Thats a different way that looks great . I had read years ago when in HO that fade was very hard to do after the model is painted , as Tom states as well . It said to add white to black or any other color before spraying it . The fade will then be there , and the weathering can begin . I had some great success with that method , though my weathering left a lot to be desired . I used that method , engine black , faded with white , then sprayed for the roof and under sill area on those W&LG doodle bugs . I have even gone so far fading that some of my steamers in HO were a touch too faded for my liking and had an almost grayish hue to them under certain lighting conditions . The truss bridges I converted to N and were also with that method .
