Alkaline Paper Advocate

Volume 1, Number 1
Mar 1995

Letters to the Editor

The following letter from a preservation administrator at a university library came in January. Like many other university librarians, she is concerned about the permanence of the papers used for Ph.D. dissertations and master's theses, which are often retained indefinitely by the library of the issuing institution.

To the Editor:

... I talked to the dean of our graduate school the other day about appropriate dissertation/thesis paper. He wanted to know whether it was time once again to revise our specifications. When I talked about how specs might reflect the current NISO standard he said, "None of the paper is marked to indicate that it's alkaline, and/or meets the ANSI standard. I can't work with a statement that cites requirements which the student cannot verify from paper packaging."

I suggested that all we need to do is ensure that the University book store continues to carry appropriate options. He said, "People call me from all over the U.S.--they're getting a degree here but working elsewhere. They need to buy locally. The ANSI statement is not helpful in this case."

He's right. How can we promote an idea if the idea isn't marketed by product manufacturers? I told the dean I'd try to find out why paper packaging isn't marked. Do you know?

Jan Merrill-Oldham
University of Connecticut

[Note: Readers may recall Helmut Bansa's explanation of the German paper permanence standard, in the July issue, on p. 14. He did his best as author to make it clear, and I did my best as editor, but we were not entirely successful, as the following two letters will attest. We (Dr. Wilken, Dr. Bansa and I) all hope the material that follows will give a better explanation of how it works. Following Dr. Bansa's letter is an authorized English translation of three key sections of the standard: 3.1, "Minimum requirements"; 3.2, "Residual properties"; and 5, "Determinaton of life expectancy factor." These excerpts are reproduced by permission of DIN, Deutsches Institut für Normung e.B. The definitive version for the implementation of this standard is the edition bearing the most recent date of issue, obtainable from Beuth Verlag GmbH, Burggrafenstraße 6, D-10787 Berlin (fax 49 30 2601-231). This edition of DIN 6738 is the one of April 1992. In the U.S., it can also be purchased from ANSI, American National Standards Institute, 11 West 42nd St., 13th Floor, New York, NY 10036 (212/642-4900).]

To the Editor:

On going through the July issue of the Alkaline Paper Advocate, we found an article by Dr. Bansa which is entitled "Understanding the German Paper Standard DIN 6738." Since it appears that there might be some misunderstanding, we should like to clarify the following points:

DIN 6738 is based on the well-founded assumption that the aging rate of paper is not constant: it is high at the beginning and slows down with increasing age. In the case of both naturally and accelerated aged papers, the usability limits cannot be exactly defined, because the relevant paper properties approach this limit asymptotically. DIN 6738 defines the usability limit via minimum properties (MP) in terms of the following paper parameters:

tensile strength, CD mp=5 N
stretch at break, MD mp=0.5%
tearing resistance, MD mp=50 mN

A tensile tester and an Elmendorf device are required for testing. That makes two test devices instead of three as has often been wrongly claimed.

The author's statement that the determination of lifespan classes is based on the minimum properties of paper is untrue. Rather, the lifespan classes are defined via the aging rate of paper which is measured during accelerated aging. The eminent practicability of the standard and the reliability of classification are achieved with a special method of determining the aging rate.

To start with, the value of the original property (OP) is determined. Afterwards, the value of this property is re-determined after 6, 12 or 24 days of accelerated aging (RP=residual property). The two points thus obtained may be connected by a straight line which linearly approximates the natural aging rate. (See figure.)

DIN 6738 even goes one step further: the aging rate is standardized in relation to the minimum requirements by means of the lifespan factors fL. This enables the aging characteristics of totally different papers to be immediately compared. For completeness, the definition of the lifespan factor is given below:

          RP - MR
    fL =  -------
          OP - MR


    OP = original property
    RP = retained property
    MR = minimum requirement

A crucial aspect in this context is that the linear approximation of the actually nonlinear aging rate of paper yields an extremely cautious estimate of the life expectancy of paper. The probability of obtaining a false--i.e., an all-too-high--life expectancy is thus negligibly small.

R. Wilken
Papiertechnische Stiftung

Dr. Bansa replies:

The factual content of Dr. Wilken's letter is--with one exception: see below--exactly the same as the factual content of my text in the Alkaline Paper Advocate, July 1994, p. 14. The only difference is: my text uses clear words, understandable by anybody, while Dr. Wilken, as well as the standard itself, uses a formula with newly introduced ideas that are hard to understand, i.e., hard to combine mentally with practical and realistic concepts. The obscurity of the German standard was the very reason for my text in the Alkaline Paper Advocate: American friends had asked me to translate it into clarity.

The misunderstanding between Dr. Wilken and me might have linguistic reasons. My text sent to the Alkaline Paper Advocate was as follows: Compute in what amount the numbers checked after 24 days of aging have approached to 5 N (tensile), to 0.5% (stretch at break) and 50 mN (tearing resistance). The Alkaline Paper Advocate changed this to: "Calculate how much strength has been retained after aging, based not on the paper's actual original strength, but on the standard's 'minimum requirements': 5N (tensile), 0.5% (stretch at break) and 50 mN (tearing resistance)."

Helmut Bansa
Bayerische Staatsbibliothek

[The three sections of the German paper permanence standard that are most relevant to the above discussion are reproduced on the next page, with permission. They define the minimum requirements, specify the residual properties, and describe how to calculate the life expectancy factor.]

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