Cracking in albumen photographs: an ESEM investigation.

The preservation of nineteenth-century albumen prints is of great concern to collection managers and to conservators of photographic materials. In the field of art conservation, preservation techniques incorporating aqueous treatments are often used to enhance the long- and short-term stability of historical artifacts or art objects. In a study of the interaction of water with albumen photographs, experiments were carried out in the ESEM to follow the real time effects of water on the prints. The experiments were designed to observe the effects of a range of relative humidities and liquid water on samples of expendable historic albumen prints, utilizing the advantages of imaging in the presence of water vapor. All albumen photographs exhibit a fine network of cracks in the albumen protein layer. Average crack with is approximately 10 microns. As observed in the ESEM, a 4.25-fold increase in the width of a single crack (at 50% RH), viewed normal to the surface, resulted from a single controlled excursion to high relative humidity and immersion. In an extraordinary series of images, a print viewed in cross-section exhibited a 22% swelling and shrinkage in thickness, and a 5% and 9% swelling and shrinkage along the width of a fragment of the albumen/image layer when the sample was immersed in water and dried. The visual information gained through the use of the ESEM helped to focus a materials investigation and served as a foundation for a study which shows that aqueous treatment causes increased cracking of both unsupported albumen and the albumen/image layer in prints.