Denim would work. The oldtimers used burlap from feed bags. I used a kitchen scrubby-sponge saturated with the thin version of Corrosion-X until I found that Big 45 stuff. Still do use the sponge as a follow-up, but now have a can of G96.
Remembering that the stuff they used in "hot tank" parts cleaners in my youth had creasylic acid in it. Every automotive machine shop stank of the stuff, as did the machinists. But I do recall that an iron head soaked in the tank for a few hours had lost any rust it might have had, along with all the baked-on grime, when it came out. It must have been related to the original Gunk formula, because they hosed down the parts with water after the soaking. EPA would have a conniption fit today,