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s JMMARY OF CURRENT RESEARCH

ON ARCHIVAL MICROFILM

C. S. McCAMY AND C. I. POPE

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
IE NAr lL bureau of standards

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau's activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering. ** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineer

ing Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS

Technical Note 261

ISSUED APRIL 16, 1965

SUMMARY OF CURRENT RESEARCH

ON ARCHIVAL MICROFILM

C. S. McCamy and C. I. Pope

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 Price 25 cents.

Preface

One method of preserving records for archival purpose is

to photograph the records, producing images of reduced size

made up of silver dispersed in a gelatin film, and to keep the

film under conditions suitable for its preservation. This

method has been in use on a commercial scale for more than a third of a century and is widely used in Government and industry. In recent years it has been found that blemishes not

previously noted developed on some such microfilms years after

the films were processed and placed in storage. (1)* Some of

these blemishes were described in detail by Henn and Wiestand

others by McCamy. (1,2) Reference 2 gave recommended procedures for sampling and inspecting film and reporting blemishes.

Large numbers of rolls of microfilm in use in the Government

have been inspected, utilizing these techniques, and the results

of those inspections are being analyzed. The mechanism of

formation of aging blemishes and methods of preventing their

formation are being studied at the National Bureau of Standards

and in laboratories of the photographic industry. The mechanisms

are being elucidated and very promising methods of prevention

have been proposed. Though these matters are still being

studied, those now engaged in microfilming and those planning

records systems for the future have an immediate need for

current information. The purpose of this publication is to

provide guidance based on the findings to date. Although any

prediction of long term stability is subject to change in the

light of new observations, predictions based on these findings

are more than usually tentative because new experimental

results are accumulating daily.

This Technical Note is a summary of a more detailed paper

entitled "Current Research on Preservation of Archival Records

on Silver-Gelatin Type Microfilm in Roll Form* prepared for

publication in the Journal of Research of the National Bureau

of Standards.

Numbers in parentheses refer to numbered references at the

end of the paper.

Ill
Contents

Page

Preface Ill

1. Introduction 1

2. Film Inspections k

3. Experimental Research

3.1 Structure of Blemishes ...

3.2 General Mechanism 10

3.3 Liesegang Ring Phenomenon 11

3.^ Experimental Humidity Control' 11

3«5 Effect of Imbibed Chemicals on Film Exposed to Hydrogen

Peroxide 12

3.6 Experiments With Dry Chemical Contaminants 12

3.7 Biological Studies 12

3.8 Studies of Peroxide Formers 13

3.9 Experiments With Cardboard 15

3.10 Effect of Density 16

3.11 Effect of Gold Protective Treatment 17

k. Recommendations 17

5. References 2k

IV
SUMMARY OF

- CURRENT RESEARCH ON ARCHIVAL MICROFILM

C. S. McCamy and C. I. Pope

, The discovery of aging blemishes on microfilm in storage

has prompted a study of the statistical relationship of incidence to conditions of preparation and storage, the chemical

and physical nature of the blemishes, and measures to betaken

to prevent their formation. This paper is a report of progress in that study with recommendations based on current information. With few exceptions, reports of aging blemishes refer

to negative silver-gelatin type microfilm in roll form.

Extremely small amounts of information loss have been reported.

In some large collections of microfilm, no blemishes have been

found. No evidence of biological attack has been found.

Apparently, image silver is ionized, migrates, and is reduced

to colloidal silver. The reaction often proceeds in the manner

described by Liesegang for other silver-gelatin systems. In

laboratory tests, blemishes formed in the presence of minute

amounts of peroxides, certain imbibed chemicals, and solid con- taminants. Recommendations include: avoiding excessive densities on film, careful avoidance of physical damage to the

image layer, the use of a small concentration of iodide ion in

the fixer, thorough washing, uniform drying, storage at low

temperature and humidity in sealed cans, careful avoidance of

air-borne reactants, increased use of positive copies for

archival storage, and careful periodic inspection of record

films.

1 . Introduction

If a document is intrinsically valuable, an archivist may el§ct to

preserve the original as long as he can. By preserving a photograph of

the document, in a separate place, the preservation of the appearance of

the document is further assured.

There are a number of other reasons that photography is employed for

the preservation of records. Perhaps one of the most obvious is that a

camera can reduce the area occupied by the record. Systems commonly

used today produce images having areas l/lOO to l/lOOO of the areas of

the originals. Photography preserves practically all of the appearance

1
characteristics of the original and does not make transcribing errors.

