sci-fifan

Hey guys I need some advice....I'm an amateur model builder. I have clear blue and I want to paint CLEAR PLASTIC PARTS. the only problem is that when I mix the clear paint with thinners or water in the case of acrylic and I airbrush it onto the parts the paint withdraws from the sides. the specific part that I need to paint is CONVEX in shape. how do you airbrush clear plastic parts with clear paint so that everything is evenly coated?????