You can definitely sand the finish off the glass. Be careful once you reach the glass so as not to sand too much of the glass itself. You will know when you;ve reached it....both by how it looks...whitish...and how it feels under the sandpaper. As far as the oil goes...that may depend on the oil. I've used danish oil on cherrywood and clear coated with Minwax poly with great success. On oily woods, I will wipe it down with acetone to clear the oil from the surface and then clear coat with poly.