JAIC 1991, Volume 30, Number 1, Article 5 (pp. 41 to 73)
PRESERVATION OF 19TH-CENTURY NEGATIVES IN
THE NATIONAL ARCHIVES
CONSTANCE McCABE
ABSTRACT—This article discusses an extensive project to preserve nearly 8,000 collodion
glass plate negatives of portrait and field work by noted photographers Matthew Brady,
William Henry Jackson, Timothy H. O'Sullivan, and others. Information is presented about
the constituents of collodion negatives and the characteristic deterioration related to inherent
compositional factors. Finally, preservation issues such as photographic duplication,
rehousing, and storage are addressed.
1 INTRODUCTION
SEVERAL SERIES of important 19th-century glass plate negatives in the holdings of the Still
Pictures Branch of the National Archives were selected for a major preservation project.
Negatives included in this project are from the following record groups: the Records of the
Office of the Chief of Engineers (RG 77). Records of the Geological Survey (RG 57). Records
of the Smithsonian Institution (RG 106), and Records of the office of the Chief Signal Officer
(RG 111), Nearly 8,000 negatives are involved in the project, ranging in size from 2 ½ × 3 ⅛
in to 18 × 22 in.
The Western Survey photographs, dating from 1867 to 1883, are among the first photographs
of the North American West. Many of the survey photographers are considered to be the most
accomplished of that time. Photographer William Henry Jackson worked under the direction
of Ferdinand V. Hayden documenting survey activities in Nebraska, Wyoming, Colorado,
Utah, Idaho, and Montana (1869–78).Timothy H. O'Sullivan and William Bell, under the
direction of George M. Wheeler, photographed explorations and surveys west of the 100th
meridian (1871–74). O'Sullivan also photographed for the Clarence King Survey of the 40th
Parallel (1868–70 and 1872). The negatives also include the work of John K. Hillers, E. O.
Beaman, and James Fennemore, all three of whom photographed under the direction of Jhon
Wesley Powell for the survey of the Rocky Mountain region (1871–78), and William R.
Pywell, who photographed the Yellowstone expedition of 1873 under the direction of Col.
David S. Stanley. The Western Survey photographs helped convince the federal government
to preserve some wilderness areas as national parks.
The photographs of the Matthew Brady1 Studio include views taken on the battlefields of the
American Civil War (1861–65), as well as portraits of notable Americans such as Abraham
Lincoln, Walt Whitman, Frederick Douglass, and Gen George A. Custer. Many of the images
were made by Brady's employees, including Alexander Gardner and Timothy H. O'Sullivan.
2 NEED FOR PRESERVATION
THESE NEGATIVES were acquired by the National Archives after its creation in 1934. They
are primarily collodion negatives, but the collections include some early gelatin plates and
copy negatives. Before coming to the Archives, they had been stored in a variety of
conditions, often in poor-quality enclosures within storage rooms lacking control of
temperature, relative humidity, or atmospheric contaminants. At the Archives they were
rejacketed, and reference prints were made available. For many years, however, the original
negatives, rather than duplicates, were used to make prints for researchers. This practice
resulted in frequent handling of the originals and placed the fragile glass plates at considerable
risk.
Custodial archivists and conservators observed other preservation problems associated with
these plates. These problems included flaking and softening of image-bearing binder and
varnish layers, image discoloration, and development of crystalline or moist deposits on the
glass support.
Of the plates involved in this preservation project, most remain in very good condition. All of
the negatives in these series have been examined and duplicated, and most have been newly
rehoused, topics addressed in later sections of this paper. The plates are stored in a specially
renovated storage area equipped with a self-contained air-conditioning system. Approximately
10% of these negatives require special preservation measures, such as custom housing for
broken or flaking plates.This project begain in 1983 and continues as resources are made
available for its completion.
Knowledge of the constituent materials of permanently valuable archival records is important
in determining proper long-term preservation measures. It is necessary to understand the
process by which they were made, the materials used in their production, and the manner in
which they deteriorate. This knowledge is expecially critical for the large group of historically
significant negatives in this preservation project.
The following discussion of the approach to preservation of negatives pertains to a relatively
large group of negatives made by the collodion process, all of which have significant
historical and artifactual value. Preservation projects that consist of a large or small number of
collodion or gelatin glass negatives may be approached similarly in small or large institutions.
The resources required to carry out a project of this scope are significant, however, and must
be justified by the value of the photographic records involved.
3 THE WET COLLODION NEGATIVE PROCESS
THE WET Collodion process was employed to create the Brady and Western Survey
negatives held by the National Archives. Introduced in 1851 by Frederick Scott Archer in
England, the collodion process was the forst practical negative system. The collodion negative
was ideally suited for use with the albumen printing process, which predominated during the
19th century. The collodion process was commonly used in the United States from 1855 until
about 1880, when the more convenient gelatin dry-plate negative became popular (Reilly
1986). The collodion process required the photographer to prepare a light-sensitive plate just
prior to exposure in the camera. Collodion is a solution of cellulose nitrate dissolved in ether
and alcohol. To prepare the plate, a glass sheet was carefully cleaned and flowed with a
viscous solution of brome-iodized collodion. To coat the collodion negative, the plate was
normally held at one corner between finger and thumb. The viscous collodion was poured
onto the center of the plate, which was then tilted so the plate would be evenly covered with
it. The excess collodion was then poured off the plate, usually from the corner opposite to that
which was held. The plate was then immersed in a bath of silver nitrate, which created the
light-sensitive silver halide. While still damp, the plate was placed in the camera for an
exposure that ranged from several seconds to several minutes. Once the collodion layer was
made light sensitive, only the areas that were coated and exposed to light would form an
image. Before it was allowed to dry, the plate was developed in an iron sulfate or pyrogallic
acid developer. The plate was then rinsed and fixed using a solution of potassium cyanide or
sodium thiosulfate, which left metallic silver as the final image material. The plate was again
rinsed with water and, when dry, was varnished to protect the easily abraded collodion layer.
