Mark H. McCormick-Goodhart

The Allowable Temperature and Relative Humidity Range for the Safe Use and Storage of Photographic Materials

Conventional photographic materials typically make use of a gelatin binder in one or more coating layers. Although the final image may be formed by silver particles, organic dyes, or other inorganic components, gelatin has been the material of choice for more than a century to serve as the image binder. Additional gelatin layers are also frequently present. They function, for example, as anti-curl layers or overcoat layers which improve abrasion resistance andlor alter surface texture. The gelatin layers are adhered to a common support layer, and substrates made of acetate, polyester, glass, paper, or polyethylene resin coated paper have found widespread usage. The physical structure of the majority of twentieth century photographic films and prints can be understood by considering combinations of these basic material components. The environmental guidelines for safe use and storage of photographic materials presented in this paper are applicable to and inclusive of these common varieties of films and papers. Temperature and relative humidity recommendations for photographic materials should be cited with two purposes in mindsafe storage and safe use. Room temperature and moderate humidity ranges are more suited to the requirements of frequent access and comfortable use and display while low temperature storage is important, indeed necessary in most cases, to meet long-term preservation objectives. Only temperature and humidity levels that reasonably guarantee both chemical and physical safety can be allowed, and the materials must not be harmed by cyclical conditions which occur as they move between storage and use. Chemical stability is often determined by accelerated aging tests, and natural aging

INVESTIGATION INTO THE DETERIORATION OF PAINTINGS AND PHOTOGRAPHS USING COMPUTERIZED MODELING OF STRESS DEVELOPMENT

AbstractThe environmental effects of temperature and relative humidity on the mechanical response of paintings and photographs were examined using numerical methods and computer analysis. The basic mathematical approach is introduced that defines the material parameters necessary to conduct such an analysis. Methods of determining the material and dimensional properties of materials with comments on the effects of increasing measurement. accuracy are discussed. Using measured material properties for paintings and photographs, complete computer analyses were conducted that modeled the physical response to changing temperature and relative humidity. The calculated results were compared to experimental test specimens subjected to similar environmental variations.

A General Model Relating Externally Applied Forces to Environmentally Induced Stresses in Materials

The structural degradation effects of temperature (T) and relative humidity (RH) are important considerations in the setting and maintaining of museum environments. An approach to determining the acceptable values for this environment would be useful if a general model could be developed from simple physical (mechanical) measurements. In this article, a general model is developed in which the mechanical behavior of materials composing museum objects can be described using the easily determined parameters, stress development (force), environmental conditions, and dimensional change. -- AATA