Preservation of Knowledge, Part 1: Paper and Microfilm

In his wonderful, award-winning book Double Fold, Nicholson Baker makes a plea for preservation of printed materials, particularly newspapers.¹ He reports on the constant destruction of printed materials that have been preserved on microfilm, the latter presumably being more resilient to the passage of time than paper itself. Historically, paper was made from plants with long fibers (such as linen, cotton, and esparto), yielding a high-quality and long-lasting product. Some of the best linen paper, made in Japan, can survive for centuries. In a similar fashion, cotton-based paper is also of very high quality and long lasting. With the ever-increasing popularity of the printed word, new and more efficient ways of manufacturing paper were sought, and at approximately the mid-1800s it was discovered that wood pulp could be used for this purpose.² The Swedish were the first to use wood pulp for paper on an industrial basis.

Plants and trees, the main source of pulp for papermaking, also contain important polymers called lignins. These serve a function in the transport of water and in giving plants their structural strength. Here is an analogy: lignins are to plants as concrete is to a brick wall. If we grind a tree, the resulting pulp will contain lignin and fibers. To make stiff and strong paper (such as that found in supermarket bags), one needs a lot of lignins. The problem is, with time, lignins deteriorate and give off acids (particularly carboxylic ones). These acids cause paper to turn yellow (this is no problem with brown paper bags and other dark products with a short life). Exposure to light hastens this process, as does exposure to ambient air (comic book collectors tend to keep them in plastic bags). The byproducts of lignin deterioration damage cellulose, and the paper becomes brittle. That is why old newspapers are yellow-to-brown and tend to break off at creases.

One way to remove lignins is bleaching. Once the pulp has been extracted, it can be treated with a mild base (usually calcium or magnesium bicarbonate) to neutralize the naturally occurring acids. Additional base may be added to prevent acidity brought on by the process of “sizing.” Sizing generally involves the application of an acidic polymer to the surface of the paper that will basically prevent ink from spreading too much in the paper fibers (paper for color laser printing is heavily sized, making it is difficult to write on with a fountain pen, as the ink will not be absorbed and takes a long time to dry). Extraction and neutralizing of lignins make paper white (brown paper bags may contain up to 55% of unbleached pulp).

The process of bleaching builds into paper the so-called alkaline reserve. For paper to last at least 100 years, its alkaline reserve needs to be approximately 2%. Alkaline paper (called acid-free) can survive anywhere from 500 to 1000 years depending on its quality. Alkaline paper has innumerable advantages vs traditional acid paper including less wear on the machinery that produces it, papermaking by-products that are recyclable, less energy needed to dry it, and the paper itself being easier to recycle. In the paradoxic sense, as we add more recycled paper into new, we are increasing the content of postconsumer fibers and, again, introducing lignins and acidity. For completeness' sake, I would like to note that the absolute whiteness of the paper we commonly use cannot be achieved solely by bleaching. Initially, the pulp is thermo-treated (basically cooked), and whatever lignin is left behind from this process is then removed by bleaching. Bleaching initially involved the use of chlorine, but because of environmental concerns, other chemicals are now used. Thus, the first step in preservation of printed materials is improvement of the quality of paper.

As early as 1930, librarian William J. Barrow noted the deterioration of paper publications. He wrote several seminal articles on this topic from the 1940s to the 1960s and headed an important laboratory concerned with investigations regarding the quality of paper. Barrow's initial observations went basically unheard until the Council on Library Resources and the American Library Association granted him monies to pursue his investigations. In 1988, the National Endowment for the Humanities began the Brittle Books Program, which involved the microfilming of 3 million decaying books. The program also includes the deacidification of books that are still in good condition (because this is an aggressive process, it will actually damage those books that are decaying).

Microfilming, as evidenced by Mr. Baker's book, is highly controversial. Microfilm can last for approximately 500 years (less than high-quality paper), but it needs to be stored in proper conditions and viewed with special machines. Unfortunately, the quality of the material archived on microfilm is highly variable and many times is unreadable because sufficient care was not taken to optimally photograph the original publications. In 1984, the National Information Standards Organization (www.niso.org) proposed voluntary standards for paper manufacturing that included pH value (the pH of alkaline paper is 6.0–7.0), tear resistance, alkaline reserve, and lignin concentration. If followed, paper complying with these suggestions may last thousands of years. In 1994, the International Standardization Organization (www.iso.org) proposed international equivalent standards. Furthermore, both organizations suggest that publications of special significance be printed on archival-grade paper. The highest quality of this type of paper is called museum grade and is cotton based.

In 1987, the National Library of Medicine (NLM) created the Permanent Paper Task Force.³ This institution encourages the use of permanent paper that meets the criteria outlined in the Permanence of Paper for Publications and Documents in Libraries and Archives Act; all journals must be printed on acid-free paper and are identified as such in PubMed. Our printer, Cadmus, uses acid-free paper for the cover and contents of the American Journal of Neuroradiology (AJNR) and meets the requirements of the American National Standards Institute (www.ansi.org). The mill that produces our paper uses environmentally friendly chlorine-free bleaching.

So, although the issue of paper preservation has been at least partially solved, the problem regarding the amount of space required to store scientific journals has not. Of course, archiving on microfilm and microfiche has not proved to be as easy or reliable as initially thought. The NLM has a section dedicated to preservation and collection management that deals with these issues. Storage requires controlled temperature, humidity, light, and shelving; transportation is delicate and tricky, and viewing exposes film to significant physical stress that contributes to its deterioration. Microfilm is a cellulose acetate-based product that is very sensitive to physical trauma. Most university libraries own equipment that will allow one to print, e-mail, save images to USB devices, or burn them on CD or DVD. Loading the film tapes into these machines can be risky, and specific instructions need to be followed. Digitization of microfilm is being done but requires scanners capable of resolutions close to 10,000 dots per inch.

The one thing microfilm has clearly achieved is space savings. Storage requirements are reduced by nearly 95%. It also prevents further deterioration of original manuscripts by avoiding repeated handling. Color microfilm is extremely expensive; thus, most archives are only in black and white. Why the NLM chose microfilm to archive its material has been addressed in many articles and books. The development of microfilm during the First World War was related to espionage activities. Before becoming the NLM, this repository was called the Army Medical Library, and it was not until the mid-1950s that the Department of Defense transferred it to the Public Health Service. I doubt many neuroradiologists have consulted the microfiche carriage in our local library lately, as most biomedical data are now stored electronically. Next issue, I will continue this Perspectives with a brief account of digital storage activities as they relate to the sciences and to AJNR.

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