"A Comparison of Three Durability Standards for Paper," by R. van Deventer, J. Havermans and S. Berkhout. Restaurator 16 #3, 1995, p. 161-174.Reviewed by Ellen McCrady
The authors compare the paper permanence standards of ISO, the Netherlands, and Germany (ISO 9706, NEN 2728 and DIN 6738), feature by feature. They test five different papers (unsized sulphite, unsized cotton linter paper, archive quality permanent paper, alkaline copy paper and acid copy paper) by these standards, and evaluate the outcome.
It is not easy to understand all of the work reported or all the conclusions, because of typos and unclear translation and presentation of the data. The highest DIN life expectancy class is given as both "LDK 28-85" and "LDK 24-85"; the term "hard-ness" is offered as a synonym for "lignin content"; and the maximum kappa number in the ISO standard is given as 2, whereas it is actually 5 (however, all of the test papers had kappa numbers under 2! Is it possible that kappa number and percent lignin were confused?).
The authors seem to believe that the aging of samples for the DIN standard for 6, 12 and 24 days must be done sequentially, and that it would therefore take 6 + 12 + 24 days; but why couldn't the first batch be taken out after 6 days, the next after 12 days (i.e., 6 days later), and the last after 24 days (i.e., 12 days later)?
One of the conclusions is that for ISO 9706, "the minimum demand of the kappa number is too low." What does this mean? There is no minimum kappa number in the standard, only a maximum. Does it mean that the kappa number requirement could have been more stringent, given that all the experimental papers (supposedly) met it?
Despite the inexactitude here, the comparison among the three standards is eye-opening. All three standards require about the same pH level, though the DIN standard's pH requirement is described as implied; same with the alkaline reserve. All require a certain tear resistance, but the DIN standard's minimum value is only 1/8 that of the NEN (Netherlands) standard's; the authors note that tear resistance is not well suited for use with an aging requirement, because it declines so little with aging. The NEN standard is the only one with a fold test, and the DIN standard is the only one with tensile strength and stretch at break. The NEN standard is the only one that requires both an accelerated aging test and realistic chemical and mechanical tests. The authors prefer it over the other two, recommending that pH and alkaline reserve be measured again after aging. (3A9.6)