Title: Innovative use of X-ray radiography in the study of daguerreotypes: identification of hallmarks

Abstract: X-ray radiography is an imaging technique widely used in the examination of works of art and heritage objects, however no references to its application to the study of daguerreotypes have been found. The results obtained in this study demonstrate for the first time the usefulness of X-ray radiography for locating, identifying, and characterizing the hallmarks on the daguerreotype plates. Hallmarks are of great importance for the knowledge of these photographic objects since they provide unique information for their dating. In this study five daguerreotypes were X-rayed using two different working procedures designed with the aim of recording the hallmarks, one by means of radiographic film and the other using a digital detector. The working procedures presented here not only enabled locating the hallmarks of all daguerreotypes studied, but also allowed its positive identification without extracting the daguerrean package or handling the plate, avoiding its exposure to damaging environmental factors. X-ray radiography is thus revealed as an innovative and easy to integrate tool for the study of daguerreotypes, both for the characterization of hallmarks on the plate and the analysis of other elements and manufacturing procedures.