4 IDENTIFICATION OF COLLODION NEGATIVES
TO PROVIDE appropriate care it is of fundamental importance to recognize the process by
which a glass plate negative was made. Collodion negatives have occasionally been
misidentified as gelatin dry plates. While the fundamental approach to preservation of glass
negatives is the same for collodion or gelatin negatives, conservation treatment approaches
differ significantly depending on the nature and extent of deterioration. Factors to consider
(and not to consider) when attempting to differentiate collodion from gelatin glass plate
negatives include image color, image appearance, surface character, and plate thickness.
4.1 PLATE THICKNESS
All very large collodion plates and many smaller collodion negatives were made on relatively
thick glass (5/32–3/16 in) because it does not break as easily as thin glass. Most plates are
approximately ⅛ in thick; rarely do they exceed ¼ in. A few small negatives in the holdings
of the National Archives are only 1/16 in thick, and most are approximately the same
thickness as gelatin plates of comparable size (Witkin and London 1979, 34). Glass thickness,
therefore, cannot be considered an important factor in isolating collodion from gelatin
negatives.
4.2 IMAGE COLOR
The appearance of a negative will differ according to the combination of chemical processing
steps employed in its creation. For example, when viewed in reflected light, a collodion
negative developed with iron sulfate and fixed with potassium cyanide will appear lighter in
color than one developed with pyrogallic acid and fixed with a thiosulfate fixer (“hypo”),
which appears black (Towler 1879, 121; Archer 1854, 36, 39). Other steps in the processing
of collodion negatives often included intensification and occasionally reduction, which also
affected the final image color (Towler 1879, 124; Lea 1871, 169, 171–77; Lavedrine and
Garnier 1989). These differences in processing have caused confusion among photographic
historians. Collodion negatives have been described as appearing “creamy or milky in color”
(Coe and Howarth-Booth 1983, 13)2, “light tan or gray” (Weinstein and Booth 1977, 715),
“dull tan” (Gill 1978), “typically brownish yellow and highly reflective” (Eastman Kodak Co.
1979, 57), and “brown-black in the shadows and cream in the highlights” (Rempel 1979) in
reflected light. These descriptions of collodion negatives are only partially accurate.
Approximately 40% of the collodion negatives in the holdings of the National Archives are
quite black and neutral in hue. It is possible that custodians of collodion negatives have
mistaken black-colored collodion negatives for gelatin dry plates of original collodion
negatives for duplicate negatives. Collodion negatives may appear in the colors described
above as well as olive green, brick red, and lemon yellow or combinations of several colors on
one plate.
Caretakers of photographic negatives must remember that gelatin negatives may also be found
in a variety of image colors. In fact, gelatin negatives are occasionally found that resemble
ambrotypes (fig. 1). While the color of a plate is an important factor in identifying the process
by which glass negatives were made, the color of a plate alone must not be considered the
determining factor. Accurate dating, image appearance, and surface character are also crucial
for identification of the negative process.
Fig. 1. Two negatives that resemble ambrotypes , both seen in reflected light on a dark background. Above: A
three-image collodion plate of Abraham Lincoin by the Matthew Brady Studio (RG 111-B-3658-C). Below: A
gelatin dry plate portrait with a light-hued image (RG 19N-46-21-21).
4.3 IMAGE APPEARANCE AND SURFACE CHARACTER
To isolate black-colored collodion negatives from gelatin dry plates, the plate edges and
corners where there is image density (dark areas) should be examined. A gelatin plate will
generally have a very straight, regular, and even surface along the edge due to its production
by machine. Evenly fogged image silver along the edge may also be a clue that the plate was
coated by machine, especially if the fogging is not related to the photographic image (fig. 2).
The evennes of coating is a relative matter, and while gelatin plates are nearly always coated
evenly, gelatin along the edges may lift during handling or processing (fig. 3) or as a result of
deterioration. The image along the edges of a collodion plate will only rarely be uniform,
indicating that the image-bearing layer was coated by hand (figs. 4–5). Other physical
characteristics, such as fingerprints in the image at corners or at edges, provide additional
evidence that the plate was coated by hand (figs. 6–7).
Fig. 2. The corner of a gelation dry plate generally has a smooth and even surface along the edge, indicating an
emulsion coated by a machine. The even fogging of image silver along the edge of the binder indicates
regularity in binder coating (RG 57-PS-46).
Fig. 3. Another gelatin dry plate shows primarily even edges. Slight irregularities are ofter found, due in part to
handling during chemical processing (RG 19N-46-21-19).
Fig. 4. The corner of a collodion negative exhibits various types of unevenness, such as this irregularly handcoated plate (RG 77-KW-21).
Fig. 5. In this detail of what should be an even-toned sky area, the irregular collodion application is evident (RG
106-WB-88).
Fig. 6. Collodion plates usually exhibit at least one corner with a fingerprint (RG 111-B-280).
Fig. 7. Another collodion plate with a finger print in one corner (RG 57-PS-559).
A common misconception regarding the appearance of collodion negatives involves their
surface character. Confusing the thin, smooth, and virtually two-dimensional collodion layer
with the relatively thick and often uneven varnish coating, authors have given descriptions
such as, “The emulsion coating layer is often uneven and in raking light shows swirls, thick or
thin areas” (Witkin and London 1979, 34).3 Another description states, “Since the collodion is
flowed on by hand, it often shows tidal marks and varying thickness” (Eastman Kodak Co.
1985).4
The uneven “swirls, thick or thin areas” described above actually describe not the collodion
binder layer but the varnish layer that coats the binder. When viewed by the naked eye in
raking light, an unvarnished negative will appear smooth and matte surfaced. The unvarnished
collodion binder layer is quite thin and, except along the plate edges, two-dimensional in
appearance. Some collodion plates do exhibit varying degrees of density due to uneven
coating. This type of image irregularly is often seen in large, even-toned areas, such as the sky
in landscape views (figs. 4–5, 9–10). These unevenly coated plates, however, do not show
associated three-dimensional ridges (figs. 4–5, 8–10).
