The smell of old books is as ubiquitous and memory-jogging as that of cut grass or freshly baked bread. It instantly transports us to musty college libraries, second-hand bookshops sliced by shafts of light thick with dust mites, and the well-turned, softly yellowing pages of our favorite novels – re-read and re-thumbed down the years. It’s a sweetly pleasant and nostalgic odor that seems like it should have a specific word to describe and encapsulate it – like petrichor for the smell of fresh rain on dry soil. But far from being a traditional and harmless olfactory enhancement of the reading experience, the smell is actually a marker of decay.
Paper is an organic material, and with age the components are broken down by acid hydrolysis, giving off volatile and semi-volatile organic compounds (VOCs) into the air, which may have hints of vanilla (vanillin), almond (benzaldehyde) or musky florals (ethyls, tolulene, and hexanol). The rate and pattern of decay and VOC emission that make up the particular blend of smell varies according to the original composition of the paper, ink and binding in each tome – as well as how the paper has been stored and used over the years. Key factors include the presence of lignin, rosin and ash, as well as the acidity, degree of polymerization and protein content.1,2 Paper may also take on smells from its immediate environment, including cigarette smoke, cooking vapors, damp and molds or flowers and perfumed love notes pressed between the pages.
Research into this area by the food and pharmaceutical industries has focused on preventing VOCs from paper and cardboard packaging seeping into products, but there is also an important non-commercial consideration to the chemistry of paper degradation, and libraries and archives are now looking to VOC analysis and a technique known as material degradomics to help monitor the condition of their collections, and to develop effective long-term conservation treatments and plans for books and texts.2 This method essentially ‘sniffs’ the paper to determine the volume and composition of the VOC profile, a far less invasive method of analysis than those used previously which required the removal of pages for diagnostics in the lab – an act just as destructive as the natural decaying process itself. Rapidly degrading and at-risk documents that are identified by degradomics can be treated or neutralized in large reactors to balance their acidity and slow the decay. Research has also helped to show that archives should have decreased temperature and relative humidity in order to preserve paper-based collections for longer.1,2
There may be no immediate concern for very old conserved texts – despite its organic makeup, paper can be a very durable material if produced and stored correctly, and our important historical documents are very often kept in controlled environments. At greater risk are the writings and books of more recent years. Between 1850 and 1990, books were printed on mass-produced paper with a high rosin or pine tar content, which is causing them to degrade ten-times faster than earlier material.2 These works could all be dust within 200 years, leaving a black hole in our cultural and historical memory if we do not act now. But on a cheerier note, for those who have moved over to e-readers, or those who have already set about slowing the release of VOCs in their collections, and who are craving the nostalgic aroma of dying paper, a range of ‘old book’ scented candles and perfumes are available online.
1. Schmidt CW. On the smell of old books. Analytical Chemistry 2009;81:8656.
2. Strlic M, et al. Material Degradomics: On the Smell of Old Books. Analytical Chemistry 2009;81:8617–8622.