Tung oil is a natural substance extracted from the Tung tree. In the early 1900s, it was a popular floor wax before the advent of polyurethane and other more durable floor finishes. When tung oil dries, it develops a hard, semi-waterproof surface that must be dissolved in order to remove. Removing tung oil from a glass surface can easily be done using a chemical solvent, such as paint thinner, to soften the tung oil.
Pour 1 to 2 cups of paint thinner onto a cloth until the cloth is soaked. Lay the soaked cloth on top of the glass stained with tung oil. If the surface is vertical, simply dab the paint thinner onto the tung oil stain.
Allow the paint thinner to sit on the stain for five to ten minutes to soften the tung oil.
Wipe the surface of the glass with the cloth soaked in paint thinner to remove the tung oil. You will need to apply a bit of pressure to the rag to get the oil off.
Wipe the surface of the glass with a clean cloth soaked in water to remove all traces of the paint thinner from the glass surface.
It's a good idea to wear gloves while cleaning, since the paint thinner can irritate the skin. Small amounts of tung oil can be scraped off gently using a sharp razor blade. Try not to get the paint thinner too close to the edge of the window as it will dissolve the paint on the widow frame.