Fig. 8. Striations in what should be an even-toned sky area seen in a collodion plate (RG 106-WB-272).
Fig. 9. Image irregularity in the sky area due to uneven coating by hand (RG 57-PS-464).
Fig. 10. A print from the same collodion negative as shown in figure 9 (RG 57-PS-464).
A varnished glass negative will usually show uneven surface characteristics not visible on an
unvarnished plate. This three-dimensional surface appearance is due primarily to the relatively
thick varnished layer and should not be confused with the binder layer beneath. These threedimensional ridges, or “flow marks,” of the varnish on the surface of the plate can be present
on gelatin as well as collodion negatives (figs. 11–15). The varnish surface is usually rather
glossy, but it may be matte. Although virtually all collodion negatives were varnished for
protection from abrasion, the varnish layer may be quite thin and difficult to see with the
unaided eye. Since the surfaces of some collodion and gelatin negatives may look similar,
they are difficult to distinguish by surface characteristics alone. Occasionally an unvarnished
or a partially varnished collodion negative will be found. Unvarnished collodion negative
surfaces (whether image silver is present or not) will normally appear quite thin, smooth, and
abraded when compared with varnished collodion plate surfaces (figs. 16–23).
Fig. 11. Three-dimensional ridges of the varnish layer seen on a collodion plate (RG 57-PS-54).
Fig. 12. Another example of three-dimensional varnish “flow marks” seen on a collodion negative (RG 57-PS536)
Fig. 13. Three-dimensional ridges seen on a varnished gelatin dry plate negative (RG 57-PS-120)
Fig. 14. Another gelatin dry plate negative illustrating three-dimension al ridges (RG 19N-46-21-19)
Fig. 15. An unvarnished gelatin dry plate (RG 57-PS-33)
Fig. 16. A collodian negative with only the left portion varnished, seen in transmitted light. Note the severe
abrasion on the side not protected by varnish (RG 111-B-4998).
Fig. 17. A detail of the same collodion negative shown in figure 16. seen in reflected light on a light colored
background.
Fig. 18. A print from the same detail of the collodion negative shown in figures 16–17
Fig. 19. Seen at an oblique angle, the same partially varnished collodion negative shown in figures 16–18
Fig. 20. A varnished gelatin dry plate negative seen in transmitted light. Note that the top corners are not
varnished (RG 19N-48-21-21).
Fig. 21. A detail of the same gelatin negative shown in figure 20, reflected light on a light-colored background.
Fig. 22. A print from the same detail of the gelatin negative shown in figure 20–21. Note the lack of abrasion in
the unvarnished area.
Fig. 23. Seen at an oblique angle, the same partially varnished gelatin negative shown in figures 20–22.
The difference between collodion and gelatin negatives on glass can often be quite subtle; it
takes experience and practice to become proficient in identifying collodion negatives. Various
chemical processes were employed to create these negatives, and deterioration may have
taken place over time. The effects of these and unknown factors give the negatives image
appearances that may be difficult or impossible to explain. To generalize about the appearance
of collodion and gelatin glass plate negatives is not possible, as both can have similar
characteristics that may make differentiation confusing. It should be noted that unless
deterioration is evident, preservation of both negative types requires similar approaches.
5 CONDITION AND DETERIRATION
THE PHYSICAL fragility and chemical complexity of the component structure of glass plate
negatives combine to create complicated preservation problems. The many variations of
formulas used by the photographers for sensitized collodion, developers, flxers, postprocessing treatments, and varnishes, as well as the types of glass employed, pose difficult
questions for the preservation needs of these collections.
5.1 GLASS DETERIORATION
The moisture-related deterioration of the glass component of some negatives was a major
factor in the decision to undertake a large-scale preservation project at the National Archives
aimed at arresting further damage to these valuable photographs. Until recently, glass had not
been considered a factor in the deterioration of photographic plates. However, some glass
negatives at the National Archives underwent changes in their physical character, evident as a
crystalline or slippery deposit on the nonimage side of the plate and as binder and warnish
lifting and/or softening on the image side of the plate. These changes are associated with
variations in environmental conditions. When the relative humidity in the storage environment
is dry, surface deposits on the nonimage side of the plate appear crystalline; at higher relative
humidity, the deposits appear moist (figs. 24–26). These observations, as well as literature
with alarming statements about the chemical instability of some glass types, indicate that
some glasses produced during the 19th century are chemically unstable and that some 19thcentury negatives were made with glass that has deteriorated (Segal et al. 1976; Simpson
1958, 1959; Brill 1978; Barger et al. 1989).
Fig. 24. Detail of a secondary glass support for a pair of glass plate stereo negatives seen on a dark background,
illustrating the crystalline deposits associated with glass deterioration.
Fig. 25. Detail of the same secondary glass support shown in figure 24 after exposure to high relative humidity.
The deposits are now difficult to see, as they are clear and colorless droplets.
Fig. 26. Another form of surface deposit seen on glass-supported 19th-century negatives is a slippery haze. The
nonimage side of this negative is seen in reflacted light on a dark background. The dark, dendritic area is the
glass, and the surrounding lighter-toned area is the hazy surface deposit (RG 106-WB-293).
The collodion and varnish layers of plates that exhibit surface deposits on the nonimage side
of the glass supports, as described above, characteristically develop some degree of softening,
lifting, or flaking (figs. 27–30). The hygroscopic nature of the salts associated with glass
decomposition (Moser 1961) can also contribute to silver image deterioration (Barger 1985),
which is seen in a number of negatives in the holdings of the National Archives as localized
fading or staining (figs. 31–32). Negatives that do not exhibit visible glass deteriorationrelated surface deposits are generally in very good conditions.
