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“This book stinks¹!” is really a bad review. But even a classic work can start to smell when it gets old enough. Now chemists have developed a technique that identifies what kind of degradation² process an old book or historical document is going through, based on the odors it gives off. The report appears in the American Chemical Society journal Analytical³ Chemistry.

An old book’s familiar musty smell is due to hundreds of different volatile⁴ organic compounds gassing out from the paper and other materials, such as the binding⁵. The particular blend of compounds results from specific degradation pathways. Conventional analysis techniques require small samples of the work for testing, further damaging the book. But analyzing⁶ the gases coming off the old books is noninvasive.

The researchers identified 15 organic compounds that make good markers to track the condition of books. They note that their system could be used to evaluate the type of document, its present condition and its likely future, thus helping⁷ preservationists map a strategy to save historical works.