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OCR for page 33
4
Paper
The word paper comes from papyrus, a sheet made by pressing together very
thin strips of the Egyptian reed Cypenls papynls McGovern, 1978~. However,
papyrus sheets are not considered paper because the individual vegetable fibers are
not separated and then reformed. Paper, by its traditional definition, must be made
from natural fiber that has been macerated until each individual filament is a
separate unit, the fibers are dispersed in water, and by use of a sieve-like screen the
water is drained from the fiber, leaving a sheet of matted fiber on the surface of the
screen. When dried, this thin layer of intertwined fiber is paper ~Hunter, 1978~.
Modern paper manufacturing equipment employs this same principle in forming
the paper web.
RAW MATERIALS AND STRUCTURE
Cellulosic plant-derived fibers are the raw materials that make up the major
part of all papers. Natural plant fibers consist of crystalline filamentous cellulose
that is the structure of the skeleton of the fiber. Chemically, cellulose is a linear
polymer of beta-D-glucopyranose units linked by 1,4 glycosidic bonds. Isolated
samples are found to have molecular weight varying from perhaps 50,000 to more
than 1 million for a degree of polymerization of upwards of 7,000 and a length
exceeding 0.003 cm. Cellulose has a monoclinic crystal structure characterized by
a repeat distance of 1.03 rim t two anhydroglucose units) in the chain, with the
repeat units assuming a chair configuration Mark, 1983~. X-ray evidence indi-
cates that purified wood and cotton cellulose is about 70 percent crystalline.
Lateral hydrogen bonds stabilize the crystal against relative displacement of the
chains in response to imposed physical forces. Cellulose is a white substance that
is hydroscopic in nature, insoluble in most solvents, and resistant to the action of
most chemicals except strong acids. It is a stable organic polymer, and under
suitable storage conditions it can be preserved for centuries or millenia without
severe deterioration. Natural cellulosic fibers are structurally quite similar, and
33
OCR for page 34
34
PRESERVATION OF HISTORICAL RECORDS
the fibers of cereal straws, bagasse, kenaf, bamboo, esparto, hemp, jute, flax,
cotton, bark, and wood are used to manufacture paper. Wood pulp has proved to be
the most important source of papermaking fiber {Emerson, 1980a, 1980b).
Bleached chemical wood pulp and cotton fibers can be used to produce high-
quality, stable papers.
The wall structure of cotton fibers is similar to that of wood fibers; it is
relatively thin and grows free of lignin. The molecular weight of cotton cellulose
at a degree of polymerization of 8,000 is slightly higher than that in wood, and the
crystallites are slightly longer. The longer virgin fibers used in textiles are too
valuable to be economical for paper {Rollins, 1965J. However, the cotton ginning
operation leaves a fuzz of short fibers on the cotton seed, and these shorter hair
fibers, or [inters, together with rags and textile clippings, are the sources of cotton
fiber for special papers.
Kraft or sulfate pulp is the major wood pulp produced, and it is used for many
grades of paper. If white paper or high-brightness pulp is to be produced, lignin and
the hemicelluloses must be removed from the pulp fiber by bleaching. Multistage
bleaching with agents such as chlorine, chlorine dioxide, caustic extraction, and
peroxides is used to produce high-brightness pulp. Chemical wood pulps are clas-
sified according to the pulping process used e.g., soda pulp, sulfite pulp, and kraft
or sulfate pulp. These three chemical pulps in the fully bleached form are suitable
for producing archival papers.
The remaining classes of commercial pulps e.g., groundwood, semichemi-
cal, and thermomechanical are not suitable for use in archival papers because of
their lignin content. Unlike the highly stable crystalline cellulose, lignin is an
amorphous, complex, polydisperse polymer network of phenylpropane units with
a number of reactive functional groups that changes to a more highly colored form
as it ages. For this reason, papers made with lignin-containing fibers tend to
discolor with age {Sjostrom, 1981~.
