I have noticed large variations in the quality of paper used in old books and magazines, even within a single copy. The poorer quality paper turns brown with age, while the best quality stays white. This is due to acid content in the paper, and is essentially a slow oxidation - the paper is gradually "burning" and turning to ash.
The poorest quality paper is newsprint. You may notice that a newspaper may start turning brown within a few weeks, and the paper in very old ones is often so dark that it is difficult to read what is printed on it. Paper in that condition is usually very brittle as well. You can duplicate the effect by putting the paper in an oven and baking it at a temperature below the incendiary point.
I have a couple of ARRL Handbooks printed during WW2, when material was often hard to get, and they had to use what was available. Whole sections of that handbook are almost dark brown, while other sections look brand new right off the press. The sections are random, but come in adjacent blocks of maybe 100 pages.
I have multiple copies of some issues of
RADIO, and interestingly, the same issues sometimes all show a lot of discolouration. Sometimes, certain pages in some issues are worse than other pages, but in every copy of a particular monthly issue, the same pages show the most deterioration while the same pages in all the copies remain in best condition. Apparently, the printer used different batches of paper of widely non-uniform quality when running off the pages of an issue, so the variation in paper quality may be identical in every copy of that particular issue.
And every copy of some issues shows more deterioration than every copy of other issues.
But some of the deterioration is environmental, since the yellowed pages of one copy may be almost brown in another. Most of the browning occurs around the edge of the page. Evidently heat and humidity accelerate the change.
Unfortunately, acid paper became popular in the early 20th century because it could be made cheaply. Much like newspapers, magazines were never intended to be preserved beyond a few months of their publication, so little care was given to the use of good quality paper. But regardless of quality all acid paper is destined to disintegrate over time.
But not only newspapers and magazines were printed on acid paper; the so were the majority of hardbound books of the same era. Much of the existing human knowledge is now archived on acid paper, and if some effort is not made to preserve this material, this knowledge will be lost as the paper it is printed on self destructs, just as certainly as the vast amount of knowledge that was lost in the fire at the great
Alexandria library.
Some of my 1930's magazines were in mint condition when I first acquired them in the late 60's and early 70's. But now, they are twice as old as they were when I first got them, and many of the same copies are seriously turning yellow and brown, and becoming brittle. In another generation or two, the paper will become so fragile that they will no longer be able to be handled without falling apart. Some of my pre-1936
RADIOs are already in nearly that condition, while some pre-1936
R-9's show absolutely no signs of deterioration.
http://www.britishorigami.info/academic/lister/acidpaper.htmHere is another example of concern over this issue:
Printed volumes of the New Zealand Statutes between about 1885 and 1900 are about to shatter and be lost forever.
The paper deterioration process is a time bomb which could see this country suddenly deprived of significant statutes such as the Land and Income Assessment Act 1891 and the Native Land Act 1894 - a whole chunk of history, of interest to Maori and to historians, as well as to the legal profession.
It is sobering to think that archives of New Zealand as a nation are on this acidic paper and will be turned to dust a century from now if something is not done.
The problem is caused by acid contained in the paper on which the statutes are printed. The acid causes it to darken over the years, become brittle, and break into pieces on handling. The process cannot be reversed and many of the remaining statutes of this era in libraries are already completely unusable.
http://www.adls.org.nz/profession/lawnews/2004/issue06/march37.asp