cases the measurable acetic acidconcentration in the room may be very low. On theother hand, having some strong-smelling film inside aclosed container with good film will likely cause fasterdeterioration in the good film, because the concentrationinside the box can be rather high. More research isneeded to explore the practical aspects of this phenom-enon, but until then, film archivists will have to usetheir own best judgment about when and how degradingacetate film should be segregated from the rest of acollection.

Use A-D Strips to: Document the extent of vinegar syndrome Determine when film must be duplicated Check new acquisitions for deteriorationSafer, more accurate than sniffing.Use with all types ofmicrofilm, cinema film,and pictorial film onacetate base.

A new tool tosafely check yourfilm collection forvinegar syndrome!

For more information, contact IPIby phone (716-475-5199) or fax(716-475-7230).

15

l DOES THE GUIDE APPLY TO NITRATE FILM?

In the section on chemical deterioration of film bases, wementioned the chemical similarities between cellulosenitrate and cellulose acetate and pointed out that the samefactors (heat, moisture, and acids) govern the rate ofdeterioration in both materials. Do the data in the Guidetherefore apply to nitrate film as well as acetate? In a generalsense, yes. Trends similar to those seen in the effects oftemperature and RH on the rate of acetate deterioration areseen for nitrate deterioration as well. At this time, IPI haslimited data on the behavior of nitrate films, so a wheel fornitrate does not exist.

IPIs 1988-1990 study of film-base deteriorationincluded a 50-year-old sample of nitrate motion picturefilm; its response to the storage environment (andtherefore its predicted life expectancy) were much thesame as that of acetate film.1,2 This somewhat surprisingresult also occurred with some of the samples in afollow-up study at IPI. But there is an importantdifference between nitrate and acetate that also showedup in IPIs follow-up study. Nitrate film is like the littlegirl of the old nursery rhyme: When she was good shewas very, very good, but when she was bad she washorrid.

Samples of nitrate seemed to divide into twogroups: those that were in apparent good shape andperformed similarly to fresh acetate, and those that were

in apparent good shape butdegraded very quickly in theaccelerated-aging tests. Some ofthe nitrate film samples* used inthe research had slightly moreacidity initially, and these de-graded faster. An attempt wasmade to seek out nitrate samples in as good a conditionas possible, but differences necessarily will exist amongsuch older materials.

IPIs experiences with nitrate confirm what manyfilm archivists already knew about nitrate film: itsurprises you both with how long it can last and howquickly and utterly it can deteriorate. Nevertheless, thepositive outcome of IPIs research is that some nitratefilm can have a very long lifeas long a life as ac-etateif stored well. The Guide can offer insights onwhat kind of storage environment is best for nitratefilm: the cooler the better, with RH not lower than 20%or higher than 50%. The further nitrate film has alreadyprogressed along the path of deterioration, the moreessential it is to store it at low temperatures. Manycollections have opted for near- or below-freezingtemperatures for their nitrate film materials.

Polyester films, introduced in the mid-50s, now comprise asignificant fraction of archival film collections (p. 22 hasmore information on which films are likely to be onpolyester supports). Polyester film base is inherently morechemically stable than either cellulose nitrate or celluloseacetate.2,4,5 With nearly 50 years of manufacturing andkeeping experience behind it, polyester film support hasshown exceptional chemical stability and overall goodphysical performance. When there is a choice betweenpolyester and acetate film supports, polyester is clearly thebest one for archival use.

Although polyester base is also subject to chemicaldeterioration (nothing lasts forever), accelerated-aging testsshow that it will last five to ten times longer than acetateunder comparable storage conditions.2,4 Such testing showstemperature and humidity dependence in polyester basedeterioration, so good storage is still important to get thelongest life from polyester film. To date, there have been noreported cases of chemical deterioration of polyester base inarchival collections. When such deterioration does occur,

brittleness and loss of tensile properties will likely be amongthe symptoms.

The excellent chemical stability of polyester film baseoffers the opportunity to create photographic records ofunparalleled permanence, even at room temperatureconditions. Gelatin emulsion layers have the potential to lastfor centuries; together, polyester base, gelatin emulsionlayers, and the correct choice of image substance will yield apictorial recording medium that should survive fivecenturies or more at room temperature and moderate RH.Although conventionally processed silver images are notequipped to withstand the slow attack of atmosphericpollutants, they can be chemically treated to becomevirtually unalterable.27 Thus black-and-white films onpolyester base, together with appropriate stabilizingtreatment of the silver image, can provide an extraordinarilylong-lived pictorial record.

l POLYESTER BASE FILM

* Since nitrate film hasnt been manufactured for forty years, all thenitrate samples were at least a half-century old.

