A typical home-made wiping varnish will use one part drying oil such as boiled linseed oil, one part of some sort of resin based finish like polyurethane, and one part thinner, either mineral spirits or turpentine. To my knowledge, denatured alcohol would not be appropriate as it is not a thinner for either the oil or the varnish. Denatured alcohol is usually the thinner/cleaner/base for shellac.
Best,
Tom