Wood fibers are typically from 1.0 to 5.0 mm in length and from 25 to 50 ,um in
width and about 5.0 ,um thick. Because of their unique structure, wood fibers
exhibit a higher strength-to-weight ratio than any other structural material, with a
modulus of elasticity or Young's modulus of 3 x 105 kg/cm2 as compared with 2 x
106 kg/cm2 for steel. The number of fibers per gram will depend on their weight per
unit length. Individual fiber weights are in the range of about 1 x 10-6 to 3 x 10-6
g/cm {Corte, 1982J. Browning t1970) has calculated that there are from 1 to 10
million fibers in 1 g and that about 1,000 fibers placed side by side in one layer will
span 1 in., showing an average fiber width direction span of 25.4 ,um in the formed
web. In forming the paper web, fibers of various dimensions are arranged in an
interlocking network to form a sheet whose structure is determined by the spatial
distribution and orientation of the various fiber fractions.
Fibers in paper lie essentially in the plane of the sheet, giving paper a layered or
laminar structure but not discrete layers. This results from the thickening and
filtration that take place as the water is removed. In the drying stage of the web,
removal of the water permits the establishment of hydrogen bonds between the
fibers. Hydrogen bonds are now generally accepted as the cause of mechanical
coherence of paper {Corte, 1980~. Nissan { 1983) has pointed out that paper may be
treated as a continuum of hydrogen bonds, with the two parameters that deter-
mine the modulus of elasticity being the stretch force constants of the hydrogen
OCR for page 35
PAPER
35
bonds and the density of such bonds per unit area. He also observes that the
hydrogen-bond theory explains the mechanical behavior of paper in terms of inde-
pendently derived molecular and thermodynamic parameters. If variance is
assumed around the mean value of the hydrogen bond, the rupture energy of paper
can be related to the number of hydrogen bonds Nissan, 1983~.
Centuries of man's experience with paper have shown that the hydrogen
bonds established at the time of manufacture remain intact throughout the life of
the paper product, assuming normal storage and use conditions. The strength,
integrity, and concentration of the hydrogen bonds in the paper structure help
preserve the strength of paper under adverse storage conditions, such as oxidizing
atmospheres that degrade the cellulose polymer. On the other hand, if water is
reintroduced into the interfiber bond area, it may be absorbed by the hydroxyl
groups of cellulose that are associated with the hydrogen bonds of the paper struc-
ture. In this way, water can effect reversal of the interfiber bonds and greatly
weaken the paper. Although hydrogen bonds are re-established upon removal of
the water through drying, they may be displaced, causing cockling of the paper and
possible loss of strength. Using this reversible action of water, used paper can be
repuiped with water and wetting agents and recycled to form paper products using
reclaimed pulp. The properties of these pulps are generally lower in strength and
brightness than comparable virgin pulp. Contamination by plastics is also a major
problem. Reclaimed fibers are not recommended for archival papers.
Many types of nonfibrous raw materials are added to improve the physical,
optical, and electrical properties of the resulting paper Browning, 1970; Clark,
1978J. Polymeric binder materials are used to improve the cohesion of the individ-
ual fibers and increase the strength and stiffness of the paper. Bonding agents
include such materials as starch, modified starches, gelatin, polyvinyl alcohol,
methylcellulose, and latex or water emulsion materials such as polystyrene-buta-
diene, polyacrylates, and polyacrylamides. Inert inorganic materials known as
pigments or fillers are added to fill voids between the fibers and to smooth the
surface for printing tHagemeyer, 1984) . Fillers also improve the opacity and bright-
ness of the sheet, depending on the particle size, refractive index, and brightness of
these materials. Commonly used fillers include clays, talc, calcium carbonate,
titanium dioxide, aluminum oxides, and silicates. Pigments are used in varying
amounts, depending on the grade of paper, and may comprise 2 to 40 weight
percent of the final sheet.
Other additives include sizing agents that are used to reduce the penetration
of liquids such as offset printing solutions and fluid printing inks. Rosin, starches,
and synthetic resins are examples of sizing materials. The sizing agents may be
added as part of the paper raw material to produce internal sizing, or the dry sheet
may be passed through a size-press coaler that applies a surface size to the sheet.