16

Vinegar syndrome is only one consideration in deter-mining the best storage conditions for film. The needsof other film componentsthe gelatin emulsion, and thesilver or dye imagemust be taken into account aswell. Beyond the physical and chemical nature of filmas an object, storage conditions also have implicationsfor how a collection can be accessed and used. Goodstorage can be costly, so its vital to be clear about thenecessity of a proper environment from a technicalpoint of view. A brief review of the needs of each filmcomponent will help establish a context in which toplace the issue of vinegar syndrome. The principalfactors in the storage environment that affect film aretemperature, RH, and pollutants. Acting alone, or moretypically, acting in combination, they can have signifi-cant effects on the deterioration of gelatin, silver, anddyes.

TemperatureHeat energy makes chemical reactions happen faster.The higher the temperature, the more vigorously atomsand molecules vibrate and move around, colliding witheach other with greater force, thus becoming morelikely to react. The common forms of film deteriora-tionvinegar syndrome and color dye fadingarechemical reactions occurring in the plastic or dyemolecules. Temperature plays a key role in determiningthe rate of chemical reactions, and that is the basis forthe simple truth that cooler conditions (all other thingsbeing equal) are always better for film than warmerones.

How Big a Difference Does Temperature Make?In other words, how much improvement in deteriorationrate can be obtained by low temperature storage? Candeterioration reactions be completely stopped? Only atabsolute zero (definitely not a recommended storagecondition!) are all chemical reactions stopped. Other-wise, the reactions will have some finite rate, howeverslow. The good news is that very dramatic improve-ments in deterioration rate are possible, especially whencompared to room temperature.

The Wheel and Table in the Guide show that thereactions of vinegar syndrome will take about 17 timeslonger at 30F than at 70F. There is no single idealstorage temperature for film, no one temperature wherefilm is happiest. The deterioration reactions that occurin its gelatin emulsion, plastic base, or color dye imageare always moving forward, sometimes faster, some-

times slower, according to the amount of heat energyavailable. It is up to us to decide whether the storagetemperature we are providing for film is low enough toensure the life expectancy we require. The purpose ofthe Guide is to provide the link between environmentalconditions and the rate of the vinegar syndrome, sothatat least as far as this one form of deterioration isconcernedwe know what conditions we must have tomake film last as long as needed.

Silver ImagesBlack-and-white images do fade (rather a lot), andchemical reactions involving metallic silver are the rootcause. However, temperature plays only a limited rolein silver image fading.

Dye ImagesBecause of the problem of dye fading, we have to worrymuch more about storage temperature with color film.12

Some organic dyes are stable, others are not. Textiledyes usually wont fade in the dark within a fewdecades, but photographic dye images do. Many peopleare familiar with the purple cast in some old colormovies or prints. This is due to the fact that the image isreally made up of three different dyescyan, magenta,and yellowand the magenta (reddish-purple) dyetypically lasts the longest. After the other two fadeaway, all thats left is the magenta dye.

The dyes in color film are complex organic mol-ecules that lose their color if structural rearrangementsoccur. The heat energy present at room temperature isenough to cause significant fading, so cold storage isrecommended for color photographic films. ANSIStandard IT9.11-1991 cites a maximum temperature of2C (35F) for extended term storage of color film.Older color products (pre-1980) had less inherent dyestability than contemporary films, so collections ofolder color material are hit with a double whammy;the color has only about 20 to 30 years at room tempera-ture before fading becomes significant, and the film isalready approaching that age. Low temperature storagemust become a top priority for institutions serious aboutkeeping color film in good condition.

The good news about color film is that cold storagecan slow dye fading to such an extent that centuries oflife are possible. The act of thawing and re-freezing filmdoes not harm it.22 Ice crystals do not form in the film asit is frozen, and concerns over damage from taking filmin and out of cold storage have not been borne out byexperience. Many institutions and organizations have

l THE GENERAL PHILOSOPHY OF FILM STORAGE

17

had success with cold storage, in small and largeinstallations alike. However, cold storage has pitfalls;for example, condensation on the film when bringing itfrom cold storage must be avoided. Frost buildup insidecold storage areas can cause damage in some circum-stances. Practical aspects of cold storage are outside thescope of this publication; it is a complex subject,daunting at times, but quite manageable if properlyplanned.23 Any institution seeking to implement coldstorage should get help from qualified preservation andengineering professionals.

Relative HumidityRelative humidity is a second decisive factor, but onewith complex effects which take a little more explana-tion. What really matters is the amount of availablewater in the film base or in the gelatin. Water is anecessary reactant in vinegar syndrome and imagefading. Removing all the water would seem a simpleand effective way to preserve film, but unfortunately itisnt a desirable thing to do. Without some waterpresent, gelatin and acetate film would contract andbecome so brittle that they might crack when handled.