Fig. 27. An example of damage caused by softening of the binder and collodion layers in a collodion negative
with deterioration of its support glass (RG 106-YX-10)
Fig. 28. Another collodion negative suffering from softening and flaking associated with glass deterioration
(RG 111-B-3879)
Fig. 29. A collodion negative exhibiting severe flaking, again associated with glass deterioration (RG 111-B5664)
Fig. 30. The collodion and varnish layers of this negative are lifting in a manner similar in appearance to a
deteriorated cellulose acetate negative (RG 77-KN-153).
Fig. 31. Localized fading is usually accompanied by staining in plates that exhibit severe glass deterioration, as
illustrated in this collodion stereo pair (RG 11-B-5653). At the time of its creation the two-image plate was cut
in half and mounted to a secondary glass support to facilitate production printing.
Fig. 32. Another collodion negative with surface deposits associated with a deteriorated primary glass support
exhibits spotty fading and staining around the edges. Fadind and staining are also seen along a meandering
cracking pattern of the binder and varnish layers of this deteriorated plate (RG 77-KW-16).
These observations led the National Archives Research and Testing Laboratory to carry out
tests to confirm that the surface deposits on the 19th-century glass were, in fact, caused in
large part by the deterioration of the glass supports. The secondary glass supports to which
stereo negatives were attached date from the period during which the negatives were made.5
These secondary supports were used as test specimens (figs. 24–25); other test specimens
included portions of dispensable collodion negatives in various conditions. The samples were
analyzed in an attempt to determine the role of glass deterioration in the degradation of 19thcentury negatives.
Surface deposits from the secondry-support glass plates were rinsed with distilled water into
sample cups for analysis by x-ray fluorescence. A blank was similarly prepared but by rinsing
newly made window glass into the sample cups. With titanium being used as the target, the
presence of silicon in the surface deposit was confirmed. No silicon was detected in the blank.
There is no obvious source of silicon other than the glass itself, therefore it appears that the
glass is chemically unstable and plays a role in the deterioration of the negative.
An attempt was made to quantify the silicon present in the surface deposits of a deteriorated
secondary support (one sample) and in the varnish and binder layers of 19th-century plates in
both good condition (one sample) and poor condition (two samples) and in a blank consisting
of any surface deposits of a piece of newly made window glass. The samples were prepared
for analysis by rinsing the surfaces of the secondary support, the negative shards, and the
blank with acetone and distilled water onto polyester film and allowing them to evaporate.
The sample were then dissolved in a 70% solution of nitric acid and analysed using a PerkinElmer Model 2100 atomic absorption spectrometer (with a 2% standard deviation and a
detection limit for silicon of 0.08 ppm). No silicon was detected in the blank, but silicon was
detected in all other samples, in quantities ranging from 0.01 ppm to 1.42 ppm. However, no
correlation could be made regarding the quantity of silicon as it relates to deterioration. The
lack of correlation appears to be due to the small sample size involved (non uniform surface
area of less then 2 × 2 cm), which made weighting the samples difficult. This prelimlnary
investigation suggests that a more thorough study should be undertaken, with a more easily
measurable and larger statistical sampling, to understand better the role of glass deterioration
as it relates to collodion negative preservation.
5.2 STABILITY OF OTHER COMPONENTS
The final image of a collodion negative is composed of very small particles of metallic silver.
This silver image is susceptible to oxidative deterioration, which appears as fading or
discoloration. Silver image deterioration may be caused by many inherent problems, such as
poor original chemical processing, or by unstable constituent materials. External factors may
also lead to or exacerbate image deterioration. These factors might include storage in an
environment with atmospheric pollutants or elevated RH. Exposure to other oxidative sources,
such as poor-quality storage enclosures, may also cause image deterioration. It may be
difficult to determine the specific cause of deterioration in a 19th-century negative if the
method of production and use and storage history of the plate are unknown. Much research
has focused on the problems of silver image stability, and further discussion of this subject is
beyond the scope of this paper.
Collodion, the binder within which the silver particles are suspended, is composed of cellulose
nitrate. Motion pictures and still photographs created on cellulose nitrate supports are known
to be chemically unstable and, if not properly stored, will deteriorate over time. It has been
speculated that collodion negatives, especially those that are vernished, are as unstable as
negatives with a cellulose nitrate film support (Gillet et al. 1986). The condition of the
negatives at the National Archives suggests, however, that the cellulose nitrate layer is less a
factor in the deterioration of collodion negatives than is the glass used in their production.
Cellulose nitrate is still used in today's photographic industry as an extremely thin adhesive
subbing for some gelatin photographic films and modern plates. Although substitutes have
been found for cellulose nitrate for the purpose of adhering gelatin to plastic or glass supports,
little evidence exists that photographs with cellulose nitrate subbings are considerably less
stable on account of the subbing (Ram and McCrea 1988; Brems 1988).6 It does not appear
that the collodion layer has posed a significant preservation problem for the 19th-century
negatives at the National Archives.
The varnish formulations used to protect collodion negatives from abrasion are very similar to
those employed in painting. Naturally occurring resins such as copal, dammar, sandarac, and
mastic were usually dissolved in alcohol or benzine and applied to a warm negative.
Photochemical deterioration associated with vernished paintings, such as yellowing, does not
seem to be a serious factor in negative deterioration. Collodion negatives were made to be
used by the printing-out process, during which they are subjected to intense sunlight. For the
most part, negatives are stored in the dark, and few plates exhibit considerable damage that
can be attributed to exposure to light. The varnishes used with collodion negatives were
chosen for their resistance to abrasion and to damage from exposure to strong sunlight. Other
properties of vernishes, however, may have preservation implications. As with many
components of archival records, the varnish is susceptible to damage from poor storage
conditions. Fluctuating temperature and relative humidity can lead to the degradation of the
varnish layer, seen as cracking, lifting, and flaking. When combined with the decomposition
products from the glass support, the vernish layer can become very soft and vulnerable to
phyalcal damage. The damage associated with the varnish layer can lead to degradation of the
underlying collodion layer and the silver image.
