Several levels of permanence have been arbitrarily established. In descending order, they are:
1. The greatest degree of permanence obtainable, within the limits of present-day technology. These papers would be used for state or other archives, treaties, political records, etc. This quality of paper would be manufactured from 100% rag (new linen), flax, cotton, or hemp, undyed and unbleached, and produced by hand or machine. It would contain no loading or color additives, and beating and drying would be controlled so as to obtain maximum folding and tearing strengths. The physical and chemical criteria of permanence would be:
pH value—minimum of 7.0, maximum 9.5 acidity—maximum of 0.04% folding strength decrease after 72 hours at 100° C.—maximum of 25% alpha cellulose content—minimum of 95%—decrease after 72 hours at 100° C.—maximum of 1.5 copper number—maximum of 1.2; maximum after 72 hours at 100° C.—.5 rosin content—maximum of 1.2% iron content—maximum of 0.005% chlorine content—maximum of 0.05%
2. Intermediate level, providing a high degree of permanence, yet considerably lower than that of the highest level. This type of paper would be used for important documents, including letters of government officials, and special editions of books intended for permanent retention (and which are to be retained under the best of environmental conditions while still being made available to readers). This class of paper would consist of 100% rag (clean, undyed rags of linen, cotton, or hemp), with any materials used for coloring to be as lightfast as possible and free from acid. The maximum decrease in folding endurance after 72 hours at 100° C. should not exceed 30%, and the alpha cellulose minimum should be 92%.
3. The lowest level, used principally for printing first editions, issues of important books, periodical publications, important reference books, and the like, all of which will be stored under relatively good storage conditions. This paper would consist of 30% rag, mixed with 70% carefully bleached sulfite wood pulp, or 35% wood pulp and 35% other fiber, e. g., esparto, straw, etc.; maximum ash content to be 10%, except for coated and other special papers required for color printing, etc. The coloring material would not be poorer in light fastness than ultramarine, or poorer than Prussian blue in its resistance to acidity. Alpha cellulose minimum would be 87% and the maximum decrease in folding endurance after 72 hours at 100° C. would be 40%. Other specifications would be the same as the intermediate type.
These specifications do not of course have any bearing on the permanence (or lack of it) of papers already in existence. The prevailing opinion today seems to be that any paper can be made more or less "permanent" by the addition of a suitable alkaline reserve. Modern papers containing, for example, at least 3% (by weight of the paper) of calcium or magnesium carbonate are sometimes classed as archival, since they are expected to last in the range of 300 to 500 years. The addition of an alkaline reserve into any given paper, however, will not restore strength to the paper if it has already been weakened by deleterious influences, either during manufacture, or thereafter. Furthermore, the length of time an alkaline reserve will retain its effectiveness depends, at least to a certain extent, on the level of pollution in the atmosphere, and the quantity of harmful chemicals added to the paper during manufacture. Finally, while an alkaline reserve may retard or prevent chemical deterioration, it has no influence on the fundamental durability of the paper, i.e., its inherent strength, which is enhanced, for example, by the use of long-fibered stock, and decreased by the use of excessive loadings, filler clays, etc. (17 , 143 , 198 )