In magnetic recording tape, a solution of magnetic particles suspended in a binder.
"Thanks for all you did with the old vinyl record I sent in! You did a wonderful job with a record from 1944 sent home by my uncle when he was being deployed over seas for WWII. He never came home and this is the only recording of his voice we have. To be able to hear it on a cd player now is fantastic! thanks so much for all you did. great ..."