This is a great tutorial on weathering different types of material:
http://www.thedentedhelmet.com/f34/...-welcome-23363/?highlight=weathering+tutorial
My advice is to definitely follow one set pictures so that the weathering is consistent. I personally am a fan of more weathering, as it makes the costume look "lived in." Go slow, and in layers. You will find that when photographed, the flight suit will look different, so you may need to add more. Don't be afraid to get dirty, and use multiple mediums - acrylic, motor oil, spray paint, charcoal (go easy), heck....DIRT
Don't forget to do all sides, and underneath flaps and sleeves.
Avoid any 'harsh lines.' You want it to look natural. I've used very light sandpaper to blend in some of the lines, or dilute your medium with water and work it in with your hands.
Hope this helps.
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Can you guys point me to a few reference photos that best show which areas to mist more heavily? I'm definitely going after the grimy look but I don't want to mess the paint job
Think about areas on the flight suit that would get used a lot - pocket flaps, ankles, joints, seems...again, like I said, find a set of the same photos in the gallery and go from there!