Weathering 1989 Batwing

First, here is a working link.

http://darksidetoy.com/Batwing-Prop-Replica-by-Hollywood-Collectors-Gallery-and-Toynami

The fading/blending effect can be done with an airbrush. Each panel can be masked off and the lighter color faded in with the airbrush at an angle to the surface. Do a search for "airbrush fading" or "airbrush blending."

Will do - thanks  

You can also do it with pastel chalks if you don't have an airbrush. Lay a piece of tape on the panle line. Take a white, light grey, ect. stick and scrape with your knife to make a powder. Take a short flat brush and brush the powder from the tape back onto the exposed panel. Peel the tape off and you will have the effect your looking for. Seal the powder with a semi gloss topcoat.

You can see the same effect I applied to this Cylon Raider on some of the panels.