Download: 2004-04
Size: 1.3 MB
Hallmarks on silver and gold objects can reveal much about their history. The name of the
metalsmith, the date of manufacture, the quality of the metal alloy, and other pertinent
information can be determined from the study of the hallmarks. 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.