Imagine pulling a book from the shelf and noticing the pages have yellowed since it was purchased. You open the book, only to see brown spots all over the title page. Confused, you close the book, and flakes of leather fall to the floor. “What happened to my book?” you wonder.
But books may be exposed to moisture or environmental air pollutants that interact with the parts of the books themselves. The interaction can lead to chemical reactions that can produce more acids, and thus, continue the process of degradation.
“Paper is primarily made up of cellulose fibers made from mashing down wood into a pulp,” Conservator Hillary Morgan explains. “The length of fibers in each sheet of paper help to determine its strength. Long-fibered paper is stronger and more flexible than short-fibered paper.”
As paper ages, these fibers can weaken or break down causing deterioration. The top two factors that influence this deterioration are the paper’s composition and the conditions of the paper’s storage.
The following are the three most common types of book decay you may discover on your bookshelf:
Paper oxidation, or why your book’s pages are yellowing
The yellowing of paper products can be attributed to paper oxidation. The paper we use today comes from wood, which consists of cellulose and a component called lignin. When exposed to light and oxygen, the molecular structure of lignin changes.
To varying degrees, both cellulose and lignin are susceptible to oxidation. Over time, oxidation alters the paper’s structure and related regions in the paper called chromophores. These regions reflect certain wavelengths of light that we perceive as color.
According to Live Science, paper manufacturers try to remove as much lignin as possible by bleaching the paper. The more lignin that’s removed, the longer the paper will remain light. Before the 1800s, paper was made from cotton and linen clothing rags, which don’t have lignin, reducing the likelihood of paper oxidation.
Foxing, or why your book’s pages are spotting
High humidity and damp conditions are the main culprits of paper foxing. Other factors, including traces of metal left behind by paper manufacturing, can result in an acidic environment on the paper.
Paper foxing is identified by telltale red spots, similar in color to a fox, hence the name. Foxing can also be mistaken for mold, which can be similar in appearance. Mold, encouraged by the acidic environment, will feed on the paper, as well as any organic materials left behind like dirt, finger marks, food stains, insects or metal debris as mentioned above.
To prevent foxing, avoid leaving books in environments where temperature and humidity can fluctuate like basements, attics and areas near radiators and vents. Perhaps the threat of foxing will lead you to reconsider leaving your books in storage!
Red rot, or why your leather-bound books are flaking
Red rot is associated with the fibrous structure of the leather itself. Its cause still remains somewhat mysterious, but conservators believe it comes from acidic reactions--particularly sulfuric acid. Sulfuric acid attacks and breaks down the protein chains that make up leather.
These acids could have been added to the leather during the tanning process or have formed from the absorption of the compounds often found in pollution. This material degradation is common among vegetable-tanned leathers from the late nineteenth and early twentieth centuries.
If left untreated, those flakes of leather falling to the floor can completely disintegrate, turning the leather into a powder-like substance. For treatment, conservators focus more on the prevention of further damage rather than repair. This could look like wrapping the leather book in acid-free paper and storing it in an archival-quality box.