Here is one of my officially-licensed Harley-Davidson reproductions. I painted the original on 24" x 36" paper. Much of the detail you see was first drawn with pencil. I then painted over the pencil with an airbrush using very transparent paint. If you are thinking that sounds time consuming, you're right ;-) It has been featured in numerous publications.
It is a Mixed Media on Paper at 24" x 36".