By Victoria Gill
Science reporter, BBC News
The test could help to preserve treasured books and documents
The key to preserving the old, degrading paper of treasured, ageing books is contained in the smell of their pages, say scientists.
Researchers report in the journal Analytical Chemistry that a new "sniff test" can measure degradation of old books and historical documents.
The test picks up and identifies the chemicals that the pages release as they degrade.
This could help libraries and museums preserve a range of precious books.
The test is based on detecting the levels of volatile organic compounds.
These are released by paper as it ages and produce the familiar "old book smell".
The international research team, led by Matija Strlic from University College London's Centre for Sustainable Heritage, describes that smell as "a combination of grassy notes with a tang of acids and a hint of vanilla over an underlying mustiness".
"This unmistakable smell is as much part of the book as its contents," they wrote in the journal article.
Dr Strlic told BBC News that the idea for new test came from observing museum conservators as they worked.
"I often noticed that conservators smelled paper during their assessment," he recalled.
"I thought, if there was a way we could smell paper and tell how degraded it is from the compounds it emits, that would be great."
The test does just that. It pinpoints ingredients contained within the blend of volatile compounds emanating from the paper.
That mixture, the researchers say, "is dependent on the original composition of the... paper substrate, applied media, and binding".
Their new method is called "material degradomics". The scientists are able to use it to find what chemicals books release, without damaging the paper.
It involves an analytical technique called gas chromatography-mass spectrometry. This simply "sniffs" the paper and separates out the different compounds.
The team tested 72 historical papers from the 19th and 20th centuries - some of which they bought on eBay - and identified 15 compounds that were "reliable markers" of degradation.
"The aroma is made up of hundreds of compounds, but these 15 contain most of the information that we need," said Dr Strlic.
Measuring the levels of these individual compounds made it possible to produce a "fingerprint" of each document's condition.
Such a thorough chemical understanding of the state of a book will help museums and libraries to identify the books and documents most in need of protection from further degradation.
The information could also be used to fine-tune preservation techniques.
The method, the researchers say, is not exclusively applicable to books, and could be used on other historical artefacts.