In his note inquiring about the value of music catalogs he owns, Rob
Goodale mentions that he has put one in a protective plastic envelope.
I want to caution him that there is "good" plastic and "bad" plastic.
The bad can do more harm than good by imparting some of its deleterious
ingredients to the paper. The Library of Congress uses Mylar for the
purpose, and immediately removes any ordinary polyethylene wrappers in
which items may come to the Library.
This is not the list for a discussion of paper preservation, but I will
add this: substances that cause the deterioration can be internal or
external to the paper. Cheap commercial paper of the pre-World War II
era has a high lignin content and also tends toward high acidity.
These can cause paper to self-destruct. Today's newsprint is an
example of this kind of paper; you can see what happens to it by
holding on to it for a year or so or by just setting it out in the
sunlight for a week.
External factors include such airborne compounds as CO2, which combines
with the natural moisture in the environment to cause acid destruction
of papers, and may also include anything the paper lies against or
contacts. Therefore it IS a good idea to encapsulate or envelope
valuable single sheets.
Simple steps you can take to protect your valuable documents are to
keep the paper cool, out of humid environments, and shielded from long
exposure to light (daylight or artificial). One trick is to enclose in
the envelope with the document a piece of alkaline paper which will act
as a sacrificial element to whatever acidity is in the paper or in the
environment -- or, better, you can use an alkaline envelope of the sort
made for archival storage. (I could supply Rob with at least one such
envelope (Lig-Free Type I, pH 8.5, buffered)).
Paper conservators will actually treat valuable documents by soaking
them in a buffering solution which both neutralizes the acidity in the
paper and renders it sufficiently alkaline to be self-protected against
environmental acidity for some time into the future. Once paper is
allowed to become brittle a whole set of different and costly
conservation procedures are required.