I'm with Drak, shellac is a great seal coat, easy to work with, and almost anything will stick to it. Zinsser has developed a universal sanding sealer called SealCoat, that I'm planning on using as a sanding sealer/basecoat on my next transparent finish. It's a pre-mixed dewaxed 2 lb cut with extended shelf-life, and it's "guaranteed to be compatible with oil-base polyurethanes, acrylic finishes, lacquers, catalyzed finishes and varnishes.". Lots of people still mix their own, nothing wrong with that, just don't keep it more than about 6 weeks after it's mixed. I don't french polish, but I've sprayed and brushed gallons of shellac on children's furniture, and it's both easy and fairly forgiving.