Removing varnish stains from glass, such as windows, requires weakening the substance for successful extraction. After varnish dries on a surface it hardens, making it difficult to remove without a softening agent. Once pliable, the varnish needs to be scraped to get the bulk of it from the glass surface. Using the proper tools and procedures ensures that varnish gets removed from the glass without the glass getting scratched in the process.
Pour 3 to 4 tbsp rubbing alcohol onto a rag. Saturate the varnish on the glass with the alcohol. Allow the rubbing alcohol to remain on the varnish for 10 to 15 minutes to soften the substance. If the varnish remains hard, apply additional rubbing alcohol and wait another 15 minutes.
Sprinkle 1/8 cup of water onto the area. Position a scraper with a thin metal blade at the edge of the varnish. Keep the blade flush with the glass to avoid digging into the surface and leaving scratches.
Scrape the softened varnish from the glass, in one direction only. Remove as much of the varnish as possible with the scraper. Add additional water if needed to keep the glass lubricated against the metal scraper.
Wet the remaining varnish residue with 1 tbsp baby or mineral oil. Add 2 tbsp baking powder to the oil. Scrub the area with a nylon scrubber. The oil loosens the varnish, and the baking soda provides enough agitation to release the substance from the glass.
Wipe the remaining varnish, oil and baking soda from the glass with a damp sponge. Spray the area with a glass cleaner and wipe dry with a clean cloth.