In your September column you were asked about a paint-over tracking system. By coincidence, I was recently reading about the radio frequency labels used for shoplifting control. There are several versions of these labels, some of which are quite thin and could be used for this type of application. As I recall, they can be encoded with various numbers, so they can be used for unique identification. I am not associated with these products, cannot help with actual names and don't remember where the article appeared. J.M.
I just told my wife, "The readers of Painting Clinic are the smartest people in the world." I knew that one of them would answer this difficult identification tracking question. Those radio frequency devices are detected even when hidden under several thick coats by shoplifters. Certainly similar devices will be detected under several thin coats of paint. Their real advantage is that they can be encoded with various numbers. Ah, the wonders of science!