I admit to know hardly anything about finishing wood. I have made some crosses out of 3/4" Baltic Birch and was wanting to stain them with dark walnut stain. (oil based). It looked terrible, with blotches and areas that hardly stained and areas that were too dark. I thought I had read where you should sand and seal the wood before staining. I use a spray shellac and a polyurathane spray for finishing. Should I spray a light coat of shellac before staining? I usually just finish with lemon oil and shellac, but a customer wants them stained with walnut. HELP PLEASE!