Washington, Nov 11 'Don't judge a book by its cover' goes the old adage, but a group of scientists has given the metaphorical phrase a new twist after finding a method that tells an old book's condition by its odour.

The researchers have developed a test that can measure the degradation of old books and precious historical documents on the basis of their aroma.

They have claimed that the non-destructive "sniff" test could help libraries and museums preserve a range of prized paper-based objects, some of which are degrading rapidly due to advancing age.

Matija Strlic and colleagues have said that the well-known musty smell of an old book, as readers leaf through the pages, is the result of hundreds of so-called volatile organic compounds (VOCs) released into the air from the paper.

"The aroma of an old book is familiar to every user of a traditional library. 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 a part of the book as its contents. It is the result of the several hundred VOCs off-gassing from paper and the object in general. The particular blend of compounds is a result of a network of degradation pathways and is dependent on the original composition of the object including paper substrate, applied media, and binding," noted the report.

The researchers said that those substances hold clues to the paper's condition.

Conventional methods for analysing library and archival materials involve removing samples of the document and then testing them with traditional laboratory equipment, but the approach involves damage to the document.

The new technique - an approach called "material degradomics" - analyses the gases emitted by old books and documents without altering the documents themselves.

The scientists used it to "sniff" 72 historical papers from the 19th and 20th centuries.

Some of the papers contained rosin (pine tar) and wood fibre, which are the most rapidly degrading types of paper found in old books.

The scientists identified 15 VOCs that seem good candidates as markers to track the degradation of paper in order to optimise their preservation.

They added that the method could also help preserve other historic artifacts,.

The study has been published in the American Chemical Society's Analytical Chemistry. (ANI)