I'm refinishing some old cherry and mahogany windows. The rails and stiles have been scraped clean of the old paint and multiple layers of varnish. The surface is lightly sanded and the wood stained so all surfaces are similar in appearance. I was always taught to apply several coats of shellac to seal the surface and then to apply the spar varnish. Recently I was told the shellac was completely unnecessary and a waste of time. What does the thundering herd think? Shellac first or direct to varnish?