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The bitter truth about acid

By Robert Colver
Source: O.P. World, July 1998


It’s become a buzzword. People who don’t know anything else about book repair and conservation know to ask “Are the materials acid-Free?” They may not even know why it’s important; they just know that it is.

Around the world, books in the tens of millions are literally turning into dust on the shelves—or have already turned to dust. And the more ephemeral items like maps, letters, and documents probably exceed that number. It is indeed a crisis. But the best that conservation technology and chemistry can presently throw at it is only succeeding in controlling the problem at an arithmetic rate while the deterioration continues at a geometric rate.

Libraries and archives are obviously the frontline of defense in this battle. But book dealers and collectors, as temporary custodians of books, need to be familiar with what acid damage to paper is and when and why it started. If nothing else, it might keep you from investing heavily in a book that will crumble to dust before you can sell it or would cost too much to stabilize and repair.

So here goes... the bitter truth about acid.

Oddly enough—and fortunately—older paper is more immune from acid damage. I have a leaf from a Von de Spira, published in Venice in 1473. The paper is as supple, crisp and flexible as the day it was printed. Meanwhile, a few years back, I repaired a scientific tract printed in Petrograd in 1912. I had to lift out each individual page by sliding a sheet of plastic under it, because if I tried lifting by an edge or a corner, the paper disintegrated in my fingers. Why?

Prior to the Industrial Revolution, all paper was handmade, usually from a pulp made of linen rags, until the invention of the cotton gin in 1793 made cotton cost-effective. Papermakers usually started with white or at least light cloth, because prior to the discovery of chlorine in 1774, the available bleaches weren’t really strong enough to take the color out of colored rags. The water papermakers used was largely free of chemical pollutants. In fact, there’s a theory that my Venetian sheet is as healthy as it is because Italian papermakers used the water that trickled down from the mountains—the same mountains where all the Italian marble was quarried—and was saturated with calcium carbonate, a natural buffer.

With the discovery of chlorine, papermakers could dramatically increase their output and lower their costs by using cheaper grades of rags. So until shown the error of their ways, they tended to use it to wretched excess. The problem with chlorine bleach—either in making paper or in using it to bleach out foxing or library stamps—is that unless the chlorine is thoroughly washed out and neutralized, whatever remains combines with the moisture naturally present in paper and the atmosphere to form hypochlorous acid, which destroys the cellulose fibers that make paper behave like paper. Bye-bye book!

Power printing presses, developed early in the 19th Century, made books cheap enough for the masses. But they had an appetite for paper that would have turned Europe and America into vast nudist colonies if paper had continued to be made from cloth. Industrial papermakers took some 18th Century experiments in using raw plant fibers, like straw and wood pulp, and put them into commercial production. They started with the easiest way, simply grinding wood to dust, mixing it into a pulp with water, and then running the pulp through a machine to make one huge continuous sheet of paper. Problem solved?

Problem created! Wood naturally contains a substance called lignin. Lignin, exposed to oxygen and light, forms a powerful organic acid which destroys the cellulose. And here we go again! Fortunately, the reaction was so immediate, they caught onto it relatively quickly. (Test it yourself. Leave a newspaper on the back seat of your car in the heat and sunlight for a couple days.) So papermakers began cooking their wood chips in chemicals such as sodium hydroxide, sodium sulfate and sulfite of lime to break down the fibers to pulp. This got rid of most of the lignin. And, if the papermaker was paying attention to his product as well as his bottom line, most of the harmful chemical residues were washed out of the pulp or neutralized. Problem solved?  

Problem created! Paper, before it can be printed or written on, needs to be sized—given a hard surface so that ink doesn’t simply wick out and blur into, the fibers like blotter paper, which is nothing more than unsized paper. In the days of handmade paper and early in machine-made paper, sizing was gelatin, made from boiling out animal hides, hooves and tendons, applied in a separate step at the end of the paper- making process.

But by the l830’s, the demand for sized paper was exceeding the supply of dead critters. Harking back to the 18th Century experiments in plant-fiber paper, papermakers found that readily available rosin made an excellent sizing. And rosin didn’t have to be added as a separate step in the process. Problem solved?

