The Abbey Newsletter

Volume 13, Number 7
Nov 1989

Comments are Invited on Paper Standard Revision

A draft of the revised ANSI Z39.48 standard (Permanence of Paper for Printed Library Materials) is being circulated for comment and possible revision before balloting. The draft was prepared by NISO (National Information Standards Committee) Standards Committee II, which is soliciting comments both from NISO members and from other interested parties. Copies are available from NISO, P0 Box 1056, Bethesda, MD 20817, for $20. The comment period closes Jan. 16.

The new draft title shows how the standard's scope is being expanded: "Permanence of Paper for Publications and Documents in Libraries and Archives." It covers both coated and uncoated paper, and in several ways it addresses, more directly and knowledgeably than the 1984 version did, the concerns of librarians and archivists.

The draft is accompanied by an informative seven-page summary of the issues that were discussed during the revision of the standard. Because of the high level of interest in this standard, not only in this country but in Europe, permission has been obtained to reprint excerpts, comprising perhaps a third of the issues document, in the Abbey Newsletter.


...Given the relationship of durability tests to the determination of the relative permanence of paper, the following different approaches to establishing a standard for permanent paper are possible: (1) specify certain key characteristics of the make-up of the finished paper that have been identified as contributing to permanence by prior research; (2) specify a certain level of performance on a variety of physical tests applied after artificial aging of the paper; and (3) use some combination of these approaches. The current ANSI Z39.48 [i.e., the 1984 version] takes the first approach.

Criticisms and comments on the provisions of the current standard have centered on the requirements for folding endurance and tear resistance. Several different, and in some cases contradictory, arguments have been communicated to SCII [Standards Committee II]. The main arguments can be summarized as follows:

  1. Footnotes 3 and 4 make it unclear whether folding endurance and tear resistance are really part of the official standard. This should be clarified.
  2. Paper manufacturers do not routinely conduct these physical tests (particularly the folding endurance test) and therefore cannot certify that their papers meet these requirements. While papermakers can easily attest to pH, alkaline reserve, and freedom from groundwood in papers they produce, determination of folding endurance and tear resistance requires repeated tests. Results vary within the same papermaking run. The folding endurance test itself has tremendous inherent variability. These factors make physical testing expensive and time-consuming and also make some manufacturers reluctant to label papers as adhering to the standard.
  3. [No. 3 and 4 summarize objections to inclusion of durability specifications, especially without reference to intended use.]
  4. The requirements for folding endurance and tear resistance should be modified to include both minimum pre-aging values and a minimum percentage retention of those properties after artificial aging.... In the event that there are factors in the make-up of the paper other than acidity or groundwood that have a deleterious effect on permanence (e.g., certain metals, recycled pulp), durability tests after artificial aging will discover them....

After reviewing a variety of data, arguments, and opinions (many of which are summarized below), SCII decided that the basic approach taken by the drafters of the current Z39.48, which focuses on attributes of finished paper, remains the most practical to implement.

Durability Tests

... Since other tests [besides the folding endurance test] are also suitable for determining durability and both proponents and opponents of durability testing particularly dislike the folding endurance test, SCII proposes to remove it from the standard.

Tear resistance is another useful measure of durability Because SCII agrees that it is desirable for a permanence standard to specify a minimum initial level of durability, the Committee proposes to retain the tear resistance criterion. Testing of samples of currently made alkaline book papers suggests that most such papers can meet the tear resistance criterion specified in the current standard. The criterion does exclude some papers made with recycled fiber.

Artificial Aging

... It is not possible to conduct tests to determine exactly how long a particular paper will last. We are therefore not in a position to establish a standard for paper that will last a specific amount of time, e.g., at least 500 years. Artificial aging tests can, however, be used to determine the relative permanence of different papers; they have been used in this way to help to establish conclusively that alkaline paper is more permanent than otherwise comparable acidic paper.