6 PRESERVATION OF COLLODION NEGATIVES
BASED ON an understanding of the collodion negative's component materials, causes of
deterioration, and research needs, the National Archives developed a large scale program to
care for its 19th-century negatives. The primary preservation objectives involved in this
project are: cleaning the negatives, removing tape from them as appropriate, duplicating them,
rehousing them, and storing them in appropriate cabinets and facilites. Instructions for those
engaged in the project are:
1. Survey the negatives for sizes, numbers, and condition. Determine the sizes and
number of plates to be stored on each shelf. Weigh the plates in preparation for
specifying shelving load requirements. Estimate the number and sizes that will require
special housing. Based on the above information, order shelves.
2. Examine each plate sequentially; carefully document condition, size, and appearance;
clean, rehouse, and reshelve, notion location. Plates in poor condition that must be
segregated for special housing and storage should be set aside at this time.
3. Working with one plate at a time, remove tape as appropriate and construct sink mats
for plates in poor condition. Once all plates in poor condition have been housed in sink
mats, shelve or box sink-matted plates sequentially according to size of enclosure
(small plates broken into many pieces may require a larger enclosure than a larger
plate broken into only two pieces).
4. Once all plates are cleaned and rehoused, duplicate sequentially and according to size.
5. Store originals, interpositives, and duplicate negatives in separate, environmentally
controlled locations. Use duplicates to make prints; use interpositives to create new
duplicates as required; and retire originals from use.
6.1 CLEANING
The image side of a collodion plate is extremely sensitive to moisture and to organic solvents.
Despite claims that collodion negatives may be safely cleaned (Ostroff 1976; Rempel 1987,
84),7 tests carried out at the National Archives indicate that damage is likely to result from
attempting to clean tha image side of the plate with water based on with most organic solventbased cleaners. Washing collodion plates can be very damaging and should not be attempted.
Because of the collodion negative's sensitivity to cleaning, only a soft-hair brush may be used
to dust the image side of the plates and only when the condition of the plates (no flaking or
softening) allows for safe dusting.
Surface dirt on the nonimage glass side, if not cleaned away, will be visible in duplicate
negatives. Concern has been expressed, however, about the possibility of accelerating
deterioration of the glass by the use of cleaning solutions on the glass side of the plate (Moser
1961; Simpson 1959). Tests were made to determine if cleaning the glass side would be safe
and, if so, to select a cleaning solvent. A range of solvents, including commercially available
glass cleaners, water, alcohol, acetone, and acidic and alkaline aqueous solutions, were tested
on both deteriorated 19th-century glass and on modern, comparatively stable, window glass.
Samples were aged in a cycling oven (room temperature and RH to 50°C and 95% RH daily
for 15 and 30 days). Deterioration was induced in all samples, with more severe deterioration
seen consistently in all 19th-century samples. No cleaning solution was isolated as superior,
and no cleaning solution performed noticeably better than water.
Despite inconclusive test results, a decision was made to clean all nonimage glass surfaces of
the negatives with detonized water, since a primary preservation goal is to create duplicates of
the highest possible quality with the greatest amount of retained information. Such duplicates
can be produced only with negatives that are as clean as possible. By retiring the originals
from use and storing them in an environmentally controlled area, it is hoped that further
deterioration of the plates will be arrested. In this way the best balance between preservation
and the needs of researchers can be achieved.
6.2 TAPE REMOVAL
Before these negatives were acquired by the National Archives, a number of broken plates
were mended with verious adhesive tapes. Some of these mends apparently date from the 19th
century and employed gummed paper tape. Twentieth-century tapes included pressuresensitive cellophane tapes and several types of opaque masking tapes. Fortunately, only a few
plates had adhesive applied to their image side.
In order to reproduce as such image information as possible from these taped plates,
uninscribed mending tape was removed from the glass side. No labels, masks, tapes, or
attachments with potentially historical significance were removed, however, nor were any
other original elements of the artifact removed, such as retouching or other unusual
components of the negatives.
Tape removal was carried out with great care, as this operation usually required manipulation
of the plates while placed face down on smooth paper. For plates with binder or varnish
deterioration, the edge of the glass was supported while the tape was removed.
The procedure for tape removal involved first cutting the tape along the edges of breaks. Once
the plate was separated into individual pieces, the tape was mechanically peeled or scraped
away. Residual adhesive was removed with an appropriate solvent such as water, ethanol, or
acetone, applied locally with a cotton swab. Care was exercised to avoid contact of the solvent
with the image side of the plate, since the binder and varnish layers are often readily soluble.
Because of this solubility, special care was taken with plates containing tape on the image
side. Where the carrier and adhesive of the tapes could be removed from the image side
mechanically and without the use of solvents, the tape was removed. More tenacious tapes on
the image side have not yet been removed.
Problems related to reversibility and optical properties of adhesive repairs of glass have
resulted in the decision to assemble the broken negatives in their proper orientation during the
duplication step and not to repair them. Adhesives presently employed to repair glass objects
are primarily organic polymers, including synthetic polyester, epoxy, polyvinyl alcohol and
acrylic resins, and cellulose nitrate. Silicones and silance are also used in glass conservation.
However, if a collodion negative were repaired with any of these adhesives and it became
necessary to reverse the adhesive, it would be diffcult to do so. Capillary action of liquids
between glass joints is difficult to control while applying adhesives or solvents and could
threaten to dissolve the image bearing layer. Therefore, rather than repairing the broken
negatives, they have been rehoused as described below.
6.3 DUPLICATION
The image in 19th-century negatives differs significantly from most modern film negatives.
They were made to be printed onto a printing-out paper such as albumen paper (Reilly 1979).
Negatives used in printing-out systems are exposed in direct contact with the photographic
paper. The printing out paper darkens spontaneously when exposed to light, creating a print
the same size as the original negative. The negatives employed for the printing-out process are
longer in tonal range and often higher in contrast than are most modern film negatives. The
characteristics of 19th-century negatives make them capable of producing excellent printedout prints. Difficulties are encountered, however, when these negatives are printed onto
modern developing-out papers.