Rosin is the most widely used sizing agent. The rosin is added to the paper
stock with one to three times as much aluminum sulfate, which precipitates the
rosin on the fibers as flocculated particles; after addition of the alum, the pH
should be 4.5 to 5.5. Sodium aluminate may also be used to precipitate the rosin
size, thus attaining slightly higher pH papers. Much attention has been focused on
the influence of acid conditions encountered during papermaking on the rate of
aging of paper. As a result, the production of paper under neutral to alkaline
conditions has gained in importance.
OCR for page 36
36
.~.
PRESER VATION OF HIS TOPICAL RECORDS
Photomicrographs of edge and surface of paper showing fiber structure. The
paperis a Nekoosa neutra]-pH cotton bond, sub. 20 (76 g/m2J, that meets
T A P P ~ , A S T M , a n ~ A N S · r e q u i r e m e n t s f 0 r p e r m a n e n c e .
OCR for page 37
PAPER
37
Internal sizing of papers under alkaline conditions {pH 7.0-9.0) is achieved
with synthetic sizes such as alkyl ketene dimer and alkenyl succinic anhydride.
These sizing agents are combined with calcium carbonate filler to provide a useful
pH control by a buffering action during aging of the paper. Recent decreases in the
cost of calcium carbonate filler and increases in the cost of virgin pulp have created
somewhat more favorable economics for alkaline pH paper, resulting in increased
commercial interest and production of this type of paper.
PHYSICAL PROPERTES
A sheet of paper has been defined as a foil with a fibrous fine structure. It is the
structure that determines the physical properties of the paper, and any change in
structure affects these properties. The properties required for various types of
paper, such as bond, writing, printing, book, envelope, and tablet, are developed
by the paper manufacturer through fiber selection and refining, type and amount
of additives, manufacturing process parameters, and conversion processes includ
. , .
ng surface coatings.
The behavior of the paper structure can be shown by typical stress-strain
curves for tension, compression, or shear {Setterholm and Gunderson, 1983~. In
the tensile test, when a piece of paper is subjected to a tensile load it stretches in
exact proportion to the applied load, and when the load is released it returns to its
original length only if the load does not exceed the elastic limit. If the applied load
exceeds the elastic limit of the sample and is released, the piece of paper will
contract but not to its original length. The permanent length increase is due to
inelastic response of some of the elements or of the fibers that are stretched or
straightened in the direction of the load. Under constant load above its elastic
limit, paper exhibits viscoelastic creep, and at some maximum value of stress the
paper undergoes tensile failure. Typically, elastic response will continue for about
one-fourth of the failing stress. In a review of paper behavior, Perkins {1983)
presents data to show that in a controlled environment paper will exhibit elastic
behavior under low loads of short duration, viscoelastic behavior under low loads
of long duration, and inelastic behavior as the level of stress increases. He points
out that microfailure could be the result of a variety of processes, including tensile
fracture of fibers, failure of fiber-to-fiber bonds, and development of slip planes
within the fiber cell walls. The inelastic response of paper is similar to other
materials such as reinforced fiber composites. In any event, tensile strength is the
force parallel to the plane of the sheet that is required to produce failure in a
specimen of specified width and length under specified conditions of loading
{Technical Association of the Pulp and Paper Industry iTAPPI] T404 and T494,
1984).
Stretch is the extension or strain resulting from the application of tensile load
under specified conditions {TAPPI T404 and T494~. The initial slope of the load-
elongation curve defines the modulus of elasticity or Young's modulus in the
machine or cross-machine direction. Stretch is greatest in the cross-machine
direction.
Tearing strength is the average force required to tear a single sheet of paper
under standardized conditions {TAPPI T414~. Fold endurance is the number of
folds a paper can withstand before failure {TAPPI T423 or T511). Brightness is the
OCR for page 38
38
PRESERVATION OF HISTORICAL RECORDS
reflectivity of paper or pulp for light at 457 rim {TAPPI T452~. Color is measured by
reflectivity according to TAPPI T442 and T524. Opacity relates to the ratio of the
diffuse reflectance of the sheet when backed by a black body to that when backed
by a white body {TAPPI T425~.
