The Schaffitzel's had a leaky gutter right above this window. So water is dripping every couple of seconds, 24/7. The water hits the stone below the window and then splashes up onto the glass above, leaving mineral deposits on the glass. The result was very severe staining. The stains buildup was so bad, there was literally "flakes" of minerals on the glass (bottom right hand corner). Typically stains will polish right out, but this one was so severe I actually had to sand down the stain till I reached the surface of the glass. Check out these pictures!