Man I just went and picked all my RC stuff up from my sisters house the other day. I need to get a workbench set up in the man cave to get them all going again.
We used to do that with ear defenders and black shoe polish. Or with the headset you connect to an aircraft to communicate with the pilot. We would normally clue the pilot in so he would be telling the person wearing the headset he was having a hard time hearing them and to make the mouthpiece tighter. On a good hot day the shoe polish would start dripping down their head or face pretty quickly.