It is well understood that temperature has an effect on paper properties and
that moisture content has an even larger effect. Pulp and paper are hydroscopic and
can absorb water from or lose it to the surrounding atmosphere. As a result, paper
properties will change with changes in relative humidity; therefore, the control of
relative humidity in the environment for long-term storage of paper records is very
important. The influences of water content on the rate of degradation of cellulose
have been reported {Graminski et al., 1978) and show that the effect of tempera-
ture was less than that of moisture. A molecular layer of water on cellulose occurs
at about 5 percent moisture content, and the mechanical strength properties
decrease rapidly when the absorbed water exceeds 5 to 7 percent because of the
competition between the water molecules and the hydroxyls of cellulose for the
hydrogen bonds with other hydroxyls. In addition, Kadoya and Usuda {1984J
found that, at 80 percent relative humidity, the fracture mechanism under load
changed from bond breaking to fibers sliding out of the network. It is important to
carefully control both temperature and relative humidity in pulp and paper test
laboratories and to carefully condition test samples before testing See TAPPI
Standard T402-70) to obtain reproducible results.
PERNIANENCE FACTORS
Aging studies, by a number of investigators, on papers that have retained their
properties over very long periods of time, such as books that have survived for
centuries, show clearly the importance of composition in the keeping properties of
paper. Hudson's {1976) studies identify the quality of the fiber and the level of
acidity as key factors in paper permanence. He shows that there is a good correla-
tion between cold-water-extraction pH and resistance to heat-aging of paper.
Through raw material selection and pH control it is possible to make paper that
will store for centuries information of importance to civilizations, and this paper
permanence can be increased through the use of controlled storage conditions of
temperature and humidity consistent with requirements for use. The potential
value of cold storage for books and papers that are not in active use was shown by
the work of Hudson jl976) and Hudson and Edwards {1966) on books kept in
Antarctica from 1912 until 1959 compared Faith books from the same edition kept
in London. Those in the Antarctic were in essentially new condition, while those
stored in London showed extensive deterioration.
Nakagawa and Shafizadeh ~ 1984) showed that pure cellulose has a high degree
of thermal stability up to 300°C in an inert nitrogen atmosphere. They investi-
gated the rate of change in the molecular weight of cellulose versus time of aging in
air at 150°C and 190°C and found that the rate of change decreases with time of
aging. This result agrees with earlier findings that the rate of aging in paper under
accelerated aging conditions decreases with time. This indicates that the initial
rate of aging for paper under controlled storage conditions, as determined by the
rate of change in physical properties such as fold endurance, will decline as the
sample ages. Browning ~ 1970) reviewed the role of raw material selection and the
OCR for page 39
PAPER
39
value of paper is a major factor in developing and controlling paper permanence
and that low-pH papers age more rapidly than neutral to alkaline papers. They give
examples of ancient papers that have kept for centuries, many of which remain in
good condition today. Test results on these papers suggest that the permanence
exhibited is due to an alkaline to neutral pH value or an alkaline filler or both. The
OCR for page 40
PRESERVATION OF HISTORICAL RECORDS
r o ~ ~ Jay
~ ~ ~ ~ ~:~:
~ it: day., -
~ Y
._
~ ...
Effects of slow-working acidin booLpaper. Peter Waters, conservation
officer at the Library of Congress, demonstrates that a heftypuffmakes
confetti of dleteriorate~pages.
OCR for page 41
PAPER
41
benefit of an alkaline reserve is demonstrated by the keeping qualities of paper
contained in a book published in 1801. The paper was made by combining straw
pulp and groundwood pulp with chalk as a whitening agent. The paper is in good
condition in the personal library of I. d'A. Clark { 1978~. Barrow's { 1960) results on
old books showed that one book, published in Venice in the 17th century, that had
unusual keeping qualities contained an unusually high level of calcium carbonate
filler. This suggests that permanent papers can be produced using refined lignin-
free wood pulp that has an alkaline filler. Information based on the composition of
such well-preserved centuries-old paper samples has influenced favorably the
development of standards and specifications for the production of archival-quality
papers See section on Standards and Specifications later in this chapter).