Modern developing-out papers require chemical development to produce an image. When
10th century negatives are printed onto developing-out papers, image detail is often sacrificed.
The negatives required for use with developing-out papers have a relatively short tonal range,
but because modern negatives and photographic papers have been manufactured to be used
together, the results can be comparable to the excellent image quality of printing-out systems.
In order to produce prints that retain maximum image quality, a two-step interpositiveduplicate negative system was selected to preserve these negatives photographically (Munson
1982). This two-step process produces two sets of images from the original glass plate:
interpositives and duplicate negatives. First, two interpositives are made by contact printing
the negative onto film. One sheet is exposed to reproduce all highlight, middle tone, and
shadow detail, matching the entire tonal range of the original plates (fig. 33). Another sheet is
then exposed to create a positive “shadow mask,” which is a high-contrast rendering of only
the shadow detail (fig. 34). The shadow mask is required to create a duplicate negative of
complete tonal range and to compensate for factors related to modern film manufacture,
exposure, and processing. After processing, these two interpositives are placed in register,
and, as the name indicates, the image appears as a positive. These two interpositives are then
exposed in register onto another sheet of film. With this system, a duplicate negative of
extremely high quality is created (fig. 35). Careful selection of film type, along with control of
exposure and processing, allows the photographic technician to produce a duplicate negative
that can easily be printed onto modern developing-out papers. A duplicate negative made with
this system allows production of prints with exceptional quality and tonal reproduction that is
comparable to pristine printed-out prints from collodion negatives (fig. 33).
Fig. 33. The iamge of an interpositive on film appears very similar to the final print (RG 57-PS-484).
Fig. 34. The interpositive's “shadow mask” is a high contrast rendering of only the shadow detail of the image
shown in figure 33.
Fig. 35. The duplicate negative of the image shown in figure 33.
After being processed according to archival specifications, inspected for quality, and jacketed,
the interpositives are segregated from the duplicate negatives. The duplicate negatives are
stored in the stack area and used by the photographic laboratory as prints are requested. For
archival security, the interpositives are stored separately. The interpositives are considered the
archival record and are used only when another duplicate negative is needed. The original
plates are retired from use.
6.4 REHOUSING
Photographic negatives must be housed in enclosures that will protect them from physical and
chemical damage. For these glass negatives, two types of storage systems have been designed,
based on their condition. For plates in good condition, a vertical storage system is used. Plates
in poor condition—with flaking, lifting, or softening of the binder of varnish layers of
breakage of the glass support—are stored horizontally and protected individually with paper
enclosures.
The paper enclosures used in this project had to meet rigid specifications to ensure the
suitability of the papers and adhesives for housing collodion negatives. Analytical tests were
conducted to determine pH, alkaline reserve, reducible sulfur and lignin content, and sizing
agent used. Accelerated aging was carried out with modern photographic materials incubated
in contact with storage enclosure materials to further aid in the selection of proper storage
materials (ANSI 1986).
Seamless four-flap paper enclosures have been produce in various standard sizes for the
storage of plates in good condition. These enclosures allow the user safe access to the plate by
unfolding the flaps rather than by sliding it out of the sleeve while grasping it between finger
and thumb. Because deterioration of silver images has been associated with adhesive seams,
no adhesive has been used to fabricate these enclosures. It is hoped that these four-flap
enclosures will prevent image deterioration associated with adhesive seams (fig. 36).
Fig. 36. A glass plate negative and its seamless four-flap enclosure
These enclosures are used for plates of standard size, plates slightly smaller than the closest
standard size, and those with small corner or edge losses. A sheet of thin rigid paperboard the
full size of the enclosure is inserted for additional support for those plates that are smaller than
the size of the enclosure. Negatives in good condition are stored vertically, on the longer plate
edge, on shelves with metal dividers the full size of the plates. Four to five plates are stored
between each pair of dividers (fig. 37).
Fig. 37. Negatives stored vertically within four-flap enclosures on shelves constructed with rigid dividers
Sink mats have been constructed in several standard outer dimensions for the protection of
damaged negatives. These enclosures are made of high-quality materials, including corrugated
paperboard, mat board, and smooth bond-weight paper, with acrylic pressure-sensitive tapes
used for assembly. Care is taken to assure that no adhesive is applied near the plate. These
sink mats are designed to give rigid horizontal support. The high-quality corrugated
paperboard cover does not come in contact with the image side of the negative because the
walls of the sink mat are built slightly higher than the thickness of the plate within and a paper
interleaf is placed between the plate and the sink mat cover. If a negative exhibits softened of
flaking binder and varnish layers, the interleaf is attached to the inside cover with adhesive
and the sink mat is constructed with extra wall height, thus preventing contact of the enclosure
with the vulnerable negative.
The broken negatives are assembled in proper orientation for duplication but are housed in
sink mats with the components separated with paperboard spacers attached with adhesives to
avoid mechanical damage to the glass pieces (figs. 38–39). Each problem plate requires
individual attention; its enclosure is constructed to meet its special needs, and each sink mat is
custom made.
Fig. 38. A broken negative housed within a custom-made sink mat construced with a paper tab to assist in
lifting out the large piece. These enclosures must be carried horizontally or the glass will slip away from its
support.
Fig. 39. A broken negative in a sink mat. No pieces are missing. The pieces are spaced with photographicquality mat board attached to the base of the enclosure with adhesives. The negative was pieced together for
duplication.
Negatives housed in sink mats are stored horizontally in stacks of three to six (depending on
size and weight) within storage boxes. Boxes are of the drop-front style with metal stays. If
safe to do so, two or three boxes may be stacked on each shelf. Each box is marked with the
cautionary label, “Coution: Broken Glass. Carry Horizontally” (fig. 40).
