Seventeen out of 21 obliterated stamped serial numbers on test specimens of copper, brass, steel, and aluminum were successfully restored. Cavitation induced in water by a piezoelectric transducer was the mechanism used. Primarily, smeared metal was removed from the number grooves by the force of the cavitation, however, numbers were also restored at depths at or below the level of the stamped grooves.
SUMMARYThe identification characters, SRI 8368, were stamped on specimens of copper, brass, steel, and aluminum, and then partially obliterated by grinding at the Stanford Research Institute, These specimens were then submitted to the NASA Lewis Research Center for studies of the effects of a new restoration technique. The restoration mechanism was cavitation in water induced by the ultrasonic vibration of a piezoelectric transducer. All the stamped numbers and letters were completely or partially restored on specimens of copper, brass, and steel.. Two out of five of the original numbers were restored on aluminum,, (The aluminum specimen was originally used for optimizing variables in the restoration process. These variables were separation distance between specimen and vibrator, vibrator power, amplitude, and test time. Temperature and frequency were held constant,) On the copper specimen smeared metal was removed from the number grooves by cavitation. On brass all the numbers appeared in the form of a lightreflecting haze that was slightly brighter than the cavitation damaged background. This was unexpected because the measured depth of grinding was deepest in this specimen -about the same as the depth of the stamped numbers. In steel smeared metal was removed from the number grooves; however, one deeply ground number was restored in a manner similar to the numbers on the brass specimen. In aluminum, letters outside the region being attacked by concentrated cavitation were restored, but not those within the region, indicating that the first attempts of number restoration on this specimen were too severe. After standardized conditions were established, seven new numbers were 1 2 stamped on the aluminum, obliterated by grinding, and restored by this technique. Again, smeared metal was removed from the number grooves.The important conclusion herein, is that the feasibility of this restoration technique has been clearly demonstrated. The method is recommended for use in crime laboratories as a relatively low cost technique that can restore serial numbers on most materials with the minimum of preliminary surface preparation,