Kelly ~ 1972) has shown that for a given type of paper it is possible to calculate
the rate of acid development caused by effects from such conditions as rosin-alum
size, contact with acid atmospheres tSO2, NOX), and oxidation; also shown is the
offsetting effect of an alkaline filler in the sheet. His calculations indicate that the
acid generated by the paper-based reactions is neutralized by the excess alkali
contained in the sheet. He reviews the possible mechanism for acid generation,
including the role of trace metals as oxidation catalysts. As a result, it is proposed
that archival paper be made with an alkaline reserve and be free of oxidation
catalysts. Both Williams {1979) and Browning t1969) find that the properties
required for archival-quality papers are well established. Papers meeting these
requirements can be produced using commercially available raw materials,
including fiber and filler, and processes that yield neutral alkaline pH in the final
sheet. Archival paper records printed on such a paper base will keep for centuries
under suitable storage conditions.
PRESERVATION
The problems of paper preservation associated with the low permanence of
acid-sized papers have led to extensive investigations of laboratory- and produc-
tion-scale processes for increasing permanence of existing paper records such as
maps, charts, documents, and books. Smith and Wilson I 1970) reviewed a number
of deacidification procedures, with particular emphasis on a nonaqueous process
developed by Smith. This process, involving the treatment of the paper with an
organic solvent solution of an alkali or alkaline-earth alkoxide such as magnesium
methoxide, has been developed to commercial-scale practice by Smith; the com-
mercial-scale process is described in U.S. Patents 3,676,055 and 3,676,182.
Williams and Kelly have reduced a method of deacidifying paper to practice
{U.S. Patent 3,969,549, 1976), and a commercial-scale facility is currently being
planned by the Library of Congress. The method involves exposing the paper to the
vapors of diethyl zinc followed by in situ hydrolysis of the zinc compound to a
mildly basic material. Barrow and Sproull jl959) proposed deacidification of
papers by soaking them in a solution of calcium hydroxide followed by a further
soak in a solution of either calcium or magnesium carbonate, which leaves cal-
cium carbonate in the paper. Although this method has been widely used by
conservators in preserving individual documents, maps, and prints, the wet paper
is very fragile and must be handled with extreme care until dry. This process is not
practical for large-scale conservation because of the time required and the need for
highly trained personnel.
OCR for page 42
42
PRESER VATION OF HIS TOPICAL RECORDS
The use of magnesium bicarbonate solutions for paper deacidification has
been investigated by Wilson and co-workers {1981) at the National Archives. A
recent dry process for deacidification, reduced to practice by Kundiot {as described
in U.S. Patent 4,522,843), uses an airborne technique to deposit fine particles of
MgCO3 on the paper surface. The effectiveness of the process is not known. This
development is in accordance with the work of other investigators reported here
regarding the effectiveness of an alkaline reserve, which may be added at any time,
in extending the useful life of paper.
The results from a number of laboratories over many years show clearly that
deacidification procedures are effective in reducing the rate of aging of paper that
was not produced according to archival standards. The type of deacidification
procedure selected would depend on the type of paper or population requiring the
treatment. It should be noted that deacidification does not add physical strength to
papers that are treated. All of the currently available deacidification processes may
damage certain documents through heat, pH changes, or solvent effects on some
inks. This makes it necessary to examine individual documents to exclude those
subject to damage by the process used. Because individual document screening
would be very costly, mass deacidification is not recommended for the unbound
Archives collection.
A review of the patent literature in the United States and Great Britain by Baer
and Hanson { 1983J shows a high level of activity in paper deacidification methods
and materials, with about 20 patents issued.
In addition to these chemical preservation processes, plastic materials for
paper preservation and restoration have been extensively investigated and used.
