Polly Scale clear flat thinned 60:40 to 40:60 (depends what you prefer) with 45% isopropyl alcohol, shot from 6-8 inches at 35-45 psi (using a Paasche H, #1 tip) and misted on several very light coats works for me. I have yet to have a pastel be too accented with this method and a few tended to "disappear" a bit but you can give a quick swipe of fresh pastel between coats of flat.