Hello, I've get 9 new internal doors. All made from pippy oak and I need to varnish them. Before applying Johnson's Clear Varnish do I need to use knotting solution? I used it on on skirting boards prior to painting and it left a orange stain around the knots, I'm concerned the orange stain would shine through the varnish. Is there a brand or type of knotting solution that does not leave the stain. :s