Background: Vellum is a material used as a substrate for many rare materials found in libraries. Such materials include maps, deeds and historic bindings, which can have associated pigments, inks and paper text blocks. True vellum is an animal skin that has been altered through chemical and physical means to resist putrefacation. It may come from a range of animals, and it has traditionally been produced in different ways in various regions and eras. Such differences may result in disparate aging and reaction characteristics. (Note: The terms “vellum” and “parchment” often are used interchangeably; however the current investigation refers to vellum as would be used in limp-vellum and stiff-board vellum binding structures.)
But most importantly, vellum is extremely hygroscopic and may dimensionally deform rapidly, radically, and irreversibly in response to changes in relative humidity. For instance, a vellum map that is restrained by adhesion to a support or a vellum binding that wraps around a book board may shrink if exposed to too dry an environment, causing splitting or warping. In particular, storage of vellum-covered bindings can pose special challenges since optimal environmental conditions to preserve the paper text blocks is widely considered to be too dry for most vellum bindings. In addition, significant dimensional changes may occur in vellum bindings exposed to wide fluctuations in relative humidity, such as 25% and 60% RH.
Contributing Study:
Hansen, E. F., and H. Sobel. “Factors to be Considered in Determining the Optimum Relative Humidity for the Display and Storage of Parchment.” In Postprints of the Book and Paper Group Specialty Session, 29th Annual Meeting of the AIC, Albuquerque, 1991. Washington, D.C.: American Institute for Conservation, 1991.
Project Description: The overarching goal of the Library’s current project is to determine optimal storage conditions for vellum materials in order to keep distortion to a minimum, in particular without placing additional stress on auxiliary supports, especially binding structures. To do this, the Library will first conduct a series of controlled tests exposing various types of selected vellum substrate samples to changing RH at constant temperatures, noting any occurrence of planar distortion. Subsequent experiments will determine the effects of variables, such as boxing to protect samples from distortion in fluctuating conditions, and the effects of RH on different binding structures.
