Weathering with brushed oils is the time-honored method of doing so. Paul Jansen, who pioneered and popularized "weathering" and "aging" in the late '50s and '60s used oils (white, black, burnt sienna, burnt umber, etc.), turps, and the Pactra flat enamels available at that time. I copied his methods during the same period, and I can attest that the effects have stood up very well with interval time and wear.
These days, I am much more comfortable using a combination of Mont Switzer's use of Floquil washes, followed by judicious applications of Bragdon powders.
Denny
Denny S. Anspach, MD
Okoboji, Iowa