Fig. 40. Boxes of sink-matted negatives shelved with the label, “Caution: Broken Glass. Carry Horizontally.”
A decision was made not to seal broken or flaking negatives within a glass “sandwich” as this
kind of protective package, where the glass is tightly enclosed, can produce corrosion in
chemically unstable glass (Barger et al. 1989). To avoid the possibility of accelarated
deterioration of a glass negative within such an enclosure, unstable plates are enclosed in
paper sink mats.
6.5 STORAGE
The preservation of archival records demands that everything meant to protect them be
selected cautiously. Not only must the materials that come in close contact with records be of
the highest possible quality, but the larger environment must also be regulated to ensure the
preservation of permanently valuable holdings. Because of the fragility of these glass plates,
and their sensitivity to the environment the stall at the National Archives developed detailed
specifications not only for storage enclosures, but for storage cabinets, materials used to
renovate the storage room, for fire suppression, and air quality.
A major concern was the choice of available paint finishes for storage cabinets.
Environmental contaminants, such as volatiles associated with inadequately cured alkyd oilbase paints, have been showen to cause silver image delertoration (Feldman 1981), Steel
cabinets finished with baked enamel have long been recommended for storage of
photographic materials, since it is commonly believed that the baking process ensures
thorough curing of the finish and always eliminates potentially harmful paint volatiles, such as
peroxides and organic solvents (Time-Life Books 1972). Thus steel cabinets with a baked
enamel finish were custom made for this project.
The National Archives had difficulty procuring a type of cabinet with a paint finish that met
its specifications. Cabinets in the first shipment arrived with a strong odor of paint solvents
indicative of inadequate curing during the baking process. As specifications limited the
allowable valatiles, the cabinets were sent back of the manufacturer to be rebaked. This
experience alerted the Archives to the possibility of improper curing procedures during the
manufacture of painted cabinets. It is critical that the baking process eliminate potentially
damaging volatiles and that measures be taken to ensure thorough curing of paint finishes.
There is need for further testing of paint films to determine their sultability for storage of
archival records. At this time, the Archives is investigating other finishes, such as powder
coating, for future use with photographic materials and other permanently valuable records.
Two basic cabinet designs have been fabricated, one for horizontal storage and the other for
vertical storage. In the vertical storage cabinets full-size rigid dividers are placed at 1 inch
intervals. Each space can accommodate several negatives, and each shelf up to 100 plates.
Depending on the size of the plates, and the number and sizes of plates to be placed on each
shelf, different weight load specifications were required.
All cabinets are constructed with locking doors, and six air vents provide for ventilation. The
doors and venta of the cableneta are sealed with allcome rubber gaskets. The seals provide
assurance that, in case of ceiling leaks, water will not seep into the cabinets Locking devices
and shelf brackets are nickel plated.
A room was specially renovated for the storage of photographic holdings of high intrinsic
value, including these 19th-century negatives. The room has been equipped with a selfcontained air-conditioning system that filters and purifies the air and controls the temperature
and relative humidity (65°F and 35%–40% RH). Fluorescent light fixtures are equipped with
ultraviolet filters. Fire suppressant systems include Halon (a cholorofluorocarbon) with a dry
pipe water extinguishing backup. The National Archives is eagerly awaiting development of
an environmentally safe substitute for Halon that meets the standards described in the
Montreal Accord, an international agreement that will prohibit the use of halogenated
hydrocarbons that adversely effect the ozone layer. The walls, cellings, and fixtures in the
photographic storage room have been finished with water based latex acrylic paint, and the
floor is covered with a nylon carpet. Since no carpet padding was commercially available that
met the Archives's requirements for chemical inertness, none was used. The seams of the
carpet were attached with a silicone heat seal, and the carpet was tacked to the concrete floor
with concrete nails.
7 CONCLUSION
THE NATIONAL ARCHIVES continually seeks to develop the best means to preserve its
photographic records. Much recent work has been devoted to understanding the nature and
needs of 19th-century negatives. During this work records were kept of the appearance and
condition of these negatives and of the materials and methods used for their care. The
Archives staff plans to monitor further changes in these negatives and to investigate the
causes of such changes. Should new and safe methods be discovered to reverse existing
damage, these methods will be considered. The staff at the National Archives hopes that
future generations will find the records of the preservation approach valuable and the
decisions sound. We also hope that our work will benefit other institutions and individuals
responsible for the safekeeping of our photographic heritage.
ACKNOWLEDGEMENTS
THIS PHOTOGRAPHIC preservation project involved the collaborative efforts of the
archival staff of the Still Pictures Branch, conservators, photographic technology specialists,
conservation scientists, facilities engineers, and a supportive administrative staff.
I wish to thank many people who have contributed to the success of this project and to the
completion of this paper: Mary Lynn Ritzenthaler, Debbie Hess Norris, Ed McCarter,
Elizabeth Hill, Doug Munson of the Chicago Albumen Works, Susan Lee-Bechtold, Karen
Garlick, Beth Napier-Cain, Ramanathan Panayappan, Nora Kennedy, Janet Shrenck, David
Salisbury of Perkin-Elmer Corporation, Doug Severson, Kenneth E. Harris, Peter Liebhold,
Mary McCabe, Neal McCabe, Bobbye West, Norvell Jones, Susan Barger, John Collins,
Nancy Reinhold, James M. Reilly , Allen Johnson, Holly Reed, Tim Bradley, Carrie Beyer,
Frank Hengemhle, Chandru Shahani, and the staff of the Still Pictures Branch.
NOTES
1.. An original petition of Matthew B. Brady, in the custody of the National Archives,
requests that Congress purchase his collection of Civil War photographs. In this document,
which bears his signature. brady's given name is spelled “Matthew” (with a double “t”). While
his given name is constantatly spelled with only one. It means thousands in the article to
follow the spelling. Brady's petition.
2.. Coe and Haworth-Booth also describe albumen negatives as “creamy or milky” in color.
When they usually appear reddish brown in hue.
