Model predicts 'shelf life' for library and archival collections

Scientists at University College London (UCL) have developed demographic models of decay and loss to predict when a large library or archival collection might age beyond repair.

"Although some library materials might easily survive thousands of years some have internal clocks triggering faster decay. Using the demographic models we can now easily predict how much more degradation will be induced by a hotter and more humid climate in the future, and perhaps more importantly, how this can be mitigated," lead author professor Matija Strlic said.

The model developed by Strlic's team explores what makes an historical paper unfit for use, the degradation of historical documents due to handling, and how heritage resources can be managed and stored with more economical and environmental sustainability, according to a UCL statement.

The team developed an equation describing how the length of cellulose, the dominant macromolecule in paper, decreases with time depending on the acidity of paper and the environmental conditions during storage.

Another model described how wear and tear accumulates with instances of reading of a book or an archival folder.

The scientists looked at more than 600 historic documents from all over Europe to arrive at a general demographic model describing how ageing progresses and fitness is lost.

"We considered a heritage collection as a population of people and used census methods and ageing models to predict how a large library or archival collection might age beyond repair," Strlic said.

"In relation to the outcomes of the recent COP 21 climate change conference in Paris, the projected average increase of 2 degrees centigrade in the global climate will increase the rate of degradation of some heritage collections by around 50 percent, and a four degrees centigrade increase would halve their lifetime," the professor from the UCL Institute for Sustainable Heritage added.

"We can either pump more energy into indoor climate control, which is evidently unsustainable, or use our demographic models to improve collection conservation and reduce energy use at the same time."

In addition to looking at the wear and tear of historic paper the reports also looked at the public's perception of the documents' fitness for use.

The three part report on the model, 'Damage Function for Historic Paper', was published in the latest issue of Heritage Science.