For Millions of Old Books, Acid Is the Silent ‘Killer’ : Libraries: About 80% of any research collection faces deterioration danger because of acidification of paper. But a new coating process is under study.

Over the next three months, it is estimated that more than 3.5 million of the nation’s 300 million research library books will silently decompose and die as a result of acid contained in their pages.

“If you walk in the library there is a distinctive odor, and you know it’s the odor of disintegrating books in the stacks,” said Scott Bennett, director of the Milton Eisenhower Library at Johns Hopkins University.

Roughly 80% of the collection in any given library is thought to be acidic and in danger of deterioration because most books have been made of paper that contains aluminum sulfate, a stiffening agent that starts breaking down the paper in as little as 50 years. Heat, humidity and air pollution accelerate the process.

University and research libraries are most affected by acidification because they have larger collections of old books than other institutions.

“It is a very serious problem here, in part, because it is such an old collection,” said David F. Bishop, librarian of the University of Illinois at Urbana, which has a collection of 7 million volumes. In varying degrees, acidification has affected a majority of the collection, he noted.

And the problem is not likely to go away soon because only 30% of the paper made today is acid-free. Only a relatively small number of publishers--mostly encyclopedia, textbook and university presses--who are more concerned with having their books last for generations use it.

Until recently, methods to combat the deterioration were expensive. The average acquisition cost of a replacement book is $125 and the cost of processing a book onto microfilm is between $100 and $125.

But a new process that has recently been patented, Diethl zinc, has drawn widespread praise from experts in the field for its effectiveness and its relatively low cost--about $6 a volume. The process, developed jointly by the Library of Congress and Akzo Chemicals Inc., coats books with a thin layer of zinc oxide in a special gas chamber. Although DEZ prevents further decay from taking place, it cannot reverse acidification that has already taken place.

After being treated, the average book is expected to last as long as 500 years in contrast to an untreated book, which has a life expectancy of 50 to 100 years.

“I believe it is by far the best documented process available for de-acidification of paper,” Bennett said of DEZ, which Johns Hopkins will begin using in a few months on its collection.

However, there are some questions about the method. Bishop said he believes DEZ is sound, but has some safety concerns. “It deals with very volatile chemicals and so it’s something I wouldn’t want in my building, and I would want it handled by professionals,” he said.

Although the Library of Congress was one of the developers of the DEZ process, it is still searching for other ways to solve the problem. Donald Wisdom, of the Library of Congress’ preservation department, said the library will be seeking bids later this spring on mass de-acidification of its collection. About 77,000 books in the library become brittle or crumble to dust every year, according to a study by Akzo.

The two forms of de-acidification commonly used by libraries now are a liquid chemical bath--known as Wei t’o and gas infusion. Only the liquid bath method has been used on a wide scale.

Wei t’o--the name is derived from a Chinese god who protected books--involves spraying liquefied magnesium carbonate on individual books enclosed in a small chamber. For the system to be used on a large number of books, a special facility must be built close to the library in which the books are stored. One of the drawbacks of the system is that the process releases chlorofluorocarbons into the atmosphere, which break down the ozone layer. Another is that not all books can be treated by this process. Certain inks run, materials with plastic bindings cannot be treated and large materials do not fit into the processing chamber.

The gas infusion method, which is similar to DEZ, coats the books with gas in a chamber, but there have been problems with some treated books returning to an unacceptable acid level, as well as book covers becoming stuck together.