Wilson and Parks { 1983) reviewed and described a number of reports of investiga-
tions and actual use of lamination and encapsulation. Their review includes dis-
cussion of the importance of mechanical protection with better enclosures and
alkaline folders. When paper is encapsulated or laminated, even very old and very
fragile paper can be safely handled, thereby prolonging its useful life. The develop-
ment and use of a number of preservation methods and materials was reviewed by
Roberson {1981~.
STANDARDS AND SPECIFICATIONS
Kelly and Weberg { 1981 ) reviewed paper specifications developed by a number
of organizations for pe~'anent or archival papers, including the Library of Con-
gress, the American National Standards Institute {ANSI), the American Society for
Testing and Materials {ASTM), the National Bureau of Standards {NBSJ, the Soci-
ety of American Archivists, and Barrow Laboratories. The specifications listed for
paper permanence include a pH of 7.5 to 10.3, at least a 2 percent calcium carbo-
nate reserve in the paper, and the absence of lignin or groundwood pulp. It is
estimated that papers meeting the specification should have a probable life of 500
to 1,000 years under good storage conditions. Work on the development of specifi-
cations at the National Bureau of Standards, including literature on the stability of
paper, was reviewed by Wilson (1974~. A general review of the principles involved
in alkaline sizing, which is specified for permanent paper, was presented by Tosh
{1981~. Sizing agents that operate without alum, such as alkyl ketene dimers or
anhydrides, are recommended.
OCR for page 43
PAPER
43
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_~
. ~ `'
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:'~ ,
, i .,, '.:i ~. :,
< ~ it, hi
'A < ~-myth
~ "A 'I ~
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Hi,, - : ,, i,,
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Document encapsulation. Paper that is too fragile forhnndling can be
protected between sheets of transparentpJasticfi~m.
OCR for page 44
44
PRESER VATION OF HIS TOPICAL RECORDS
Specifications for papers for permanent records have been published by ANSI
and ASTM. Test methods applied to paper have been published by the Technical
Association of the Pulp and Paper Industry {TAPPI). Each TAPPI standard for
permanent paper designates three levels of permanence: Type I, Maximum Per-
manence, pH 7.5-9.5; Type II, High Permanence, pH 6.5-8.5; and Type III,
Medium Permanence, pH 5.5 minimum. In addition, a 2 percent calcium or
magnesium carbonate filler level is specified for Type I papers. The ANSI and
ASTM standards are designated D3290-76, Bond and Ledger Paper for Permanent
Records; D3208-76, Manifold Papers for Permanent Records; D3301-74, File Fold-
ers for Storage of Permanent Records; D3458-75, Copies From Office Copying
Machines for Permanent Records; and Z39.48-1984, Permanence of Paper for
Printed Library Materials.
For the creation of paper records meeting archival quality standards, perma-
nent or archival paper should be used in combination with permanent or archival-
quality image-forming materials. Printing inks for printing presses and toners for
copying machines are a combination of pigments or colorants with a resin to bind
the pigment to the paper surface. A wide selection of both types of raw materials is
available to the ink and toner manufacturer, including materials of proved long-
term stability such as carbon black and colored stable inorganic pigments and
stable types of resin such as polyesters, polyamides, acrylics, and phenolics. Not
all inks and toners are designed for long-term stability; therefore, archival require-
ments should be applied in the selection of these materials for the creation of
archival-quality records. In addition, both the printing process and the copying
process should be operated under conditions that are optimum for promoting a
strong bond between the ink or toner and the paper surface. If these materials are
used in well-adjusted processes in combination with archival-quality paper
{ASTM D3458-75), the resulting paper record will keep under good storage condi-
tions for many centuries. A useful reference for guidance in selection of archival-
quality inks and toners and the xerographic process is the Printing Ink Manual
{1979~; see also Diamond il984) and Parks and Wilson {1974~.
ADVANTAGES, DISADVANTAGES, AND CONCLUSIONS
Advantages
The advantages of paper as an archival material are these:
1. The permanence of paper generally demonstrated through many centuries of
storage in collections throughout the world is an advantage for archival use.
2. The ease of producing copies of paper documents as a result of the worldwide
proliferation of copiers and duplicators in offices, libraries, airports, hotels, etc., is
an advantage for paper-based records. The copying process has no discernable
detrimental effect on the original.