When placed on a roll of microfilm, a miscellaneous assortment of

documents becomes a uniform continuous film. Once a file has been put

in order in this way, it stays in order. Images on film can be stored

and retrieved by highly automated means. Microfilm can be copied by

automated means for dissemination to users, for duplication to gain

redundancy and thus more assurance of preservation, for dispersion to

insure against local hazards, or to gain the advantages of new

photographic materials.

Perhaps one of the less obvious reasons for microfilming is that the

microphotograph is often more stable than the original document.

Very often a record becomes of archival interest long after the original

is generated. Thus, a high grade of Daper is not always used in

anticiDation of the archival value of the document. In the federal

records there are many letters from private citizens or foreign sources.

The Government cannot control the quality of paper and ink used in the

correspondence it receives.

These factors led to the use of microfilm in commerce, industry,

and Government.

NBS Miscellaneous Publication M-158* published in 1937, gave

(3)

recommended properties of film for permanent records. By Act of

Congress, in 19^0, the National Bureau of Standards was assigned the

responsibility for the maintenance of suitable standards for the

reproduction of permanent Government records by photographic and

microphotographic processes. Subsequent legislation assigned this

responsibility to the Administrator, General Services Administration.

2
The actual maintenance of the standards was continued from 19^+0 until 1957

by the Photographic Research Section of the National Bureau of Standards.

In 19^5 » the American Standards Association adopted a standard

CO

Specification for Photograohic Films for Permanent Records. This

(5)

standard was revised in 1957, the NRS standard was rescinded, and

Federal Standard No. 125A, which simply referenced the ASA standard,

(6) was issued. A modest research program on the stability of photographs

was continued in the Photographic Research Section of NBS.

The chemical mechanisms of fixing, fading, and sulfiding of photographic

images, and chemical analytical techniques for determining residual

(7,8,9)

thiosulfate were studied.

Large numbers of rolls of microfilm processed and preserved at the

National Archives are in good condition after many years and have no

aging blemishes. This demonstrates that, under the right conditions,

microfilm is stable. It is important to know what conditions of film

processing and storage are necessary and sufficient to achieve this

stability consistently. These conditions can be stated with complete

confidence only when the mechanism of formation of aging blemishes is

fully understood. Although a number of questions remain, much has been

learned by inspecting films, correlating the incidence and severity of

blemishes with conditions of processing and storage, and subjecting

films to extreme conditions to induce suspected reactions at an

accelerated rate. This note is a summary of the results of these recent

investigations to date and provides as much guidance as current

information permits.
c. Film Inspections

Large numbers of rolls of federal record film were inspected bypersonnel of the National Bureau of Standards, but it would have been

impossible for the staff of the Bureau to inspect any large fraction of

federally held microfilm in a reasonable time. Employees of other

Government agencies were trained to inspect films and report their findings, using the procedures given in Reference 2. To date over 7 thousand

rolls of film, representing a sampling of about 10 million rolls, have

been inspected and reported. The information is being encoded for a

detailed statistical study, by means of a digital computer, of the interrelationship of all variables considered to be of imoortance. The reports

have shown no obvious indications of conditions greatly different from

those encountered in the initial NBS inspections, upon which the following

observations are based.

Aging blemishes were observed on microfilm in roll form but not on

other films, with the following exceptions. There were two instances

involving nitrate-base film , which has not been used in this country for

many years. One case involved some 9-inch aerial film about 25 years

olf, the other was 35 mm motion picture film about 50 years old. The

aerial film blemishes looked like Type 1* blemishes but those on the

motion picture film were atypical, resembling general fading more than

aging blemishes. A collection of 2 l/2-inch square (No. 120) pictorial

negatives on a fine-grain roll-film manufactured, exposed, processed, and

stored in Europe were found to be very badly affected. No blemishes have

been reported on such pictorial negatives in this country. Blemishes have

Type designations are defined in Reference 2.
been reported on one collection of microfilms mounted on aperture cards.

Since the film had been stored in rolls for some time before it was

mounted, the blemishes may have been on the films at the time they were

mounted. No other cases of attack have been reported on films mounted

on aperture cards. About 35»000 positive microfilm chips mounted on

aperture cards were accumulated in our own office during the period

between 1953 and 1957. This collection has been exposed to ordinary

office conditions, including air conditioning during the summer months.

The collection was recently inspected and no aging blemishes were found.

Films on aperture cards have not been studied further at this time.

Though they are outside the scope of this paper, they are being studied

as part of this research program.

Aging blemishes were not observed on the information areas of

positive copies having dark characters on a light background, although

aging blemishes have been observed on the high-density borders of one

such film and others have been reported.

