Lots of burnishing, oiling and sprinkle fine floor sweepings, wood ash, cement dust to the oil, then rubbing back. Layer and layer of finish, allowing it to dry between coats. Color the oil to change the tone.
Light denting of the surface is very effective, chain rattled over cloth on the gun, tapping with rocks, then more burnish, finish more dirt, more burnish.
You are building up a finish in several months that might take years to develop naturally.
