The Effects of Relative Humidity on Some Physical Properties of Modern Vellum: Implications for the Optimum Relative Humidity for the Display and Storage of Parchment

Abstract

The effects of different relative humidities on some physical properties of three types of calfskin parchment (vellum) were investigated. Standard samples were subjected to (1) tensile fracture, and (2) measurement of the force that developed when the restrained samples were subjected to step decreases in relative humidity in the region between 60% and 11%. The results indicate that although no particular level of relative humidity can be excluded in general from consideration as a storage or display cohdition on the basis of tensile testing data alone, at 11% RH there is an adverse effect on some individual tensile properties. Relative humidities above 40% increase gelation and opportunities for biological growth. About 25% RH is the lowest level that can be tolerated without inducing large stresses in the material. Onfull consideration of these results, the physical chemistry and chemical reactivity of collagen, and the results of a recent study of the biodeterioration of parchment, a relative humidity of 30% seems optimum for such objects. At 30% RH, a cyclic variation of ± 5% can be permitted with minimal effects of swelling and shrinkage.