Microfilm was found stored on reels made of plastic, painted steel,

anodized aluminum, and fiberboard. Some was stored on cores, without

flanges, made of plastic or wood.

The film was stored in cardboard boxes, one reel to a box. Most

boxes were those generally supplied commercially but some agencies, such

as the National Archives, had boxes specially made for their use. The

boxes of film were usually stored in shallow drawers in painted steel

cabinets or on painted steel shelves.

Blemishes were not usually observed on the outer convolution of film

but began, often remarkably abruptly, at the beginning of the second

5
convolution. A frequent exception was the observation of a pattern of

blemishes beneath a rubber band, string, or adhesive tape, used to bind

the roll.

On a given small area on a film, the soots very often displayed a

remarkable uniformity of size. The general features of the outer rings

of ringed spots also tended to disolay similarity over a small spatial

range.

Given the conditions for blemish formation, blemishes appeared to

form more readily at higher densites. ^-Jhen the leaders were fogged,

they were the densest parts of the films and typically had many more

blemishes than other areas on the film.

Blemishes were often concentrated at places corresponding to high

gradients of density. The straight boundary between the dense background

of a filmed document and the clear SDace between frames was sometimes

marked by a nearly solid line of blemishes.

Blemishes were often observed in a nearly continuous string along

scratches in the emulsion.

In a series of frames of copies of aocuments on identical forms,

blemishes were observed on the corresponding characters of as many as 25

consecutive frames.

One of the most significant findings was a collection of about

37,500 rolls of microfilm without blemishes. This film was exposed and

processed at the National Archives and was stored there. The film was

35 mm microfilm manufactured by two different American manufacturers

since 19^0.

Two aspects of the processing at the National Archives are considered

6
notable: the presence of an exceptional amount of iodide ion in the

fixing bath and an exceptionally high consumption of wash water per unit

of filjTi area. The iodide in the fixing bath presumably resulted from

the processing of considerable amounts of positive film along with

negative film. Pope has reported that the presence of the iodide ion

prevents most of the sulfiding of the image during fixing and aids in

(7)

the elimination of residual chemicals during washing. Researchers at

Eastman Kodak Company have found that iodide in fixing baths was

associated with a reduction or complete elimination of aging blemish

formation in a number of private and Government processing plants.

Mr. Robert 0. Bieling of Bell and Howell Company found an increase in

general fading on accelerated aging after such iodide treatment. This

result was confirmed at NBS. Since general fading has not been

associated with iodide in the fixer in actual practice, the accelerated

test may be too severe. On the other hand, the test may be predicting

actual future performance. We have no reports that properly washed film

has faded objectionably, while aging blemishes have actually destroyed

small amounts of information. Since most microfilm images have rather

high contrast, a considerable amount of general fading could be tolerated

without loss of information. On the basis of these considerations, the

addition of 0.2 g of potassium iodide per liter of fixing solution, to

fixing solutions not otherwise containing an equivalent amount of iodide

ion, apoears desirable if the films are stored according to the

recommendations given below.

Mr. Albert H. Leisinger, Jr. of the National Archives arranged to

see what a film once looked like and follow its changes with the passage

7
of time. A certain roll of negative film was manufactured in 1936 and

processed in 1936 or 1937. (Since the film was not exposed or processed

at the National Archives the exact date is unknown.) A copy of the film

was made between 1936 and 19^, one in 1958, and another in 1963. The

original and the copies were photographed using a magnification of about

20. The pre-19^4- copy shows that there were no noticeable blemishes at

that time. The 1958 cony revealed about 3^0 blemishes on one frame of

the negative at that time. The 1963 copy exhibited only those blemishes

already on the negative film 5 years earlier but some growth in the

diameter of spots was observed. The ratio of diameters, as measured on

a number of spots on the prints, ranged from 1.5 to 2. There was no

perceptible information loss. The growth was in the size of spots

rather than in the number of spots.

The blemishes appear lighter than the normal background and

transmit more light at long wavelengths than at short wavelengths.

Because of this spectral transmittance and the ultraviolet and blue

sensitivity of Dhotographic copying materials, the blemishes very often

are not noticed on ohotographic Drints of films having blemishes and the

legibility of the prints appears better than that of the blemished film.

