Mechanical Properties

A well-known attribute of albumen prints is the fine crack pattern formed in the albumen layer. In addition, albumen prints have a very strong tendency to curl (if left unmounted). These physical characteristics have been studied from the point of view of conservation treatment and to determine the underlying physical and mechanical properties that cause cracks and curl. Messier in 1991 and Messier and Vitale in 1993 documented albumen cracking in a series of micrographs made using the scanning electron microscope and the environmental scanning electron microscope. In 1994 Messier and Vitale described how water-based treatment of albumen prints increases overall cracking. Also in 1994, Vitale and Messier showed that the underlying cause of this cracking relates to the fact that dimensional changes inducted by wetting and drying exceed albumen's capacity of strain at normal drying rates. Baas, Foster and Trentelman in 1999 assessed the effects of various types of aqueous immersion finding that aqueous immersion followed by rapid drying with ethanol produced the most loss in gloss, implying the high rate of strain on the drying albumen causes it to exhibit more brittle behavior. Other articles presented below deal with the physical and mechanical properties of gelatin. In general albumen and gelatin exhibit analogous mechanical behavior, though gelatin has a much greater capacity for strain than albumen.