Abbey Publications
Abbey Publications
Selections from North American Permanent Papers
Ellen McCrady <>

The ANSI/NISO Z39.48 Standard
and Other Standards

The word "standard" is used in many ways. In common speech, someone is said to be "setting a standard" when they achieve a high level of performance in some activity. In government regulatory activities, what people refer to as a standard may actually be a law. In between these two extremes lie voluntary consensus standards, the most common type. The ANSI/NISO standard is of this type.

Voluntary consensus standards are voluntary because you don't have to use them if you don't want to. They are called consensus standards because they are formed by consensus of interested parties (producers, consumers, and general interest members), rather than by edict, and also because their use is optional.

Standards organizations such as ANSI (the American National Standards Institute), ASTM (American Society for Testing and Materials) or ISO (International Organization for Standardization) have committees or allied organizations that develop their standards. NISO (National Information Standards Organization) works with ANSI, which coordinates American standards work. NISO, however, publishes and distributes its own standards when they are finished.

Paper standards developers will often commission some research and testing to see whether the specifications they are considering are actually met by products now on the market, and whether the specifications identify products known to have the desired characteristics (e.g., permanence).

ANSI/NISO Z39.48-1992

NISO, a standards developer serving the needs of libraries and information services, published the original Z39.48 standard in 1984, calling it "Permanence of Paper for Printed Library Materials." It was revised and its scope broadened in 1992. Now, for the first time, it covers both coated and uncoated papers. It uses metric measurement for the tear index. Fold endurance has been dropped, though tear resistance has been retained.

A summary of the main requirements of the 1992 revision, "Permanence of Paper for Publications and Documents in Libraries and Archives," is given below in tabular form. (Because the standard is a copyrighted publication, it cannot be quoted here in its entirety.)

For a copy of the 19-page standard, call NISO Press at 800/282-NISO [6476]. The price is $30, plus $5.00 for postage and handling. Payment may be made by credit card. Mail orders can be sent to NISO Press Fulfillment, PO Box 338, Oxon Hill, MD 20750-0338.

Requirement Uncoated Coated
pH: 7.5-10.0 Core paper: 7.0-10.0, provided that the paper as a whole meets the alkaline reserve requirements.
Alkaline reserve (CaCO3 equivalent): 2% minimum 2% minimum (for entire paper, including coating)
Tear resistance: Tear index: 5.25 mNm2/g Tear index: 3.50 mNm2/g
Paper stock: 1% lignin maximum (Kappa number no greater than 7) Same as for uncoated

pH. Most people interested in permanent paper are familiar with the pH scale, which runs from 0 to 14. It gives us a way of quantifying acidity and alkalinity. Anything below 7.0 (the neutral point) is acid, and anything above 7.0 is alkaline. There are several ways of measuring pH, not counting the more than 67 pH indicator fluids on the market. (A company that sells an immense variety of these fluids as well as test papers is Micro Essential Laboratory, in Brooklyn, telephone 718/338-3618, fax 718/692-4491.)

The most commonly used test methods for research purposes are the standard hot and cold extraction tests and the surface electrode, all of which involve a pH meter. None of them correlates perfectly with any of the others. Occasionally there will even be a difference of as much as 1.5 pH units for the same paper, most commonly found with hot and cold extraction results for alkaline paper.

There is nothing sacred about the neutral point. A paper with a pH of 7.1 is not noticeably more alkaline or permanent than a paper with a pH of 6.9. But generally speaking, the higher the pH (up to around 10), the longer a paper will last. Paper sized with the traditional alum and rosin tests around pH 4.5-5.0 when it is new, and it becomes more acidic as time goes on, because paper becomes more acidic as it deteriorates. Today's permanence standards usually specify a pH of 7.5 because this is about as low as calcium carbonate can get without breaking down and giving off bubbles. ("Acid tolerant" calcium carbonate is an exception. It has been treated to make it less reactive. This permits it to be used with slightly acidic pulp to make carbonate-filled groundwood papers.)

Alkaline reserve. The alkaline reserve of 2% calcium carbonate is just that: a reserve. It protects the paper against acidic gases by reacting with them before they can find the cellulose. It does not need to have a very high pH itself to do this, and its pH does not decline when it reacts with acids. If the calcium carbonate is used up by long exposure or high levels of pollutant gases, the paper will then deteriorate about as fast as it would have without the alkaline reserve. But it takes a long time to reach this stage: some papers made before 1550 still contain calcium carbonate, presumably from the hard water used by the mill, or from the milk used during sun-bleaching of the linen cloth from which the paper was eventually made.

Compounds based on magnesium or other alkaline earth metals instead of calcium could be used as alkaline reserves, but they are more expensive, and they are not popular with the paper industry. Magnesium is used in a number of formulas, however, for the deacidification of paper and books.

Tear resistance. The tear index is a simpler way of measuring paper's resistance to tear, because it consists of a single value that holds for all weights of a single paper grade. It is stated in millinewtons (mN, the force required to tear the paper) divided by grams per square meter (weight of paper). The ANSI/NISO standard gives a simple formula for conversion from the conventional to the new measure: Multiply the grams of tear resistance by 9.81 and divide the result by grammage (g/m2). An uncoated 50 lb. offset with a tear resistance of 40 grams (392 mN) would satisfy the requirement of 5.25 mNm2/g tear index.