One of the objectives of the initial film inspections was to find

the extent to which Government films were affected by blemishes and to

ascertain whether or not any information had been lost. Of the total

number of collections of microfilms, there was a large fraction that had

some blemishes. Tn the collections having blemishes, a fraction of the

rolls had blemishes. On a roll, blemishes sometimes were and sometimes

were not on the information frames. When blemishes occurred on

8
information frames, only a fraction of the frames were affected. On a

blemished frame, only a fraction of the blemishes were on or around

information characters. Of the six types of blemishes, only the

infrequently occurring Type 2 formed in the characters, although Type 1

sometimes crossed over lines of characters. Other types showed a

natural aversion to attacking the characters. As a result of the

redundancy of the records, the statistical distribution of blemishes,

and the characteristics of the mode of formation of blemishes in the

vicinity of characters, the amount of loss of information in federal

records apoeared to be extremely small. Nonetheless, one agency reported

some such loss in the only existing copies of certain reports having

tabulated numerical data. The only observed cases of actual loss of

information resulted from Type 2 blemishes.

P. R. Achenbach and C. W. Phillips of the NBS Building Research

Division, who are experienced in heating and air conditioning engineering,

examined a few Government microfilm storage facilities. They found that

the buildings were not always well designed for the purpose, air

conditioning was not always adequate, and the practice of monitoring

temperature and humisity at some central location in a room did not

always assure proper control of these variables at the perimeter of the

room where some of the films were stored.

3. Experimental Research

3.1 Structure of Blemishes

The structure and chemical nature of blemishes have been described

(1)

by Henn and Wiest and various tyoes were described and illustrated in

(2)

color by McCamy. The normal photographic grain pattern is absent in
the light colored areas of the blemishes. Cross sectioning of spots

reveals the fact that the whole thickness of the image layer is

generally involved. Spots have been treated in a variety of chemicals

to study the chemistry of various parts of the spots. The structure of

spots has been studied by means of the electron probe microanalytic

technique. All indications are that the yellow to red color is mainly

attributable to the presence of colloidal silver in the interior of the

spots. The dark concentric rings, dark rims, and mirror-like formations

are made up of silver with some silver sulfide.

3.2 General Mechanism

The currently favored hypothesis is that blemish formation is a

chemical reaction in which the normal silver grains are corroded away,

the silver ions migrate, and are in large part redeoosited as colloidal

silver or as mirror-like deposits of silver and silver sulfide at the

upper or lower surface of the gelatin layer. Considerable evidence

(1)

obtained here and elsewhere supports this hyoothesis. An oxidation

reaction of some kind is required to ionize the metallic silver and a

reduction reaction is required to redeoosit the silver. Peroxides can

bring about oxidation-reduction reactions with silver so it is natural

to suspect that blemishes are formed by oeroxides attacking the image

(1)

silver. Why the attack should be localized and why the blemishes

should assume their typical forms are not entirely clear, "he heavy

concentration of blemishes along scratches in the gelatin may be

attributed to the removal of the protective gelatin layer. Any weakness

in the gelatin layer, in the form of a local abnormality of the

permeability to chemicals, or a concentration of reactive or catalytic

10
species could determine the site of attack. Tn the normal image, the

nature of the gelatin deoends on the local density of image silver. The

local concentrations of various chemicals, such as thiosulfates, retained

in the image also depend on the local image density. For these reasons,

the strong influence of the image upon the location and form of blemishes

is consistent with the working hypothesis.

3.3 Liesegang Ring Phenomenon

The very regular concentric ring patterns in the Type 1 blemishes

and less regular concentric ring patterns in Type k blemishes are

strongly reminiscent of the phenomenon first described by

(10)

Ro E. Liesegang and known as Liesegang ring formation. To determine

whether or not Liesegang rings could form on the small scale of interest

in this investigation, the classic experiment of Liesegang was repeated

using a microscopic droplet of silver nitrate solution on a gel layer

containing potassium dichromate. The reaction proceeded as Liesegang

reported, but in this case forming a concentric ring pattern in the size

range of Type 1 aging blemishes, proving that the phenomenon is

demonstrable on this scale. The literature abounds in references to

rings formed in reactions with silver salts in gelatin. Thus, the ring

structure in aging blemishes is not fully explained but neither is it

unprecedented in silver-gelatin systems. It is likely that the mechanism

is the same as that producing Liesegang rings in general.

3.^ Experimental Humidity Control

To obtain various conditions of temperature and humidity for

experimental purposes, various saturated salt solutions were placed in

11
closed containers and the containers were placed in ovens thermostatically

controlled at various temperatures. Numerous studies of such procedures

are reported in the literature, e.g., Reference 11.

