I've always assumed it was an airbrush. In '72 there were some obvious ones.
That was the first year I collected cards (I had a few from '70, including Bench), and that year's series still sticks in my mind.
Edge trilogy, by me.
Go to the edge of the cliff and jump off. Build your wings on the way down. --Ray Bradbury
What begins at the water shall end there, and what ends there shall once more begin. --Straka