Randy,
while not an expert ,, some experimentation has been done in my "studio" lol,
One method , essentially a modification of Shultzie's description, that I have used. I gathered a stack of exposed xray film from a lab one time. its thin, rigid and easily cut. I cut the star shape I wanted into the film, then holding it just over the surface of the model, spray lightly, more air than paint but low pressure. Then you can make one more intense blast at the center of the mask film making the burst in the center. still takes a steady hand, and some practice, but I liked it better than a mask that was stuck flush on the surface.
as for shading canopies, I have started with a black base, then using pearl in clear, done my shading.
for the main body, I spray with a blue and red pearl mix, mostly blue as i recall. Then I add some green pearl to the mix, spraying lightly around the perimiter, this "greys" the color of the pearl slightly making a better shadow effect. Now one revision on this, you can use colors that "match" your color scheme instead of the blue ~ red combo. just remember that to make brown, or to make a color dirtier, a small amount of the remaining color will dirty it up. I have also added a drop of violet, or grey toner to the shading mix to get a bit more pronounced variation in the shadows..
I normally shade around the back edge, and the bottom edge of the canopy area. A sharper shadow on the back edge than the bottom edge seems to be more aesthetically correct to me for some reason, the sides get a nice gentle blending of shadow,,,