Oh, I thought you were using prismacolor colored pencils. You are using pastels? I have not used them in years although I love what I see from friends. I have never varnished over them. I did not realize that would take well. Are you using varnish like oil paint varnish and then acrylic paint? It sounds like an interesting process. I use the prismacolor colored pencils and paint over them with lighter fluid to blend.