Acid-Free, Lignen-Free, and Buffered Paper Explained! (addendum)

Here is more information on acidity in paper:

This is a "sidebar" article to the main article about acid, lignen, and buffering which I wrote on posted at July 3, 2005. I found an interesting report at AskPhil.org, a site maintained by the Collectors Club of Chicago -- these are stamp collectors, whose stamp albums can have not just great personal significance, but also potentially great financial value. (I assume that "Phil" refers to a philatelist, not someone named Philip.) The report defines these terms (among others):

• Acid: A chemical compound having a pH below 7.0. Acid [acidic] paper contains rosin and alum. This combination of chemicals is used as a "size" to impart good writing and printing properties to the paper. Unfortunately, the alum is acidic and over a period of time destroys the integrity of the paper. The acid affects not only the fibers of the paper, but sometimes the inks and colors on the paper.
• Acid Free Paper: A paper manufactured under neutral or alkaline conditions with a pH greater than 7.0 containing no acidic additives.
• Alkaline Reserve: The presence of calcium carbonate or other alkaline material in paper capable of neutralizing acids as they are formed.
• Buffer: In our context, an alkaline reserve, usually calcium carbonate, added to paper.
• Lignin: The noncarbohydrate portion of the cell wall of plant material that varies in composition with type of species, age, growing conditions, etc. of the plant. Lignin reverts to its natural brown color on exposure to light and produces peroxides on aging, which deteriorates any paper exposed to them. Complete removal of lignins requires harsh chemical treatment of the wood fibers, which can reduce the strength of the paper.
• pH: This is the most important figure as far as collectors are concerned. Technically, it is the negative logarithm of the hydrogen ion activity in an aqueous solution measured on a scale of 0 to 14. Numerically expressed, pH 7 is neutral, lower numbers are acidic, higher numbers are alkaline. However, pH 4 is ten times more acidic than pH 5 and one hundred times more acidic than pH 6. There is no such statement as a "little acidic;" it is either acidic or not.

So what happened? The paper got less acidic over time. The most acidic page tested, with a pH of 9.34, also had a relatively high "alkaline reserve," which brought down the pH level to 7.22 after "artificial aging" of 150 years. But the acid level went down with aging even for paper with an "alkaline reserve" measured at 0.0!

All of this raises the question: Does acid content really matter? Of the __ pages tested, before aging, 17 were "acidic" and 47 were not. But only 24 of those papers were "artificially aged" -- 17 of these were acidic before aging, but only 10 were acidic after aging.

That surprises me, because some salespeople have told me that paper usually becomes more acidic over time. Perhaps they were referring to "acid-free" scrapbook paper that has been exposed to more acidic papers (for example, a newspaper clipping glued to the page).

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