The amount of water present in the film is deter-mined by the relative humidity of the storageenvironment. For example, consider film which hasresided a long time in a room at 50% RH and is thenbrought to another room where the RH is only 20%. Atthe new, low RH, moisture leaves the film and evapo-rates into the air. At the same time that water is leavingthe film, some few water molecules are also beingabsorbed by the film from the air, so that both evapora-tion and absorption are going on simultaneously. Butbecause the air is at low RH, much more water isevaporating than being absorbed, and the net flow isfrom the film into the air. As the process continues, thefilm begins to dry out; its holding less moisture now, sothe rate of evaporation begins to slow down. Eventuallyan equilibrium is reached when continued waterabsorption from the air is perfectly matched by con-tinual evaporation of water into the air.

Regardless of what the temperature is, its theRH that is going to govern how much water remainsin the film after the equilibrium is attained. At lowRH, there will be very little water absorbed by the film;at high RH the equilibrium point will shift, and themoisture content of the film will be much higher.

Gelatin Problems and RH

MoldNearly all film has an emulsion layer of gelatin. Gelatinhas proven to be a durable substance except underprolonged damp conditions, when it is prone to attackby mold. Gelatin is an ideal nutrient for mold growth.Although some antifungal additives are used in photo-graphic films, the photographic industry so far has notdeveloped a way to prevent mold. Any time the ambientRH remains above 70% RH or so for several days, moldgrowth is possible. Good air circulation greatly reducesthe chances of mold damage. There are no satisfactoryremedial treatments for mold damage to gelatin (moldreleases enzymes which soften and dissolve gelatin andalso cause stains). Prevention is the only practicalanswer. Mold spores are almost omnipresent; wheneverthere is enough moisture, they will propagate and grow.

Chemical AttackGelatin is also subject to slow chemical attack by acids,alkalies, and oxidizing air pollutants, leading to loss ofstrength and ultimately to softening and inability towithstand immersion in water. Such chemical attack isinfluenced by the moisture content of gelatin (i.e., byambient RH), but it generally takes so much longer tohappen than other forms of deterioration (such asacetate base degradation or fading of color dyes) that itis not even noticed. However, in the case of polyesterfilm (the base of which is very stable at room tempera-ture),4,24,25 the base may last long enough that the slowchemical deterioration of gelatin becomes the limitingfactor in the survival of film. This presumes, of course,that the image component survives that long as well. Inthe case of nitrate film, gelatin can be attacked by thestrong acids and oxidants released by degrading nitratefilm base.

Physical DamageIn addition to mold and slow chemical degradation,gelatin may experience physical damage under exces-sively dry conditions (RH less than 15%). At such dryconditions, the gelatin emulsion may be too brittle for thefilm to be safely handled. Another result of low humidityis the increase in film curl. This causes motion picturefilm to show spoking (a deformation of a roll of filmthat resembles spokes on a wagon wheel).

In summary, the gelatin component of film is beststored at an average RH between 20% and 50%, a rangein which there is enough moisture to avoid brittlenessyet not enough to accelerate chemical deterioration or togrow mold.

18

RH and Silver ImagesThe image component of film can be either metallicsilver (in the case of black-and-white film) or organicdyes (in the case of color film). The response of silverand dyes to the storage environment is radicallydifferent. Lets consider silver images first. RH is acritically important environmental factor in silver imagefading because it facilitates the oxidation (corrosion) ofmetallic silver. The effect of humidity is particularlyimportant in the presence of pollutants (see below).Without moisture present, silver images would notoxidize and, hence, would not fade.

Dye ImagesThe rate of most dye fading reactions is governed inpart by the moisture available in the emulsion layerwhich, of course, is determined in turn by the ambientrelative humidity. Water actually is a reactant in sometypes of dye fading, and so there is also a stronghumidity dependency to dye fading.26 In like mannerwith silver images, the effect of RH is specially impor-tant when pollutants are present. Although dye stabilityis optimum at near total dryness, some moisture (asnoted above) must be present for flexibility of thegelatin.

PollutantsPollutants originating from either the overall environ-ment or from storage enclosure materials have a verystrong effect on silver and dye images, although theyare not usually a significant factor in chemical deterio-ration of film bases.

Silver ImagesContaminants in the air (peroxides, ozone, sulfides,etc.), and contaminants arising from poor-qualitystorage enclosure materials are the substances thatactually react with black-and-white images to causefading.27 How much damage they can do is determinedmainly by the RH of the storage environment. Withoutthe presence of water, even the most aggressive pollut-ants dont have much effect on silver. The higher theRH, the more water is absorbed by the gelatin emulsion(where the silver is), and the greater the chances thatcontaminantsif they are aroundcan react with thesilver.

Another aspect of the importance of RH in silverimage fading is the fact that gelatin shrinks at low RHand swells at high RH. When swollen (as it is at RHsabove 60%), the gelatin offers no resistance to thediffusion of contaminants through the emulsion.However, at RHs below about 50%, gelatin becomes an

increasingly effective barrier to the diffusion of gases,thus protecting the image against the attack of contami-nants.28 So, while we always seek to keep theatmosphere of the storage area clear of pollutants andalways try to use inert, non-reactive storage envelopesand boxes, we rely on an RH of 20% to 50% to be ourprimary line of defense against contaminants.

