Wayne,
I believe John Jordan uses a Japanese Automach reciprocating carving tool with a nail that has been ground round on the end. I do this also. Any reciprocating carver will work. Some also use a rust scaler, put the impact area is much larger with all the needles compared to just one when using the carver, it presents other issues. Betty Scarpino has used an engraver to achieve a similar texture. In each of these cases, a fine wire brush and 3M spiral disk clean up of the surface works real well. You will need to practice on scrap wood until you get a feel for the technique.