Thanks, Ernie and Andreas!
Ernie, the rib shading on the roundels is post-shading with pastels. Extreme care is a must here. First of all, I spray a couple coats of clear flat to reduce tape adhesion. Then I lay Aizu Micron tape lightly over the ribs. I don't really press the tape down as I would for other masking jobs. To avoid going overboard with the shading (not always successful), I use a small, soft, short bristle brush using very light strokes to apply the pastels, then a larger, stiff bristle brush to remove the excess and blend it. I then, very carefully and slowly, pull the tape back on itself and if all goes well, the decals remain unharmed. To finish it off, I brush one more time then seal it with a clear coat. Hope that's useful.
Cheers,
Bud