3.5 Effect of Imbibed Chemicals on Film

Exposed to Hydrogen Peroxide

Processed and dried microfilm samples were treated 3 min in 0.1

percent solutions of compounds which might be in orocessing solutions or

wash water. The concentration of the comDounds was about B ng/cm of

film. The excess solution was shaken from the samDles, which were then

placed in a l6-oz jar and stored at 60 C and a relative humidity of U3

percent in the presence of hydrogen peroxide. Spots the size of natural

aging blemishes formed in 17 to 72 hours on films containing aluminum

potassium sulfate, boric acid, calcium carbonate, magnesium sulfate,

mono-methyl-para-aminophenol sulfate, potassium bromide, sodium chloride,

sodium nitrate, sodium silicate, and sodium sulfite. Samoles without

imbibed chemicals formed no blemishes under the same conditions of storage.

3.6 Experiments With Dry Chemical Contaminants

The emulsion sides of dry microfilm samples were pressed against

powdered salts and tapped gently to remove loose TX>wder. The films were

stored in l6-oz jars at 60 C and k^ oercent relative humidity. Irregular

but generally round soots formed on film contaminated with ferric sulfate,

potassium iodide, sodium thiosulfate, or sulfur. SamDles without chemical

contamination formed no blemishes under the same conditions of storage.

3.7 Biological Studies

Dr. E. H. Zeitler, of the Armed Forces Institute of Pathology, found

no evidence on blemishes of attack by micro-organisms, confirming the

12
(1)

report of Henn and Wiest.

In our laboratories, dried spores were obtained from cultures of

fungi grown in a gelatin solution. Samples of processed microfilm were

contaminated by brushing dry spores onto the surface of the film and by

treating films with water containing spores. Tests were run at k6

o percent and 75 percent rh at room temperature, and 50 C, in desiccators.

Some fungal growth was observed at 75 percent rh at room temperature but

no spots were formed by the spores. Although spore incubation might

weaken the gelatin and invite attack by peroxides, this effect has not

been observed. Bacterial action by a few organisms on the gelatin

surface, perhaps during drying, later permitting peroxide attack, seemed

a possible biological mechanism. Evidence of such activity has not been

observed, though it should be detectable if present.

3.8 Studies of Peroxide Formers

In the presence of a certain kind of grease, spots developed in two

to four weeks at k6 percent rh and 50 C. This grease had a very faint

odor of rancid vegetable oil, but the mass spectrograph detected nothing

more than water. Infrared spectra of the grease itself and the iodine

number identify it as castor oil hydrogenated about 30 percent. The

double bond compounds of the kinds found in castor oil form peroxides

with the oxygen in the air and polymerization bonding of a molecule with

another double bond molecule releases hydrogen peroxide which can bring

about the oxidation-reduction reaction with the image silver.

The interior of some desiccators was coated about l/8 inch thick

with this grease, from the top to the porcelain plate near the bottom.

13
Microfilm samples were stored at various temperatures and humidities.

Numerous spots formed. The areas of the samples closest to the grease

surface were affected first. The spots formed in the presence of this

grease were visually indistinguishable from naturally occurring spots.

The unsaturated compounds in linseed oil and castor oil and oleic

and linoleic acids were tested for their ability to form spots on film.

Linseed oil and linoleic acid caused numerous spots in 25 days at 50

o percent rh and 50 C on samples close to the oils. These experiments

were done in small l6-oz lotion jars having small openings to permit the

influx of air. In large unvented desiccators the reaction was less

severe. Some spots formed. Corresponding control samples without this

treatment formed no blemishes under the same conditions of temperature

and humidity.

Films were exposed to turpentine in large vented desiccators at room

temperature with the following results: 58 percent rh, general bleaching

in 35 days; ?6 percent rh, general bleaching and spots in 9 days; 90

percent rh, heavy yellow and red coloration, general bleaching, and

yellow spot formation in 4 to 5 days; 9? percent rh, considerable

general image bleaching but no spot formation in h days.

The effects of dipentene, pinene, and turpentine were comDared in

separate closed desiccators at room temperature and 90 percent rh. At

9 days the attack was about the same, with turpentine showing slightly

stronger attack.

Films were exposed to powdered rosin placed in culture dishes in

closed desiccators. At 85 percent rh and room temperature, heavy image

bleaching and a few spots were observed at 6 days and an increase in

14
bleaching and formation of reddish spots at 15 days. At 58 percent rh

and room temperature, weak general bleaching was found at 2 days and

considerable yellowing and many spots, including Type 3» at 5 days. A

(1)

gold treated sample showed slight yellowing at 5 days. Abietic acid,

the chief constituent of rosin, is known to form peroxide under certain

conditions of temperature and humidity.

The liberation of peroxides by the special grease, turpentine,

pinene, dipentene, and rosin was demonstrated by chemical tests.

