It was the midst of the cold war, and state censors had banned western music, and even some Russian music was deemed "dangerous". But ingenious music lovers found a way to listen to the forbidden music, recording it onto old x-rays. It became known as bone music.
Stephan Coates, the lead singer of British band The Real Tuesday Weld, discovered the clandestine recordings several years ago when he was on tour in St Petersburg.
He was so fascinated, he made a documentary and wrote a book: X-Ray audio: the strange story of soviet music on the bone.