During the 1980s, window films were superstars. They were applied to room-side glass surfaces to block ultraviolet rays. This prevented fading and heat gain and made big window areas more energy-efficient. But over the years, some films discolor and others get scraped and damaged and need to be removed and/or replaced. To remove film, fill a spray bottle with 100-percent pure sudsy ammonia. Then spray it on the filmed side of the window; cover it immediately with plastic wrap. The glass should be cool or shaded when you do it. Wait 45 minutes, remove the wrap and use a razor blade scraper to undo the film. And that's the On The House tip for today.