For a varnish suitable for cork frames intended for indoors, there is nothing to equal spirit varnish, which consists of methylated spirit lpt., shellac 4oz., and resin 2oz.; it dries quickly and gives a glossy finish: a cheap quality will do. Apply in a warm room, and well stipple it in all crevices. Thin out with spirit for the first coating, but use it thicker for the second or finishing coat.