3.9 Experiments With Cardboard

Rosin is widely used in paper making although the concentration may

be only a few percent. Cardboard may contain natural resins. Alum is

often added to papers, creating an acid condition favoring peroxide

formation. Measurable amounts of peroxide form in the natural aging of

commercial paper pulps and the peroxide formation rate is related to

fiber length. These facts strongly suggest that minute amounts of

peroxides generated in the aging degradation of the boxes in which the

film is stored can cause aging blemishes under some conditions.

To obtain further evidence on this point, microfilm was aged in

contact with cardboard from microfilm storage cartons. Cartons marketed

by five ma.jor American suppliers and one foreign supplier were used.

Both old and new cartons were used. Some films were clamped between two

pieces of cardboard. Others were stapled to the carton in such a way as

to hold the emulsion against the cardboard, the film strip running from

one side tab, down the side, across the bottom, and up the other side to

the tab. Some were stored in the presence of acetic acid vapor; others

were stored without acid.

15
Films were clamped between pieces of cardboard from film storage

boxes, and were placed in desiccators with acetic acid in the humidistat

solution. Many spots were formed at temperatures and humidities somewhat

above normal room conditions. Corresponding control samples without this

treatment formed no blemishes under the same conditions of temperature

and humidity.

Samples were placed in cartons so the emulsion lay against the sides

and other short samples were laid emulsion down on the bottom of cartons

in large desiccators. No acid was used. Spots were formed and some were

very similar to naturally occurring spots. Corresponding control samples

without this treatment formed no blemishes under the same conditions of

temperature and humidity. The tendency toward spot formation increased

with humidity, as would be predicted on the basis of the paper

degradation hypothesis. The effect of temperature was not as important

as the effect of humidity.

3.10 Effect of Density

In the laboratory studies of blemish formation, the dependence of

the tendency to blemish formation on density could be more readily

observed than it could be in field studies, since laboratory specimens

had step tablets on them. The results confirm the field observation.

For example, on a step tablet exposed to the very reactive grease, there

were no spots on the density steps 0.16 to 0.^4-3 but spots on density

steps 0.58 and above. The small density difference of 0.15 made the

difference between spots and no spots. The degree cf attack increased

with density at densities above O.58.

16
3.11 Effect of Gold Protective Treatment

(1)

Henn and Wiest proposed a gold protective treatment for microfilms.

The chemistry of their proposal appears theoretically sound. Microfilms

processed and treated with the gold protective treatment both during

processing and after processing, in a commercial microfilm laboratory,

have been studied. In all tests to date, the gold treated film has been

consistently more resistant than untreated film to general attack by mild

peroxides and has been virtually free of spot formation. The inertness

of the gold treated image is demonstrated by its resistance to a short

exposure to strong nitric acid. With severe and prolonged exposure to a

peroxide atmosphere, the gold treated material is affected and, under

these conditions, can even exhibit a resistance inferior to the untreated

material, but it is questionable whether tests of this severity are

pertinent to practice. Since this process has just been introduced

commercially, there is no background of practical experience.

k. Recommendations

One method of preserving records is to photograph them, producing

images of reduced size made up of silver dispersed in a gelatin film, and

to keep the film under conditions suitable for its preservation. This

method has been in use on a commercial scale for more than a third of a

century and is widely used in Government and industry. In recent years

it has been found that blemishes not previously noted developed on some

such films years after the films were processed and placed in storage.

We are attempting to determine the pertinent characteristics of the

photographic materials and the effects of various conditions on them.

Though research on these blemishes has not been completed, those now

1?
erifeoged in microfilming and those planning records systems for the future

have an immediate need for current information. Decisions with regard to

expenditures of resources for the preservation of private and public

records require value judgments based upon various considerations.

However, since some technical .judgments are involved, we offer the

following suggestions and recommendations based upon our recent findings,

past experience, and consultations with many people responsible for

microfilming and preservation of records in Government and industry. The

recommendations should be viewed in that perspective.

The blemish formation process, like all chemical processes, reauires

a combination of conditions. The elimination of one contributory factor

may prevent the formation of blemishes under a given set of conditions,

but we recommend, as a conservative policy, that all contributory factors

be avoided, insofar as it is practical to do so. The following

recommendations and suggestions are based upon this principle.

We recommend the use of film having a safety cellulose-ester base

meeting applicable raw stock requirements, the viscosity retention

requirement, and flexibility requirements of the American Standard

(5)

Specifications for Photographic Films for Permanent Records until that

standard is revised.

