Acid-free paper

Acid-free paper

Acid-free paper is paper that has a neutral or basic pH (7 or slightly greater). It addresses the problem of preserving documents for long periods.


Paper made from wood-based pulp that has not had its lignin removed goes yellow and deteriorates over time. [Teygeler, R. (2004). Preserving paper: Recent advances. In J. Feather. (Ed.)," Managing preservation for libraries and archives: Current practice and future development." 90. Burlington: Ashgate. ISBN 0754607054 ] When exposed to light and/or heat, the molecules in the acidic paper will break down even faster. [ Arnold, B.R. (2002). ASTM’s Paper Aging Research Program. Retrieved November 4, 2007, from] It was only in the 1930s that the effects of wood-pulp paper became known, when William Barrow (a librarian) published a report about the deterioration of acidic paper in the libraries. [Cedzova, M. et al. (2006). Patents for Paper Deacidification. "Restaurator: International Journal for the Preservation of Library and Archival Material," 27, 35.] For fear of the gradual disintegration of written materials, measures have been taken to improve the quality of paper.

During production, acid-free paper may be treated with a mild base (usually calcium or magnesium bicarbonate) to neutralize the natural acids occurring in wood pulp, and it may also be buffered to prevent the formation of additional acids (as may develop from the application of sizing).

The bicarbonate is added in excess, to supply the paper with an alkaline reserve to provide protection from further attack by acids remaining in the paper or supplied by the environment (e.g. atmospheric sulfur dioxide). [] The bicarbonate during drying loses carbon dioxide and water and is converted to calcium carbonate or magnesium carbonate. In order for paper to last at least 100 years it must have an alkaline reserve of 2% or more. [Teygeler, R. (2004). Preserving paper: Recent advances. In J. Feather. (Ed.), "Managing preservation for libraries and archives: Current practice and future development." 89. Burlington: Ashgate. ISBN 0754607054 ]

Today, much of the commercially produced paper is acid-free, [Dahlo, R. (2000). The Rationale of permanent Paper. In W. Manning & V. Kremp (Eds.), "IFLA Publications 91: A Reader in preservation and conservation." 59. Munchen: K. G. Saur. ISBN 3598218176. ] but this is largely the result of a shift from china clay to (cheaper) chalk as the main filler material in the pulp: chalk reacts with acids, and therefore requires the pulp to be chemically neutral or alkaline. The sizing additives mixed into the pulp and/or applied to the surface of the paper must also be acid-free.

Alkaline paper has a life expectancy of over 1,000 years for the best paper and 500 years for average grades. [ASTM D 3290-00, "Standard Specification for Bond and Ledger Papers for Permanent Records", section and Appendix X1] The making of alkaline paper has several other advantages in addition to the preservation benefits afforded to the publications and documents printed on it. Because there are fewer corrosive chemicals used in making alkaline paper, the process is much easier on the machinery, reducing downtime and maintenance, and extending the machinery's useful life. The process is also significantly more environmentally friendly. Waste water and byproducts of the papermaking process can be recycled; energy can be saved in the drying and refining process; and alkaline paper can be more easily recycled. [Lundeen, G.W. (1983) Preservation of paper based materials: Present and future research and developments in the paper industry. In K.L. Henderson and W.T. Henderson (eds) "Conserving and preserving library materials (Papers presented at the Allerton Park Institute November 15-18, 1981)": 73-88. Retrieved from]

tandards for Acid-free paper

The company Hercules Incorporated developed the first alkaline size in the 1950s that made acid-free paper possible [] . Despite the advances in paper making and the identification of and concern around the brittle book problem, it took decades before the adoption of ANSI NISO Standard Z39.48-1984 - "Permanence of Paper for Publications and Documents in Libraries" in 1984. This voluntary standard covered pH value, tear resistance, alkaline reserve, and lignin thresholds for paper to last thousands of years and was developed to encourage the use of acid-free paper in library materials [] . The development of the initial standard was a result of the work of the Council on Library Resources, which effectively lobbied ANSI to adopt the guidelines. [Ward Brown, J. (May 1985). The Once and Future Book: The Preservation Crisis. Wilson Library Bulletin, 59, 591-6.]

In 1986, Standards Committee II of NISO was established to expand Z39.48-1984 to develop standards for coated paper, and was again called upon in 1988 to review and revise the standards for uncoated paper.

There are various standards for "acid-free" paper, with differing requirements. In some quarters, paper having a pH between 6 and 7 is often also considered acid-free. Acid-free (alkaline) paper that additionally is "uncoated" and meets certain "standards for folding and tearing" is authorised by the American National Standards Institute (ANSI) to carry the following notice: "The paper used in this publication meets the minimum requirements of the American National Standards Institute for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48-1992."

The objective of ANSI Z39.48-1992 "is to establish criteria for coated and uncoated paper to last several hundred years" [] under optimal conditions in libraries and archives. The desired outcome of the standard is to reduce future preservation problems.

The scope of the standard is to cover publications and documents bought and maintained by libraries and archives. Such works include scholarly journals, periodicals, monographs, government documents, original documents, and significant works in fiction and non-fiction.

The sign of ANSI approved alkaline paper is the "circled infinity symbol". [The Chicago Manual of Style Online §1.35;] There is a unicode Permanent Paper sign (♾) at codepoint 267E.

Archival Paper

Archival paper is an especially permanent, durable acid-free paper. Archival paper is meant to be used for publications of high legal, historical, or significant value. In the USA, such paper must also be approved in accordance with the ANSI standards. [] The international standard for "permanent" paper is ISO 9706 and for "archival" paper, the standard is ISO 11108. [Dahlo, R. (2000). The Rationale of permanent Paper. In W. Manning & V. Kremp (Eds.), "IFLA Publications 91: A Reader in preservation and conservation." 58. Munchen: K. G. Saur. ISBN 3598218176. ]


Another form of "archival paper" is being made from recycled plastic in the form of Durabook. This is a patented material and process developed by Melcher Media, a New York publisher. [Donadio, R. (July 2006). Saving the Planet, One Book at a Time. New York Times. ] Plastic paper does not have lignin [Hilts, P. (October 2000) Splish, splash, take a book to the bath. Publishers Weekly, 247, 39.] to cause acid problems or cellulose fibers that can break from folding. It also will not be damaged if soaked in water and, if the book gets dirty, can be washed. The only issues to consider are what type of plastic is being recycled and if those plastics will break down in the future.


External links

* [ Acid-Free Paper]
* ASTM D1994-07 Standard Test Method for Determination of Acid Numbers of Hot-Melt Adhesives

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