Dye ImagesColor dyes are quite susceptible to attack by oxidizingair pollutants such as ozone and nitrogen dioxide.29

Recent studies at IPI have shown that the severity ofthis attack is also RH-dependent, partly because of thebarrier properties of gelatin. Sulfur dioxide and hydro-gen sulfide have much less effect on color images thanoxidizing pollutants.

The Best RH Range for Film StorageIn deciding what is the best RH for film storage, wemust take the following into account:

1. The needs of the plastic base.

2. The needs of the gelatin emulsion.

3. The needs of the silver image or of the three dyeimages (cyan, yellow, and magenta).

In the discussion of all the humidity-dependentforms of deterioration (dye fading, vinegar syndrome,silver image fading, slow chemical deterioration ofgelatin) we have suggested an RH range of 20% to 50%as desirable and acceptable. However, whether storageis at the low end of this RH range (20% to 30%) or atthe relatively higher end of this RH range (40% to 50%)can make a significant difference in the long term,especially with vinegar syndrome and dye fading. Thedata in the Guide show about a three-fold improvementin life expectancy (years to onset of vinegar syndrome)at 20% RH over 50% RH. Generally similar improve-ments exist with dye fading in most color films. Thisdifference is definitely not trivial, and this is why theANSI standard for film storage currently specifies 20%to 30% RH where maximum film life is required.

Establishing the Optimum RH within the 20% to 50%Range

It is possible to trade off temperature and RH toachieve a desired deterioration rate; for any giventemperature, the slowest deterioration will be at 20% RH,but the equivalent life expectancy could be achieved atany RH up to 50% by lowering the temperature. TheGuide shows which conditions are equivalent forcontrolling the rate of vinegar syndrome in acetate film.

The issue of storage RH has several practical

19

dimensions, however, which may influence where in theacceptable 20% to 50% RH range a given storage areais operated. Because of geographic location or the typeof HVAC (heating, ventilating, and air conditioning)equipment in place, it may not be possible to operate astorage area at 20% to 30% RH. Another concern ismixed collections, in which film has to share a storagespace with other kinds of materials. Some glass plateswith gelatin emulsions may suffer delamination fromthe glass support at RHs below 25%.11 Other non-photographic materials may be present which cannotsafely tolerate 20% RH. In this event, the best choicewill be to provide a higher average RH, not exceeding50%, and as cool a temperature as is consistent with theneeds of all the objects in the room.

Cycling of Temperature and RHThe use of the adjective average with RH is notaccidental. What counts most in a film storage environ-ment is not the instantaneous humidity value but thelong-term average RH (long-term being on a scale ofweeks or months), because this will determine themoisture content of the film. Even when theyre incontrol, all HVAC systems oscillate somewhat intemperature and RHits in the nature of controls toalways cycle up and down to some extent. Normally wedont notice these oscillations because they are toosmall. The question is, how large can the magnitude ofsuch cycling get before it causes problems with thefilm?

The key point to bear in mind is that temperatureequilibration (film coming up or down to a new airtemperature) is rather fastusually a matter of a fewhours. Humidity equilibration, on the other hand, isusually rather slowa matter of days, weeks, ormonths.12 Changes in temperature per se (i.e., simpletemperature changes that do not result in drying out ofthe film) do not cause any physical damage to film.

Slowness of Humidity EquilibrationHumidity equilibration is slower because moisture mustdiffuse through the walls of boxes, through gaps in thelids of boxes or cabinets, and through any other enclo-sures in which the film might be stored before it can beabsorbed by the film itself.30 If a single strip of filmwere freely hanging in the room on a clothesline, RHequilibration would be substantially complete withineight hours. Film wrapped on a roll and stored in a canor box, might require three months to equilibrate atroom temperature. In cold storage, diffusion is slower,so equilibration takes even longer.

Considering the slowness of humidity equilibrationin most real-life storage circumstances, it is easy to seewhy cycling of RH up or down 10% in the period of anhour or a day hardly matters. The film inside itspackaging has not experienced the change in RHbecause it has been buffered by the storage enclosuresand cabinets.30 Fast cycling between extremes of RH (adifference greater than 30% or so) and particularly fastdrying out of a film should be avoided. But in mostpractical circumstances, the storage enclosures of filmslow down the rate of humidity equilibration enoughthat cycling is not a concern.

Summary of Temperature and RHfor Film Storage

The summary of how environmental conditions canbe used to control chemical deterioration in filmmight be stated as follows:

Make the temperature as low as you can, andpreferably make the average RH 20% to 30%.RHs up to 50% will do no special harm; they willonly result in a faster rate of vinegar syndromeand dye fading than would occur at 20% RH.

