Silver objects in particular require polishing to maintain the lustrous metallic surface; hence hallmarks tend to be worn away over time resulting in the loss of important historical information.
Utilizing Scanning Acoustic Microscopy, an image of these vanished or illegible marks can be recovered. Two imaging modes are presented: time resolved surface wave imaging of the near surface deformation and direct reflection from the back surface through the remnant deformed metal. The contrast in these images is caused by variations in the ultrasonic velocities in the metal, density changes, and acoustic attenuation in the deformed metal microstructure.
This technique is non-destructive and non-contact. Images and discussion of experimental results are presented.
2004-02 Image Recovery of Worn-Off Hallmarks on Silver and Gold Objects
2004-05 Ultrasonic Non-Destructive Imaging of Worn-Off Hallmarks on Silver: Preliminary Results
2004-06 Non-Destructive Imaging of Worn-Off Hallmarks and Engravings from Metal Objects of Art Using Acoustic Microscopy
This research was made possible through Grant MT-2210-0-NC-21 from the National Center for Preservation Technology and Training (NCPTT).