One of the keys here is to use a wire brush and lightly go over the charred area. This knocks loose any ash. Personally, I would seal the piece with Shellac. Brush it on at a 1 pound cut and let it dry a few minutes. Go back over it with some 000 steel wool or pad. Remove the dust and top it with some 2 pound shellac to build a film coat. It can be done in an afternoon.