Volatiles in the Film Vault AtmosphereAn important aspect of creating a storage environmentfor film is recognizing and managing volatile substancesthat may originate from the film itself. These arise fromthree main sources:

1. Residual casting solvents and other materialsintroduced during manufacture.

2. Residual cleaning solvents used on processed film.

3. Volatile degradation products such as acetic acid(from decomposing acetate film) and nitrogenoxides (from decomposing nitrate film).

The table on p. 20 gives a partial list of volatilesthat might be encountered in film vaults, together withtheir possible sources.

Although only a few studies of film vault atmo-spheres have been done,31 the limited available datasuggest that the substances found in highest concentra-tion are usually cyclohexane, methylene chloride, andn-butanol. The cleaning solvent 1,1,1-trichloroethane isalso commonly encountered. Slow evaporation ofsolvents is a normal behavior of acetate and nitrate filmcollections, and typically the observed concentration

20

of volatiles is extremely low, posing no healthrisks. As long as the acetate or nitrate film base is notdeteriorated, there will be no acetic acid or nitrogenoxides in the film vault atmosphere.

When film collections are stored in areas designedfor human occupancy, the ventilation rates usually aresufficient to keep volatiles at very low levels. If,however, film is stored in large quantities in speciallybuilt vaults, then air purification systems and/orsufficient fresh air exchange are necessary to ensure thatvolatiles do not build up too high. Some large cinemafilm vaults have experienced unpleasant odors, eventhough the film was in good condition and not degrad-ing. Investigation showed that no health risks wereinvolved, but the odors were sufficiently strong to makeworking inside the vaults quite unpleasant. Such caseshave occurred in vaults purposely designed without anyfresh air exchange in order to minimize operating costs.

Apart from the natural slow release of volatilesolvents, when base deterioration begins to occur,additional volatile substances are introduced into thefilm vault atmosphere. Acetate film collections mayrelease acetic, butyric, or propionic acids upon degrada-tion. Since deterioration is acid-catalyzed, exposure toacid vapors is likely to accelerate deterioration inotherwise healthy films. Degrading nitrate films mayintroduce nitrogen oxides and/or nitric acid.17 Strongoxidants from nitrate may cause fading of silver imagesand embrittlement of paper enclosures.

Health Risks from Degrading FilmThe threat from substances originating from deterio-rated film is not limited to collections, however. Humanhealth risks are also present under some circumstances.Good ventilation is essential when handling or inspect-ing degraded films. Latex, polyethylene, or nitrilegloves should be worn when handling degraded film.Throat and skin irritations have been reported due tohandling of deteriorated acetate and nitrate films.32

Working for long periods in confined, poorly ventilatedspaces with large amounts of degraded film definitelyshould be avoided.

Storage Enclosures for Film CollectionsAll films need some form of storage enclosure; in fact,most films have several levels of protective packaging.Enclosures are needed for physical protection againstdust and handling damage, and they also serve to shieldfilm from atmospheric contaminants and fast changes inenvironmental conditions. All enclosures should bechemically inert toward the components of filmthebase, the gelatin emulsion, and the silver or dye image.Much damage has been done by reactive, poor-qualitypapers, adhesives, and cardboards. Any enclosure that ismade from such materials must meet the generalrequirements outlined in ANSI Standard IT9.2-1991 andmust pass the ANSI Photographic Activity Test (ANSIStandard IT9.16-1993). The PAT guarantees that theenclosure will not chemically interact with the film tocause staining or fading.

Table of Volatile Substances Possibly Found in Film Storage Areas

21

This brief summary of the types of plastic bases used inphotographic, cinema, and microfilm products isdesigned to help collection managers know which filmsare likely to be on nitrate, acetate, or polyester base.This is only a general outline of historical trends; a fulltreatise on the history of film bases and methods toidentify the various plastics is outside the scope of thispublication.

Identifying Film BasesAlthough several physical and chemical tests exist toidentify film bases, most of the time the nature of thefilm supports in a collection can be determined by theage and historical context of the collection (i.e., fromthe historical generalities given below). On occasion,characteristic forms of base deterioration help make itclear which films in a collection are nitrate and whichare acetate. (The nitrate will have sticky emulsions andlots of silver image deterioration, while the acetate willhave channeling and smell of vinegar.)

The easiest method to distinguish polyester filmfrom acetate or nitrate is by the use of crossedpolarizers. Polarizing plastic sheeting (something likethe lenses in polarized sunglasses) can be obtained froma scientific or photographic supply house. Whenpolyester film is placed between two sheets of polariz-ing plastic and viewed by transmitted light, colorfringes appear that resemble the colors formed by oilslicks on ponds. This phenomenon, known as birefrin-gence, occurs only in polyester film. Acetate or nitratefilm will not form bands of color in crossed polarizers.This non-destructive method is very useful in positivelyidentifying polyester film.

