Digital Image Correlation to Determine Shape Deformation of Paper Based Collections Due to Relative Humidity and Temperature Variations (2015-2018)

IPI has received a grant from The National Endowment for the Humanities in support of Digital Image Correlation to Determine Shape Deformation of Paper Based Collections Due to Relative Humidity and Temperature Variation. This three year project will focus on defining the permissible limits of relative humidity for rare books and other library and archive materials that are critical resources for humanities research. Dr. Andrew Lerwill, Research Scientist at the Image Permanence Institute and a PhD physicist with prior experience in conservation science at the Tate Gallery and the Getty Conservation Institute, will lead the research project.

While the study of safe limits for relative humidity (RH) for fine and decorative arts has received considerable attention, the complex and diverse mechanical structures of bound volumes has not. Mechanical (physical) damage due to dryness or excessive dampness is the principal reason why rare book and special collection materials require controlled environmental conditions. For many years, recommendations for preservation have emphasized close control around a target of 45-55% RH. What is not well established, however, are the practical limits where irreversible damage actually takes place.

For a bound volume in leather or vellum, the exterior surface may absorb or desorb enough water to result in physical harm in less time than is required for full moisture equilibration throughout the object. Understanding movements of the ‘skin’ of books in changing RH conditions has not been studied and will prove valuable in two ways—to help avoid damage to significant collections and increase their useful life, and to inform sustainable and efficient operation of HVAC systems in institutions that hold important humanities collections.

To overcome the difficulty of studying the mechanical behavior of complex book structures, IPI will employ Digital Image Correlation (DIC), a technology that is being used both in industry and the arts to dynamically assess expansion and contraction of composite objects. DIC is a sophisticated type of photogrammetry (measurement using images) that is very sensitive to movement in three dimensions. The experiments in this project will use both sheets of material and complete books. They will have an applied pattern of dots on their surface from which the DIC analysis will very accurately detect and describe movement when exposed to varying RH conditions and temperatures. At some point the dots will not return to their original position when the starting RH and temperature are restored. This will define when the damage is irreversible.

The results of this research will be presented in technical papers and conference presentations and will be incorporated into the analysis algorithms used by IPI’s environmental management software, which is currently used by more than 800 institutions worldwide.