Although most people in conservation are largely self-taught and are sometimes a little nervous over the adequacy of their training, they should gain confidence when they read the passage reproduced below from the ASHRAE Handbook: Applications, 1978, Section (A) 3.9. (The American Society of Heating, Refrigerating and Air- conditioning Engineers is a professional organization of engineers, one of whose functions is to codify standards for environmental conditions in buildings.)
"Paper used in books and manuscripts prior to the eighteenth century was a very stable material that wasn't affected much by the room environment. Paper was produced by cottage industry in small lots by breaking down the wood fibers by stamping, using naturally alkaline water from mountain streams, and applying a gelatin size. The need to reduce costs and increase production lead to industrialization, in which the wood fibers were cut with steel knives in a Holland machine, ordinary water was used, and rosin sizing was substituted for gelatin sizing. The result of these production changes is a paper that is susceptible to deterioration because of the acid content in the paper and sizing; for archival preservation, this paper should be stored at very low temperatures. It has been estimated that each 10 deg F (5.5°C), dry-bulb, that the room temperature is lowered will double the life of paper and that any reduction in humidity will also lengthen the life of paper. Libraries, however, house more than books; they are media centers which also store and use films and tapes. One will reach the dessication point for microfilms and magnetic tapes if the relative humidity is allowed to drop below 37% rh. This then becomes the lower limit for relative humidity in libraries, with the optimum humidity just above this point to minimize paper deterioration due to humidity. The upper limit for humidity when the room dry bulb exceeds 6S F (18.3°C) is 67% rh because mold forms above this point."
This passage was brought to the attention of the PLMS Committee on Physical Quality of Library Materials meeting in January by Pat Gladis, who had been referred to it by someone who was worried about the supposed "dessication point" of 37% RH for microfilm. The 1982 edition of the Handbook shifted the passage to Sec. (A) 3.11, Building Contents, but did not correct it. As it stands, it should take a prize for errors per square inch. There was talk at the committee meeting of forwarding a revised and corrected version to the editors of the Handbook.