Another optical property of polyester makes it easyto tell which roll films in a collection are made onpolyester base. (This is quite handy in microfilmcollections, where acetate and polyester are likely tocoexist.) Film must be wound on a core or on a spokedreel for this method of identification to work. Whenviewed edge on (holding the reel up to a light sourceand looking through the spokes of the reel), polyesterfilm will transmit much more light than acetate ornitrate (see Fig. 20). Some light will pipe through theedges of the film with acetate, but polyester will lookmuch brighter. A little experience with the appearanceof the two types will allow for quick and unambiguousidentification of polyester roll films.

l HISTORY OF FILM SUPPORTS

Fig. 20 When held up to a light source the polyes-ter film pipes light through the edge of the film,while acetate and nitrate do not. (Polyester filmshown at right.)

Historical Overview of Film Formats and FilmBases

Four main types of film formats can be found inarchival collections:

1. Motion Picture FilmPerforated roll films typicallyfound in 35mm, 16mm, and 8mm widths

2. Cut Sheet FilmsSingle-sheet, relatively thickpieces of film commonly found in sizes of 4 x 5, 5x7, and 8 x 10 inches.

3. Amateur Roll FilmsShort rolls or cut singleimages on thin base. Used in hand-held cameras(formats designated by numbers such as 620, 616,828, etc.) by amateurs and professionals. Thiscategory includes perforated 35mm still-cameranegative and slide films.

4. MicrofilmUnperforated roll films in 35mm and16mm widths, and 105mm-width microfiche.

Nitrate BaseMuch nitrate base film is labeled on the edge with theword Nitrate, which certainly makes it easy toidentify. Films on cellulose nitrate support were firstmanufactured in the late 1880s, and nearly all filmsmade between 1889 and the mid-1920s were ni-trate.13,33,34,35 So, any film manufactured before the mid-1920s, in any format, is likely to be nitrate.

Motion Picture Nitrate FilmAll 35mm motion picture film is likely to be nitrate upto 1951, when it was replaced by triacetate. No 16mmor 8mm motion picture film was manufactured onnitrate base.

22

polyester base. Nitrate amateur roll film was notmanufactured by Kodak after 1950.

Microfilm on Acetate BaseMicrofilm is a special application of film that appearedin the 1920s and grew rapidly during the 1930s and1940s. At first, conventional cinema films were used asmicrofilm, but later on, products were manufacturedexpressly for use in document reproduction. Themajority of microfilms produced since the late 1930swere made on acetate base, but during the 1980s, theuse of polyester base increased rapidly.

Polyester BasePolyester plastic film supports are quite different fromacetate in their chemical and physical properties.36 Forexample, polyester cannot be torn (except with tremen-dous effort) unless a nick or cut exists, while acetateand nitrate are fairly easy to tear. Polyester film is notprone to chemical decomposition in the same way thatnitrate film and acetate film are.

Motion Picture Polyester FilmThe first trials of motion picture polyester base filmwere made in the mid-1950s.37 The acceptance ofpolyester base in cinema films has been slowed some-what by difficulty in splicing on traditional splicingequipment. In the 1980s use of polyester base filmbegan to increase, but it is still a small portion of thetotal film used.

Cut Sheet Polyester FilmPolyester base film, introduced in 1955, was first usedin applications such as X-ray and graphic arts filmswhere good physical properties and dimensionalstability were prime requirements. During the 1960s and1970s it gradually replaced acetate as the support formany types of cut sheet films. Some color transparencyfilms are still manufactured on acetate base, but mostother sheet films are on polyester.

Amateur Roll Polyester FilmOnly a small amount of polyester film was manufac-tured for the amateur roll film formats, with the excep-tion of some relatively recent 35mm still camera films.

Microfilm on Polyester BaseToday, nearly all microfilm is on polyester base. Thereasons for switching to polyester support were thegreater chemical stability of the base and the possibilityof using thinner supports, thereby increasing the numberof images on each roll.

Cut Sheet Nitrate FilmAll sheet films were made on nitrate base until the mid-1920s. Sheet films on nitrate base are uncommon after1940.

Amateur Roll Nitrate FilmAmateur roll film camera negatives from 1890 to themid-1940s are nitrate base. These include manypostcard-sized film formats as well as smaller filmwidths. From the mid-1940s to 1950, some were nitrate,some acetate. No amateur roll films were on nitrate baseafter 1950.

Microfilm on Nitrate BaseOnly the earliest microfilms (1920s to mid-1930s) wereon nitrate base. It is quite uncommon to find nitrate basemicrofilms in library collections.

Acetate BaseBoth acetate base film and more modern polyester basefilms are labeled with the words Safety Film. Filmsmarked Safety which were manufactured prior to1955 are definitely acetate, not polyester. Althoughexperiments with acetate film were conducted fromabout 1900 on, large-scale manufacture of celluloseacetate films did not commence until the mid-1920s,when the 16mm home cinema format became popular.Cellulose acetate makes up the largest fraction of filmbases in most photographic collections.

