Book excerpt: The volume presents the results of a four-year inter-institutional, interdisciplinary research initiative led and organized by the National Gallery of Art. Contributions by 47 leading photograph conservators, scientists, and historians provide detailed examinations of the chemical, material, and aesthetic qualities of this important class of rare, beautiful, and technically complex photographs. The volume will help those who care for photograph collections gain a thorough appreciation of the technical and aesthetic characteristics of platinum and palladium prints and scientific basis for their preservation.