Making Books Fit for the Future: The National Library of Poland
When I visited the Centre de recherche des monuments hisoriques in France, I saw the use of Metrohm instruments in the field of conservation of cultural heritage for the first time. In Warsaw, I got to see another application in a similar field: at the National Library of Poland. The paper used in books produced in the 19th and 20th century has a tendency to become yellow and brittle. Conservators at the library are working hard to identify these books and save them from falling apart.
Paper production was industrialized in the 19th century. At this time, people started using wood pulp to make paper instead of, for example, cotton, linen, or wool rags. While the industrial paper production process allowed the mass production of books and thereby helped to eliminate illiteracy, the quality of the paper was rather poor. The fibers in wood pulp, which are made from cellulose, a glucose polymer, are shorter than those in textile fibers, making the paper less flexible and less durable.
In the mechanical production of wood pulp, wood is simply ground up with all its components. One of them is lignin, another polymeric component of plant cell walls, which binds the cellulose fibers together and thereby makes them stable. Lignin, however, promotes acid hydrolysis, which will cut the fibers in the paper even shorter and, at the same time, produce more acids. This speeds up the deterioration of paper more and more.
This problem has been solved in today’s paper production, as most papers produced today are acid-free. However, books stemming from the 19th and 20th need to be deacidified in order to conserve them. The first step of this process is identifying the affected books. When the deacidification project was started, the conservators at the National Library of Poland didn’t know which books—and how many of them —would be affected. So they picked random books and analyzed their pH value. Now that hundred thousands of books have been analyzed, the conservators at the National Library of Poland have come to the conclusion that 97% of books from the period that they’re looking into are affected and require deacidification.
Of course, the conservators can’t cut up the original books to analyze them. So they place little pieces of papers inside the books until these have adapted the pH value of the book. Then, they cut them up into little strips and prepare a sample solution from these to measure the pH.
When a book is identified as acidic, it’s lined up for deacidification. The library has a dedicated setup for this purpose called Bookkeeper. The books are mounted on racks and placed in large tanks that are filled up with a deacidification solution. As water would damage the paper, this solution is water-free. The active ingredient for the deacidification is magnesium oxide.
During the entire process, the deacidification solution is stirred to make it enter the books and work its magic uniformly on all pages. After the deacidification, the solution is simply left to evaporate. The books come out of the tank undamaged—the only sign left of the process is a thin layer of magnesium oxide powder, a completely harmless substance. The books are now fit for times to come!