Piranha solution. There are old chemist's tales where organic residues don't flinge even after coming into contact with concentrated chromic acid for an extended period of time. For when that happens there's only one thing to turn to... piranha solution.
And there's an even more legendary tale that when piranha solution doesn't work, polymerists come by at night and steal your resin and notes.
Piranha solution consists of concentrated sulphuric acid (96% at least) and hydrogen peroxide. Oxidising, hydroxilating, peroxidating and protonating agents all in one. Everything looks black because everything was oxidised to carbon due to the oxidative power of hydrogen peroxide and the sulphonating and protonating power of the sulphuric acid.