Until now, fold endurance was also included in standards for permanence, because it is a more sensitive index of deterioration after aging, and it measures a different aspect of strength than tear. Because fold endurance is so sensitive to the effects of aging, the test paper can be aged for a shorter time in the oven. Labs in cultural institutions continue to use it, but paper mills do not like it because of the time it takes. A large number of test strips have to be run before the average value stabilizes.

Lignin content and choice of criteria. The first edition of this standard required only "no groundwood or unbleached pulp." This was an indirect way of excluding lignin, which degrades and discolors cellulose if it is not removed in the pulping and bleaching stages. The current edition is much more explicit and exact. It requires no more than 1% lignin by weight, as indicated by a Kappa number no greater than 7.

Research is now being done in several countries, under the auspices of ASTM's Institute for Standards Research (ISR), to find out whether calcium carbonate can protect lignin-containing paper from physical deterioration. (We already know that it cannot keep lignin-containing paper from yellowing, which is also a form of physical deterioration, since optics is a branch of physics.) Results of this work will not be available for another two years or so. It was begun on the initiative of the mechanical pulp industry, which is eager to see its product used in printing and writing markets now dominated by chemical pulps.

New permanence standards permitting more lignin in permanent paper will probably be proposed when the results are published, since preliminary findings do show good retention of strength for carbonate-filled high-lignin paper. Whether the new standards will be based on accelerated aging tests (as the German standard, DIN 6738, is) or on paper composition (as U.S. and ISO standards are) is not known at present. The pulp industry favors the aging test option, which they refer to as "performance."

Whether the mills would be willing to age-test their papers as often or as carefully as consumers might like remains to be seen, however. Age-testing is expensive and time-consuming, and would have to be done in addition to the tests called for by present standards-not instead of them. It also remains to be seen whether the public will trust the standard, especially since few institutions will have time to test samples and age them for a week before accepting a large shipment. (After DIN 6738 was published, German librarians revolted against it and published their own standard, based on composition.)

Another cause for skepticism about permanence standards based on oven aging is the opposition of the fine paper mills, the ones that use chemical pulp. Some of them include recycled pulp in their papers. If the waste paper from which it is made includes some of the new "permanent" paper that is made with mechanical pulp (which it will, since new papers of both sorts look exactly alike to start with), what will happen to that mill's reputation for quality? Their own super premium papers will start to yellow, and this will not be easily accepted by the average customer.

Standards for other materials like house paint, which are expected to last a long time, often specify some permanence criteria, but these may include both accelerated aging tests (e.g. aging in sunlight) and identification of required, permitted or forbidden components.

Other Permanence Standards

ISO. The International Organization for Standardization (ISO) approved a standard in 1993 (ISO 9706 - Information and Documentation - Paper for Documents - Requirements for Permanence). Its provisions are very similar to those of ANSI/NISO Z39.48-1992, but its requirements for tear resistance and maximum Kappa number ("resistance to oxidation") are slightly different (5, rather than 7).

ASTM. The American Society for Testing and Materials has had four standards for permanent office papers since the mid-1970s:

D 3208 - 94, Manifold Papers for Permanent Records
D 3290 - 94, Bond and Ledger Papers for Permanent Records
D 3301 - 94, File Folders for Storage of Permanent Records
D 3458 - 94, Copies from Office Copying Machines for Permanent Records

Each of these standards is actually six standards in one, incorporating three levels of permanence, each of which has two levels of durability. The three permanence types have different minimum pH values (pH 5.5 to 7.5). Type I ("maximum permanence") is the only one requiring an alkaline reserve, 2% calcium carbonate. The two "grades" or strength levels have different requirements for tearing resistance and sometimes also for folding endurance. Photocopy papers (D 3458) must retain 80% of their folding endurance after accelerated aging for 72 hours at 105°C. Aging is necessary because some photocopy papers are coated, and the usual hot or cold extraction tests would give misleading results. D 3458 also has requirements for brightness, opacity, fluorescence, and for information that must appear on the order. The other standards do not require accelerated aging, but all have a large number of requirements compared to the ANSI/NISO standard.

In 1996, two useful guides were added to the ASTM list:

D 5634-96, Guide for Selection of Permanent and Durable Offset and Book Papers
D 6034-96, Guide for Selection of Permanent and Durable Artist's Paper

Both have the status of standards, but instead of specifications, they are guides, addressed principally to the knowledgeable consumer. The first guide is ASTM's only standard for printing paper. It provides background information, defining terms in context, and even giving the results of strength and aging tests done on a generous random sample of papers purchased in the marketplace. The second guide is necessarily less specific, since there are so many ways that artist's papers can be used, but both are informative and both have bibliographies of papers and other sources on permanence research.

Other standards. Canada, Australia and other countries now have standards for permanent paper. Now that ISO 9706 is finally published, many countries are expected to adopt it as their own. This is a common practice.

The Archives of Australia reported in September 1997 that since 1995 they had been testing archival enclosures for compliance with the Image Permanence's Photographic Activity Test (P.A.T.). They intended to cover all commercially available enclosures used by Australian collecting institutions.

Finland has a permanent paper standard, and about fifteen years ago the government was known to be testing papers submitted to it, to find out if they met the standard. A list of papers meeting the standard was being published and updated by the government.

ISO 11108 is a standard for "archival" (super permanent) papers. It specifies only fibers of cotton, hemp, ramie or flax (no wood), and in addition the paper must meet all the requirements of ISO 9706. Other standards are close to completion: ISO 11798, on permanence and durability of text images from writing, copying and so on; ISO 14416, on library binding; ISO 15659, on archival board; and ISO 11799, on environmental storage conditions.

North American Permanent Papers

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