Detail shots of the CSX GEs.  The process was acrylic, decals, and an oil wash, followed by powdered pigment.  A final coat of Dullcote sealed it all.

As pigment is intense and unforgiving, I use a small, stiff brush to apply the black soot to the air intake and roof areas.  Very light brush strokes from a fluffy make-up blends it.  I then rub a paper towel over the grate areas to allow the top details to pop out.

These photos are were shot on a white back drop in bright sun light so the contrast makes the effect less subtle than it is.