1. A method of detecting the presence of a first metal inserted into a second metal comprising the steps of: measuring a second metal baseline object using resonant ultrasound spectroscopy; measuring an unknown object having similar dimensions, and density as the baseline object using resonant ultrasound spectroscopy; comparing the baseline object and unknown object resonant ultrasonic spectra to determine if the unknown object has essentially the same resonance structure as the baseline object; and detecting the presence of the first metal in the unknown object by observing differences in the resonant ultrasound spectra, solely due to elastic property differences in the baseline object and the unknown object.