Motion Picture Acetate FilmIn general, cinema and amateur roll films markedSafety are likely to be acetate, regardless of format orage. Thus, collections of cinema film will consistlargely of acetate (apart from 35mm cinema films madebefore 1951, which will be nitrate). At present, acetatecontinues to be the most commonly used base formotion picture films, though since the late 1980s thetrend toward polyester is increasing.

Cut Sheet Acetate FilmSheet films on acetate base were first introduced in the1920s and appeared in quantity in the late 1930s. After1940 nearly all sheet films were on acetate base. Anexception is film pack sheet films (very thin sheets offilm used in special holders where the photographerpulled a paper tab after each exposure to bring a newsheet of film into place); film pack films were last made(by Kodak) on nitrate base in 1949.13

Amateur Roll Acetate FilmIf marked Safety, all the amateur roll films are likelyto be acetate, with a few exceptions of recent origin on

23

l REFERENCES1 P. Z. Adelstein, J. M. Reilly, D. W. Nishimura, and C. J.Erbland, Stability of Cellulose Ester Base Photographic Film:Part ILaboratory Testing Procedures, SMPTE Journal,101:5, 336-346, May-June 1992.2 P. Z. Adelstein, J. M. Reilly, D. W. Nishimura, and C. J.Erbland, Stability of Cellulose Ester Base Photographic Film:Part IIPractical Storage Considerations, SMPTE Journal,101:5, 346-353, May-June 1992.3 J. M. Reilly, P. Z. Adelstein, and D. W. Nishimura, FinalReport to the Office of Preservation, National Endowment forthe Humanities on Grant # PS-20159-88, Preservation ofSafety Film (Image Permanence Institute, Rochester Institute ofTechnology, March 1991).4 P. Z. Adelstein and J. L. McCrea, Stability of ProcessedPolyester Base Photographic Films, Journal of AppliedPhotographic Engineering, 7:160-167, December 1981.5 A. T. Ram and J. L. McCrea, Stability of Processed CelluloseEster Photographic Films, Journal of the Society of MotionPicture and Television Engineers, 97:474-483, June, 1988.6 A. T. Ram, Archival Preservation of Photographic FilmsAPerspective, Polymer Degradation and Stability, 29:3-29,1990.7 N. S. Allen, M. Edge, T. S. Jewitt, and C. V. Horie, Initiationof the Degradation of Cellulose Triacetate Base Motion PictureFilm, Journal of Photographic Science, 38:54-59, 1990.8 N. S. Allen, M. Edge, J. H. Appleyard, T. S. Jewitt, and C. V.Horie, Degradation of Historic Cellulose Triacetate Cinemato-graphic Film: Influence of Various Film Parameters andPrediction of Archival Life, Journal of Photographic Science,36:194-198, 1988.9 M. Edge, N. S. Allen, T. S. Jewitt, J. H. Appleyard, and C. V.Horie, The Deterioration Characteristics of Archival CelluloseTriacetate Base Cinematograph Film, Journal of Photo-graphic Science, 36:199-203, 1988.10 M. Edge. N. S. Allen, T. S. Jewitt, and C. V. Horie, Funda-mental Aspects of the Degradation of Cellulose Triacetate BaseCinematograph Film, Polymer Degradation and Stability,25:345-362, 1989.11 C. McCabe, Preservation of 19th-Century Negatives in theNational Archives, Journal of the American Institute forConservation, 30:41-73, Spring 1991.12 P. Z. Adelstein, C. L. Graham, and L. E. West, Preservationof Motion-Picture Color Films Having Permanent Value,Journal of the Society of Motion Picture and TelevisionEngineers, 7:1011-1018, November 1970.13 J. M. Calhoun, Storage of Nitrate Amateur Still-CameraFilm Negatives, Journal of the Biological PhotographicAssociation, 21:1-13, August 1953.14 C. Young, Nitrate Films in the Public Institution, AASLHTechnical Leaflet 169, (American Association for State andLocal History, 1989).15 W. Haynes, Cellulose, the Chemical That Grows (NewYork, Doubleday & Company, 1953).16 M. Edge, N. S. Allen, M. Hayes, P. N. K. Riley, C. V. Horie,