Problem created! Rosin didn’t really like to bond to wood pulp. And it was water soluble, which kind of defeated the purpose. Enter alum—good, old pickle-making aluminum sulfate. Added to the pulp-rosin brew, alum acted as a catalyst to bond the rosin to the wood pulp and make it insoluble. If you didn’t put enough alum in, however, nothing happened. So papermakers erred on the side of putting too much alum in. Problem solved?

Problem created! Alum itself is acidic. Plus, it doesn’t know when to stop catalyzing. So long after the book is on a shelf, the alum is helping chemicals in the paper and the atmosphere form acids. And by now, we know what acids do to cellulose fibers.

The real problem was that, unlike the lignin damage which sort of blew up in their faces, the alum damage was on a long, slow fuse. After years of using it, nothing seemed to be wrong, so they continued using it.

In fact, most of the acid deterioration to paper is apparently relatively recent. Instead of happening in a neat straight line, it’s gone on a curve, rapidly escalating in the past few decades. And continuing to escalate.

To compound the problem, remember that for most of the last half of the 19th Century, beginning about the time wood-pulp paper came into common use, nearly every home and library was lit by gas. And this wasn’t nice, clean methane piped up from Louisiana. It was usually “town gas,” produced locally by gasifying coal—really cheap, low-grade, highly sulfurous coal. It came into the house full of moisture, was ignited, and began pumping into the atmosphere everything that’s needed for the rapid production of acid: water vapor, heat and unburned sulfur particles. For half a century, just about every book in the Western World was bathed in a daily shower of acid mist.

The year 1850 is usually used as the watershed for most books being produced on wood pulp paper with alum/ rosin sizing. Since then, just about every book has been printed on acidic, self-destructing paper. Bibles and other books on similar thin paper fared better. Paper made that thin needed to be “loaded” to increase its opacity. And the material mixed in with the pulp to load it was usually a white, calcium clay, which, by blind luck, acted as a buffer against acidity. A similar clay is used to provide the glossy surface on coated stock for photo and art books. But the clay outside on coated stock from earlier in this century didn’t necessarily prevent the deterioration of the paper underneath, and it can be as brittle, if not more so, than its uncoated cousins.

Most university presses began using alkaline—non-acidic—paper as soon as it became readily available. Being universities, they believed in the permanence of the printed word and were in a position to say “hang the extra cost.” Despite pleas and howls from librarians and conservators, trade publishers didn’t routinely begin using alkaline paper until about a decade ago, even though the cost differential had been virtually eradicated.

And oddly enough the deciding pressure didn’t come from librarians, but from the other end of the food chain. Members of various authors’ guilds pressured their publishers with “I’m writing stuff I want people to read 200 years from now and you’re putting it on paper that’s going to be dust in 50 years. Start printing me on permanent paper or I’ll find a publisher who will!”

It worked!

Barring a groundswell of demand, I’m not going to get into the gory details of deacidification, paper restoration and encapsulation. It can be a good sales point sometimes to put “deacidified” in the catalog of a particularly valuable item. And it will earn you points at the Last Judgment. But other than an occasional single document or map, it’s not something you want to undertake in-house. And it’s arguably the responsibility of the end owner, not the dealer.

If you do see “deacidified” in someone else’s catalog, just be aware that doesn’t mean the document, map or print in question won’t fall apart in your fingers the minute you try to pick it up. Deacidification only stops ongoing deterioration and prevents further deterioration. It doesn’t reverse any damage already done. Alkaline dust is still dust.

The main thing I hope you take away from this is: A brittle item is, practically speaking, always going to be brittle. Putting brittle pages in a new or restored binding won’t change that—and it may make it worse. Mounting a brittle map behind even acid-free mat board doesn’t mean it’s not brittle. A brittle document in a Mylar envelope may still crumble if you battle static electricity to get it out of the envelope.

The item will always require careful handling—by you, by your customers, and by the buyer. Put a brittle book on the shelf or out at a fair for very long and I can almost guarantee you’ll have a rather expensive repair job on your hands.

Assuming, of course, that the title page doesn’t break off and get lost!

Bob Colver owns Ram’s Head Bindery in Durham, NC. He’s been mending books for the antiquarian book trade for 12 years.