The observation that the incidence and severity of blemishes tend to

be greater on high density areas suggests that for archival ourposes it

would be desirable to use no higher density than is required to serve the

intended purpose, rather than strive for a high density for the sake of

appearance.

Throughout the exposing and processing operations it is important to

avoid scratching film, not only because scratches are undesirable in

18
themselves but because blemishes form along scratches.

Since the processing conditions establish the conditions of the image

and the gelatin, they play a role in establishing the probability of

attack. The contributions of all the various processing conditions are

not yet sufficiently well understood to warrant detailed recommendations

with respect to all aspects of processing. As noted in a previous section

of this paper, the addition of 0.2 g of potassium iodide per liter of

fixing solution, to fixing solutions not otherwise containing an

equivalent amount of iodide ion, appears desirable.

Long experience as well as the results reported here of the effects

of imbibed chemicals on microfilm support the conclusion that for archival

purposes, film should be thoroughly washed to remove chemicals remaining

after processing. Failure to do so invites general fading reactions and

spot formation.

Efficient removal of water droplets before drying greatly aids in

preventing deposition of chemicals on the film surface and promotes

uniform drying, with less tendency to introduce local variations in image

and gelatin characteristics. The nature of the drying process plays an

important role in establishing the characteristics of the gelatin layer.

The effects of time, temperature, humidity, and air velocity are not

sufficiently well known to allow us to make detailed recommendations, but

the facts presented here strongly suggest that great care be taken to

avoid dust, fumes of any kind, and gases other than those in normal clean

air.

We recommend that the American Standard Method for Determining the

Thiosulfate Content of Processed Black-and-White Photographic Film and

19
(12)

Plates be used until it is revised. We suggest the method of Pope

(9) as an improvement for a revised standard.

The provisions of the American Standard Practice for Storage of

(13)

Microfilm, with the few variations noted in this paper, should be

carefully observed.

The use of paper, string, adhesive tape, or rubber bands to bind the

roll introduces chemical and physical variables which should be evaluated

for each material. Such study may be justified if there is a real need

for the use of such materials.

Chemicals or materials employed in splicing operations should be

scrutinized carefully in light of the present findings. "Tie use of such

"foreign" materials can be avoided by the use of a thermally welded joint.

This method is in satisfactory use in a Government agency which is one of

the larger users of microfilm.

To avoid the peroxide generated in paper cartons and protect film

from gases and vapors originating elsewhere, it is suggested that rolls

of film be stored in sealed containers as defined in American Standard

(13)

Practice for Storage of Microfilm. Unpainted anodized aluminum

appears to be a desirable material. Hundreds of thousands of aluminum

cans and reels have been used by one Government agency and they have been

found practical and not too expensive. The reels were made of 0.051 in.

thick anodized 202*4- aluminum alloy and the cans were made of 0.032 in.

thick anodized 3003 aluminum alloy. The 202*4- duralumin alloy provides

the elasticity required for a reel to maintain its shape. Other materials

should be scrutinized carefully, in the light of our findings. In this

connection it should be borne in mind that spots were formed readily by

20
amounts of material too small to be detected by a mass spectrograph

-7 -9

which could detect amounts in the range of 10 to 10 moles.

T.ow temperature and humidity appear to be desirable storage conditions.

Tt is recommended that materials to be in inactive storage be placed in

the can in equilibrium with air at a relative humidity of 15 to 20 percent

at 50 to 60 F and that films for active files be placed in the can in

equilibrium with air at a relative humidity of 30 to 35 percent at 50 to

60 F. Tt is recommended that the storage temperature not be permitted

to exceed 70 F and that it be maintained between 50 and 60 F where

practical. Films may be stored at a lower temperature if they are warmed

sufficiently before opening to avoid condensation on opening the can.

Archival films should not be exposed to sulfur dioxide, hydrogen

sulfide, peroxides, ammonia, engine exhaust gases, or gaseous industrial

wastes. The fumes from turpentine, linseed- oil, or drying paints

containing such materials should also be avoided. To prevent fingerprints,

clean cloth gloves, available from dealers in photographic supplies,

should be used whenever film is handled. The film should be handled by

the edges, rather than the surfaces to avoid scratching the surfaces or

depositing dust. Film handling eauipment must be kept clean at all times

and should be inspected periodically for cleanliness and any condition

likely to scratch or otherwise damage film. Areas in which film is

handled must be kept as clean and dust free as practical operations permit.

Special air filtration and air washing may be required to avoid

objectionable air-borne contaminants. Since the gaseous decomposition

products evolved by nitrate-base film are very corrosive, such materials

should be removed from any building housing permanent records.