3.. The term “emulsion coating” seems to describe the varnish layer. However, gelatin plates
may be varnished with uneven coatings as well.
4.. This description may be considered accurate from a technical standpoint. however, it may
be misleading to those unfamiliar with collodion collections and the process by which they are
made. The term “flow marks” and “varing thickness” imply a three dimensionality associated
with the collodion layer. the three-dimensional surface character of collodion plates observed
by the naked eye is primarily a result of the thicker varnish layer.
5.. To achieve the desired three-dimensional effect, the position of two camera-generated
stereo images must be laterally swapped. In production shops, stereo plates were often cut in
half and the positions swapped and mounted with gummed paper tape to a secondary glass
support to facilitate contact printing. This single procedure eliminated the need to trim
numerous prints before mounting.
6.. The secondary effect described by Brems is apparently more relevant to collodion negative
deterioration than the primary effect seen in the degradation of cellulose nitrate-based
negatives.
7.. The use of organic solvents, such as Kodak Film Cleaner (1,1,1 trichloroethane) on
collodion plates is not recommended. The varnish layer, as well as the underlying collodion
binder layer, are soluble in most organic solvents. Treatment with organic solvents may result
in loss of image.
REFERENCES
ANSI. 1986. American national standard for photography (processing): Processed films
plates, and papers—Filing enclosures and containers for storage.ANSI PHI.53-1986. New
York: American National Standards Institute.
Archer, F. S.1854. The collodion process on glass. 2d ed.London: Printed for the author.
Barger, M. S.1985. Characterization of deterioration of glass supported photographic images.
Printing of Transcript Summaries, Second International Symposium: The Stability and
Preservation of Photographic Images, Society of Photographic Scientists and Engineers,
Ottawa, Canada, August 25–28, 1985.
Barger, M. S., D. K.Smith, and W. B.White. 1989. Characterization of corrosion products on
old protective glass, especially daguerreotype cover glasses. Journal of Materials Science24:
1343–56.
Brems, K.A.H.1988. The archival quality of film bases. Journal of the Society of Motion
Pictures and Television Engineers (December):991–93.
Brill, Robert H.1978. The use of equilibrated silica gel for the protection of glass with
incipient crizzling. Journal of Glass Studies20: 100–118.
Coe, B., and M.Haworth-Booth. 1983. A guide to early photographic processes. London:
Victoria and Albert Museum.
Eastman Kodak Co. 1979. Preservation of photographs. Rochester, N.Y.: Eastman Kodak Co.
Eastman Kodak Co. 1985. Conservation of photographs. Rochester, N.Y.: Eastman Kodak
Co.
Feldman. L. H.1981. Discoloration of black-and-white photographic prints. Journal of
Applied Photographic Engineering7(1): 1–9.
Gill, A. T.1978. Photographic processes: A glossary and chart for recognition. Museums
Assocation Information sheet 21. London: Museums Assocation.
Gillet, M., C.Garnier, and F.Flieder. 1986. Glass plate negatives: Preservation and restoration.
Restaurator7(2):49–80.
Lavedrine, B., and C.Garnier. 1989. Analysis and restoration of negatives intensified with
mercuriclodide. In Topics in Photographic Preservation, Vol. 3Washington, D.C.:
Photographic Materials Specialty Group of the American Institute for Conservation of
Historic and Artistic Works.
Lea, M. C.1871. A manual of photography. 2d ed.Philadelphia: Printed for author.
Moser, F.1961. A study of glass surface deterioration by moisture. The Glass Industry42
(May):244–86.
Munson, D.1982. Duplication of glass negatives. Picturescope (Spring):19–23
Ostroff, E.1974. conserving and restoring photographic collections. Part 3.Museum News
(November) 42–45.
Ram, A. T., and J. L.McCrea. 1988. Stability of processed cellulose ester photographic films.
Journal of the Society of Motion Picture and Television Engineers June.
Reilly, J. M.1979. The albumen and salted paper book. Rochester, N.Y.: Light Impressions.
Reilly, J. M.1986. Care and identification of 19th-century photographic prints. (with C.
McCabe) Kodak Publication G-2S. Rochester, N.Y.: Eastman Kodak Co.
Rempel, S.1979. The care of black-and-white photographic collections: Identification of
processes. Canadian Conservation Institute Technical Bulletin 6. Ottawa: Canadian
Conservation Institute.
Rempel, S.1987. The care of photographs. New York: Nick Lyons Books.
Segal, V. M., I. E.Bolotov, L. V.Rabinovich, R. Ya.Liberman, and L.P.Zhukova. 1976.
Crystalline deposit on polished surfaces. Soviet Journal of Optical Technology. 43(10):607–
10.
Simpson, H. E.1958. Study of surface structure of glass as related to its durability. Journal of
the American Ceramic Society. 41(2):43–49.
Simpson, H. E.1959. Study of surface durability of container glasses. Journal of the American
Ceramic Society42(7):337–43.
Time Life Books1972. Cuting for photographsNew York: Time Life Books.
Towler, J.M.D.1879. The silver sunbeam, 9th ed.New York: E. and H. T.Anthony.
Weinstein, R. A., and L.Booth. 1977. Collection, use and care of historical photographs.
Nashville: Tenn.: American Association for State and Local History.
Wilkin, L. D., and B.London. 1979. The photograph collector's guide. Boston: New York
Graphic Society.
AUTHOR INFORMATION
CONSTANCE MCCABE received her MFA in 1982 at Rochester Institute of Technology in
the School of Photographic Arts and Sciences' Museum Practice Program and served
internships with the George Eastman House and the Image Permanence Institute. At the time
of writing this article, she was senior photograph conservator at the National Archives in
Washington, D.C. She is currently working as a photograph preservation consultant and is
president of Photo Preservation Services, Inc., a negative duplication service, Address: 409
Constitution Avenue, N.E. #4, Washington, D.C. 20002.
Section Index
Copyright © 1991 American Institute of Historic and Artistic Works
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