3. Printers or "intelligent" copiers that produce paper copies directly from
computer-based records are an advantage in computer-based record systems.
These copiers can print a variety of information using computer-generated for-
mats at any location using satellite or telephone-line transmission.
4. The ready availability of neutral pH paper at regular commercial prices for
OCR for page 45
PAPER
45
use in generating archival-quality papers is an advantage today that did not exist a
few years ago.
Disadvantages
Paper's disadvantages are as follows:
1. Papers that are acid-sized show degradation during storage, and deacidifica-
tion may be needed to extend their useful storage life.
2. Many of the early copier and duplicator processes developed fragile or unsta-
ble copies that do not have longevity. In some cases the images were composed of
dyes that fade with time.
3. Paper-based records are bulky and involve manual operations.
Conclusions
The following conclusions regarding paper are drawn:
1. Experience with use and storage of paper records over many years has demon-
strated the centuries-long permanence of paper produced with near-neutral pH
made from bleached pulps and with an alkaline reserve.
2. Images formed on permanent paper with inks from printing presses or toners
from photocopying machines that use permanent-type materials such as carbon
black pigment and inert resin binders {e.g., polyester, silicone, polystyrene, and
epoxy) will remain legible for hundreds or thousands of years if protected by
suitable storage conditions.
3. The permanence of all papers can be extended through the use of proper
environmental conditions such as low temperatures, humidity control, and dark
storage.
4. Paper produced with an internal acidity below 5.5 pH and without an alka-
line reserve will have a lower degree of permanence, but increased permanence
can be achieved with treatment by laboratory or commercial deacidification
methods and the introduction of an alkaline reserve at any time during the paper's
useful life. Remedial actions include {aJ treatment by an alkalization process, such
as deposition of magnesium bicarbonate, when the original documents must be
preserved and {b) copying onto permanent paper with permanent toners to provide
long-term stability when the intrinsic value of a document is not important. This
procedure is particularly recommended when only part of a set or random sheets of
documents are to be preserved.
5. Papers that are damaged physically or that have become weak from aging
effects may be safely protected through encapsulation using acid-free alkaline-
reserve permanent papers or inert materials such as Mylar polyester film.
6. Under suitable storage conditions, the rate of aging decreases with time.
Paper that is shown by tests to be aging slowly will change to a lower aging rate if
stored under proper environmental conditions.
7. Inactive paper records may be safely stored at reduced temperature, includ-
ing below-freezing cold storage conditions, to extend their useful life.
OCR for page 46
46
PRESERVATION OF HISTORICAL RECORDS
REFERENCES
Baer, N. S., and K. Hanson. 1983. Survey of Patent Literature Pertaining to Deacidification of
Archives and Library Materials. New York: New York University Conservation Center of the
Institute of Fine Arts.
Barrow, W. J.1960. The Manufacture and Testing of Durable Book Papers, R. W. Church, ed. Publica-
tion 13. Richmond, Virginia: Virginia State Library.
Barrow, W. J., and R. C. Sproull. 1959. Permanence in book papers. Science, 129:1075-1084.
Browning, B. L. 1969. Analysis of Paper. New York: Marcel Dekker.
Browning, B. L. 1970. The nature of paper. Libr. Q., 40(1):18-38.
Browning, B. L., and W. A. Wink. 1968. Studies on the permanence and durability of paper. Tech.
Assoc. Pulp Pap. Ind. J., 5114~:156-163.
Cardwell, R. D., and P. Luner. 1978. Thermogravimetric analysis of pulp; kinetic treatment of
dynamic pyrolysis of papermaking pulps. Tech. Assoc. Pulp Pap. Ind. J., 61(8):81-84.
Clark, J. d'A.1978. Filling and bonding materials. Chapter 311pp. 664-678) in Pulp Technology and
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~;~
Film storage facilityin Granite Mountain records vault of the Genealogical
Society of Utah. Control of storage conditions is vital to ensure
permanence of stored records.
Representative terms from entire chapter:
hydrogen bonds
