Precious metal objects have long been revered and passed down from generation to generation. The value of these pieces is intimately bound to the hallmarks or maker’s marks that are stamped or engraved into the pieces.
The aesthetic appeal of silver necessitates its polishing to remove unsightly tarnish. The more times it is polished, the quicker the hallmarks disappear. When the hallmark is completely gone, we have lost vital information about the piece including who made it, when and where it was made, and the history of the silversmith.
Museum conservator Paul Benson got the idea of trying to recover worn-off hallmarks after writing his dissertation on the possible applications of acoustic imaging in conservation work.
To test his theory, Benson had a few pieces of silver punched by local silversmith, Jordis Ver Lee. Then the hallmarks were slowly polished off to simulate what would happen over time to a piece of silver that is polished frequently.
Using a scanning acoustic microscope, the test pieces were examined. Even though the hallmark is not visible to the human eye, the metal retains the impression of the stamp.The microscope sends sound waves into the areas of compressed metal. The waves that reflect back from the stamp are captured by the acoustic lens to produce images of deformations in the stamped surface.
Using the acoustic scanning process, the recovery of polished or worn-off hallmarks can allow curators, scholars, collectors, educators and dealers unlock the mysteries of a piece’s past.
The Nelson-Atkins would like to thank Dr. Robert Gilmore at General Electric Research and Development for the use of equipment and assistance on this project. Funding was provided by a grant from the National Center for Preservation Technology and Training.