... There are two main types of artificial aging currently in use: dry aging and humid aging. In dry aging, the paper is aged in an oven simply supplied with ambient air. Dry aging is cheaper and easier to do, but is considered by many to be less suitable than humid aging as a surrogate for natural aging. Humid aging requires more expensive equipment to maintain desired temperature and humidity levels during aging and careful adjustment of the humidity levels within the paper before the aging period begins. There has been some experimentation with aging paper after enclosing it in stoppered test tubes or encapsulating it. (Dr. Chandru Shahani of the Library of Congress is currently experimenting with encapsulating paper and then aging it in a dry oven.) These methods seal in the paper's moisture, thus allowing relatively rapid "humid" aging in a dry oven.

If the conditions and length of artificial aging appropriate to a standard for permanence of paper can be selected, there remains the difficult task of establishing appropriate minimum percentages for the retention of various

physical properties. Early guidelines suggested 50% retained folding endurance and 85% or more retained tear resistance after 24 hours of artificial aging. These guidelines were developed without data on the actual retention of physical properties by current, commercially-made alkaline fine printing papers, however. Much of the paper testing data available is derived from special hand-made test papers. More data on currently made coated and uncoated fine printing papers are probably needed before reasonable minimum values can be set for retention of physical properties after aging.

Given the number of questions that remain unanswered, SCII has concluded that it would be premature to add a requirement for artificial aging to this revision of Z39.48.

Maximum pH

The current Z39.48 specifies a minimum pH, but no maximum. Because papers with very high alkalinity are subject to increased oxidation, it has been suggested that a maximum pH be added. The first draft of the proposed ISO for permanence of paper included a maximum pH of 9.5. Tests done by the Library of Congress indicate, however, that commercial papers with pH levels as high as 10.3 are as permanent as papers in the 7.5 to 9.5 pH range.

Since commercially made alkaline papers do not appear to exceed a pH of 10, SCII has elected not to propose a maximum pH.

Mechanical Pulps

Since the current standard was developed, the paper industry has begun to use chemi-thermomechanical and other new types of mechanical pulps. These pulps do not contain groundwood and therefore meet the paper stock requirement in the current standard. Unfortunately, such pulps do contain substantial amounts of residual lignin, which is the most deleterious substance in groundwood. To avoid this problem, the Committee proposes to change the paper stock requirement to address lignin directly.

Recycled Pulps

Recycled paper is made with some percentage of pulp derived from previously made paper. Although to date recycled pulp has not played an important part in the production of fine printing papers, its role is likely to increase due to Governmental pressure, environmental concerns, and relative cost. Depending on the type of paper from which recycled pulp is made, the methods used to clean and prepare it, and the amount of mew pulp included with it, alkaline papers containing recycled pulp can be suitable for long term retention in libraries and archives. The concern is that the current Z39.48 is not adequate to distinguish quality recycled papers from weaker recycled papers [that] are also alkaline. Testing performed by the Committee indicates that the initial tear resistance criterion in the standard does discriminate among alkaline papers with recycled fibers, i.e., some alkaline recycled papers meet the tear resistance requirement and some don' t. The proposed revision will also screen out recycled paper with significant amounts of residual lignin.

Other Deleterious Substances

Many substances used in commercially made papers are potentially deleterious to permanence if included in sufficient amounts. Specific substances brought to the attention of SCII include titanium, copper, and aluminum. Given the basic approach of Z39.48 (which SCII proposes to retain), one can argue that a maximum allowable value should be included in the Standard for all such substances. To date, however, SCII has not found extensive data either on the presence of dangerous levels of such substances in currently made book papers or on their negative effects on permanence independent of the factors already addressed in Z39.48. In the absence of such data, the Committee has elected not to add such criteria to the Standard....

Coated Paper

.Paper testing commissioned for SCII has corroborated the view that the core of a coated paper must be acid-free to ensure reasonable permanence. Standard tests for determining the pH of the core paper exclusive of its coating are yet to be developed. For this reason, the proposed revision specifies reliance on manufacturer's certification of the pH of the core paper as well as qualitative methods for determining the core pH of coated papers....

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