2LaneCruzer
Super Member
Back in the olden days when I was an apprentice painter, we used to use a solution of Oxalic Acid to make "new" Cedar privacy fencing match the much older, grey and weathered portions. In a few days or weeks, the "new" stuff looked like the old stuff. Oxalic Acid is a powerful oxidant; so I submit to you that the primary factor at work here is air oxidation.