and J. Luc-Gardette, Mechanisms of Deterioration inCellulose Nitrate Base Archival Cinematograph Film,European Polymer Journal, 26:623-630, 1990.17 J. F. Carroll and J. M. Calhoun, Effect of Nitrogen OxideGases on Processed Acetate Film, Journal of the Society ofMotion Picture and Television Engineers, 64:501-507,September 1955.18 D. G. Horvath, The Acetate Negative Survey (Kentucky,Ekstrom Library, University of Louisville, February 1987).19 C. R. Fordyce, Motion Picture Film Support: 1889-1976, AnHistorical Review, SMPTE Journal, 85:493-495, July 1976.20 C. E. K. Mees, History of Professional Black-and-WhiteMotion-Picture Film, Journal of the Society of Motion Pictureand Television Engineers, 63:125-140, October 1954.21 National Fire Protection Association, NFPA 40Standardfor the Storage and Handling of Cellulose Nitrate MotionPicture Film, 1988 ed., Quincy, Massachusetts, 1988.22 D. F. Kopperl and C. C. Bard, Freeze/Thaw Cycling ofMotion-Picture Films, SMPTE Journal, 94:826-827, August1985.23 W. P. Lull and P. N. Banks, Conservation EnvironmentGuidelines for Libraries and Archives in New York State (NewYork State Library, 1990).24 P. Z. Adelstein and J. L. McCrea, Permanence of ProcessedEstar Polyester Base Photographic Films, PhotographicScience and Engineering, 9:305-313, September/October 1965.25 K. A. H. Brems, The Archival Quality of Film Bases,Journal of the Society of Motion Picture and TelevisionEngineers, 97:991-993, December 1988; Archiving the Audio-Visual Heritage, A Joint Technical Symposium, Berlin, May1987.26 Conservation of Photographs, Kodak Publication F-40(Rochester, Eastman Kodak Company, 1985).27 J. M. Reilly, D. W. Nishimura, K. M. Cupriks, and P. Z.Adelstein, When Clouds Obscure Silver Films Lining,Inform, 2:16-38, September 1988.28 P. Z. Adelstein, J. M. Reilly, D. W. Nishimura, and K. M.Cupriks, Hydrogen Peroxide Test to Evaluate Redox BlemishFormation on Processed Microfilm, Journal of ImagingTechnology, 17:91-98, June/July 1991.29 J. M. Reilly, Preservation Research and Development: AirPollution Effects on Library Microforms, Seventh InterimReport PS-20273-89, Image Permanence Institute, RochesterInstitute of Technology, January 31, 1992.30 V. Daniel and S. Maekawa, The Moisture BufferingCapability of Museum Cases, Materials Research SocietySymposium Proceedings, Vol. 267 (Materials ResearchSociety, 1992), pp. 453-458.31 GC/MS Identifies Odor-Causing Agents, AnalyticalControl, 4:1-2, May-June 1979.32 P. W. Hollinshead, M. D. Van Ert, S. C. Holland, and K.Velo, Deteriorating Negatives: A Health Hazard in CollectionManagement. Unpublished internal report, Arizona StateMuseum, University of Arizona, 1986.

24

(References, cont.)33 R. V. Jenkins, Images and Enterprise, Technol-ogy and the American Photographic Industry 1839to 1925 (Baltimore, The Johns Hopkins UniversityPress, 1975).34 C. E. K. Mees, From Dry Plates to EktachromeFilm (New York, Ziff-Davis, 1961).35 P. Z. Adelstein, From Metal to Polyester:History of Picture-Taking Supports, Pioneers ofPhotography, Eugene Ostroff, ed. (Society forImaging Science and Technology, Springfield,Virginia, 1987), pp. 30-36.36 P. Z. Adelstein, G. G. Gray, and J. M. Burnham,Manufacture and Physical Properties of Photo-graphic Materials, Neblettes Handbook ofPhotography and Reprography (New York, VanNostrand Reinhold, 1977).37 D. A. White, C. J. Gass, E. Meschter, and W. R.Holm, Polyester Photographic Film Base,Journal of the Society of Motion Picture andTelevision Engineers, 64:674, 1955.

ANSI and ISO Film Storage StandardsAmerican National Standard for Imaging MediaProcessed Safety Photographic FilmStorage, ANSIStandard IT9.11-1993 (New York, American NationalStandards Institute).

American National Standard for Imaging MediaPhotographic Processed Films, Plates, and PapersFiling Enclosures and Storage Containers, ANSIStandard IT9.2-1991 (New York, American NationalStandards Institute).

American National Standard for Imaging Media(Film)Silver-Gelatin TypeSpecifications forStability, ANSI Standard IT9.1-1992 (New York,American National Standards Institute).

American National Standard for Imaging MediaPhotographic Activity Test, ANSI Standard IT9.16-1993 (New York, American National StandardsInstitute).

PhotographyProcessed Safety Photographic FilmsStorage Practices, ISO 5466:1992(E), (Switzerland,International Organization for Standardization).

Beginning in 1988, the Image Permanence Institute at Rochester Institute of Technology undertookresearch on deterioration of plastic film supports, with major funding from the Division of Preserva-tion and Access of the National Endowment for the Humanities. Funding was also received from theNational Historical Publications and Records Commission, and from Eastman Kodak Company.Both Eastman Kodak Company and Fuji Photo Film Ltd. provided film samples and technicalexpertise to the project. Those who find this Guide useful will join IPI in thanking the sponsors of thisresearch. Proceeds from the sale of the Guide go toward continuing IPIs scientific research in imagepreservation.

Publication of the Guide was made possible by the assistance of the Andrew W. Mellon Foundation.Additional assistance was provided by the