21
No aging blemishes have been observed on the information areas of

positive prints having dark characters on a nearly clear background,

although aging blemishes have been observed on the high-density borders

of one such film and others have been reported to us. For this reason the

retention of such positive films is a recommended procedure when additional

security is desired. A positive copy aopears to be the best choice when

only one film is to be retained in a permanent file and a nositive copy

will serve the intended purpose.

The orobability of loss of information can be very greatly reduced

by making more than one microfilm copy and preserving the conies in

separate places.

The only positive assurance that records are being preserved is

obtained by a regular program of inspection. This principle was

recognized in the American Standard Practice for Storage of Microfilm

(13)

adopted in 1957. Detailed sampling and insoection procedures are

(2)

outlined in NRS Handbook °6. Experience has amply demonstrated that

the routine satisfactory use of microfilms does not constitute adequate

insoection. The attention of the user is on the information rather than

the condition of the film and the optical nature of the blemishes makes

them difficult to detect in the routine use of film. Hndoubtedly there

will now be a keener awareness of the condition of the film on the part

of professional microfilm users, but systematic and well designed

sampling and inspection are still necessary parts of record preservation.

The sampling procedure should be regulated so that inspectors obtain a

different sample each time. Careful inspection of each stratum every two

years should reveal unsatisfactory conditions in time to allov appropriate

22
action to be taken. After a number of years, if no problems have been

encountered, this inspection period could be reasonably extended.

We recommend that existing collections of archival microfilm be

stored under the same conditions recommended here for new archival

microcopies. If the films have aging blemishes which appear to threaten

legibility, the information on the films can be preserved by copying the

films and preserving the copies.

Nothing in these recommendations should be construed to mean that

silver-gelatin type microfilm is the only possible material for archival

record storage or that the roll form is necessarily preferred. There

are, indeed, other possible materials but we have not conducted

sufficient studies of their properties to make recommendations with

respect to their use for the storage of records of permanent value.

This research was sponsored in part by the National Archives and

Records Service, the Library of Congress, the Social Security Administration, the Navy Bureau of Weapons, and The Adjutant General's Office

of the Department of the Army. In addition, the National Microfilm

Association solicited and secured financial support from the Bell and

Howell Company, E. I. T)u Pont De Nemours and Company, Dynacolor

Corporation, International Business Machines, Minnesota Mining and

Manufacturing Company, Recordak Corporation, and Xerox Corporation.

The authors wish to express their appreciation of the cooperation

of the sponsors and many other Government agencies who permitted access

to records, supplied old films for research, permitted inspections and

measurements to be made, and gave advice and helpful leads. A most

cooperative spirit was found in the laboratories of the film manufacturers.

Miss Anna-Mary Bush assisted in the preliminary inspections and

carried out the research on the Liesegang phenomenon.

2?
5. References

1. R. W. Henn and D. G. Wiest, Microscopic spots in processed microfilm:

their nature and prevention, Phot. Sci. Eng. 7, 253 (1963).

2. C. S. McCamy, Inspection of processed photographic record films for

aging blemishes, National Bureau of Standards Handbook 96, (U. S.

Government Printing Office, Washington, 1964).

3. J. P. Hill and C. G. Veber, Evaluation of motion--picture film for

permanent records, NBS Misc. Publ. 158 (1937).

4. American Standard Specifications for Photographic Films for Permanent

Records. Z3B. 3. 2-19^5 • (American Standards Association, New York).

5. American Standard Specifications for Photographic Films for Permanent

Pecords. PHI. 28-1957. (American standards Association, New York).

6. Federal Standard 125a, Federal StandardrFilm, Photographic and Film,

Photographic, Processed; (For Permanent Record Use), April 24, 1958.

7. C. I. Pope, Formation of silver sulfide in the photographic image

during fixation, J. Research NBS 64C, 65 (i960).

8. C. I. Pope, Stability of residual thiosulfate in processed microfilm,

Ibid, 67C, 15 (1963).

9. C. I. Pope, Determination of residual thiosulfate in processed film,

Ibid, 67C, 237 (1963).

10. R. E. Liesegang, Naturw. Wichschr. 11, 353 (I896).

11. A. Wexler and S. Hasegawa, Humidity- temperature relationships of

some saturated salt solutions in the temperature range 0° to 50° C,

J. Research NBS 53, 19 (1954).

12. American Standard Determining the Thiosulfate Content of Processed

Black-and-Vhite Photographic Film and Plates, Method for. PH4. 8-1958.

(American Standards Association, New vork^.

13. American Standard Practice for Storage of Microfilm. PH5. 4-1957.

(American Standards Association, New York).

24

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