Abbey Publications
Abbey Publications
Selections from North American Permanent Papers
Ellen McCrady <abbeypub@flash.net>
1998

The Nature of Permanence

by Ellen McCrady

"Permanence," like any other word, is defined by the way people use it, and may have different meanings in different contexts. Here, for the sake of clarity, we will use the definition found in the ANSI/NISO standard, Z39.48-1992: "The ability of paper to last at least several hundred years without significant deterioration under normal use and storage conditions in libraries and archives."

Any discussion of permanence involves more than a definition, though. Some of the most closely related topics are briefly discussed below.

Durability and Its Relation to Permanence

The best definitions of permanence and durability, in my opinion, were those written by Bertie L. Browning. One is from the introduction to the Institute of Paper Chemistry's 1964 Permanence bibliography (Bibliographic series, No. 213), and two are from his 1960 book, The Nature of Paper:

In historical and colloquial usage, the terms permanent and durable have been used synonymously, but of course some precision is lost in doing so.

Chemical and Physical Aspects of Paper Deterioration

Chemical deterioration is a result of reactions that may be set off by some form of energy (heat, light, gamma radiation) or by contact with acidic or oxidizing gases, especially under conditions of high humidity; these reactions may be augmented by unstable components in the paper itself. Large fluctuations of relative humidity or temperature will also speed up these reactions (at least under conditions of artificial aging).

Chemical reactions that deteriorate paper may also be caused by the presence of bacteria and fungi, which secrete enzymes; by oxygen or pollutant gases in the air; light, which induces slow oxidation; fire, which causes rapid oxidation; gamma rays; fumigation with certain insecticides and fungicides; and the presence of metals, lignin, acids and other substances in the paper. Some of these agents increase the effect of other agents: for example, high humidity accelerates deterioration from pollutant gases.

The effects vary, because not all deterioration reflects the same chemical or physical change in the material. Agents of deterioration often discolor and weaken the paper at the same time, but these effects may occur independently. Other less obvious changes may take place only after a delay, such as an increased vulnerability to the effects of heat following exposure to light.1

There is some debate today about whether resistance to yellowing should be a specification in a permanence standard. Artists and art owners think resistance to yellowing is important both for art papers and for books of collected prints, which may be disbound and framed separately; but for other uses, most people think strength is more relevant. Librarians and archivists, who are custodians of most of our really old paper, want both strength and brightness to be retained over time. They want paper to remain strong so that it can be used, and to resist yellowing so that it will be easier to photocopy or microfilm, and so that it will not darken while it is on exhibit.

Some people question whether it is necessary to consider strength in a permanence standard, since paper used for books and documents does not have to be nearly as strong as paper used for packaging. They do not realize that the strength of paper declines as it ages, and that it must be strong enough initially to give it a reasonable lifetime. Both strength and chemical stability increase the lifespan of paper.

Accelerated vs. Natural Aging

Paper chemists may age sample sheets in an oven, performing strength or other tests before and after aging, to evaluate their permanence. Tests measure certain characteristics that might be expected to change during natural aging: tear resistance, fold endurance, and so on.

If accelerated aging is intended to mimic natural aging, what is "natural aging"? Is it different for books, active records, art on paper, and private papers? What is a typical environment, and what is a typical degree of physical stress? There is little research on these questions. No single accelerated aging method will mimic all sets of natural aging conditions for all kinds of paper, but the conditions chosen should be as realistic and explicit as possible.

There are many examples of old paper, going back a thousand years or more, in museums and rare book collections; there are also millions of books printed on paper since the fifteenth century in libraries. All that paper was aged naturally. The examples that have come down to us were well made, while the ones that were poorly made have not. We do not know the conditions under which it was aged, but we can analyze the fiber and other components of the paper, evaluate its condition, note its age, and learn from paper historians how it was made.

Natural aging has also been studied in a more controlled way by the National Bureau of Standards, the National Testing Institute in Sweden, and a few researchers elsewhere. Paper is selected, tested, put away, and taken out at widely spaced intervals to retest. Sometimes the gases given off as the paper ages are identified, and some of the chemical changes in aging are described. Our understanding of natural aging continues to grow, but there is still much to learn.

Methods of Accelerated Aging

Accelerated aging in an oven was introduced to this country in the 1920s. Then fifteen or twenty years ago, moisture as well as heat began to be used in the aging oven, so as not to inhibit the reactions that involve water. Light or pollutant gases have also been used to age paper. The rate of degradation doubles with every 5°C (10°F) increase in temperature, approximately, but it is higher for poorer quality papers.2

The choice of aging temperature helps determine the changes that will be induced, and different changes are induced in different materials. A useful example of the effect of temperature is the egg: If you age it at 100°C, you get a hard-boiled egg; at the body temperature of a brooding hen, you get a baby chick; at room temperature, a rotten egg.

If old leatherbound books are aged at the high temperatures used for paper, the covers will shrink and turn dark and hard, which is not a normal effect of aging, so light or pollutant gases are used instead.

The Impossibility of Determining Just How Long a Given Piece of Paper Will Last

The everyday use of the term "permanent," as in "permanent wave" or "permanent address," does not imply that the thing described will last forever. It is the same with paper. Even paper that meets permanence standards may not last the expected 300 years, if it was made using a new chemical compound or procedure that has an unexpectedly harmful effect, or if it is handled and stored carelessly by the owner.

Although papermaking methods are changing rapidly and our understanding of the effect of storage conditions changes too, we are not likely to see any Big Surprises like the unexpected effect of chlorine bleaching powder after 1815 (which caused books to crumble before they could be sold), or of the disastrous combination of wood pulp with acidic sizing starting around 1870, because we have much better analytic methods and greater sophistication now.

Still, we have a lot to learn. Only fifteen or twenty years ago, ozone as a city pollutant was not thought to harm paper; now we know better. In Europe, optical brighteners are suspected of shortening paper's life; in this country, they are not seen as a threat to permanence. Because of all these considerations, we have to be humble and tentative about predicting how long a paper will last.

References

1. R.L. Feller, Sang B. Lee, and Mary Curran. "Three Fundamental Aspects of Cellulose Deterioration." Art & Archaeology Technical Abstracts, v. 22 #1, 279-357, 1985. p. 280.

2. David Erhardt, "Relationship of Reaction Rates to Temperature." Abbey Newsletter 13 (3), June 1989, p. 38-39.

North American Permanent Papers


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URL: http://cool.conservation-us.org/byorg/abbey/napp/perman.html
Timestamp: Sunday, 03-Mar-2013 21:43:07 PST
Retrieved: Sunday, 19-Nov-2017 23:56:42 GMT