During the 1980s, window films were superstars, applied to room-side glass surfaces to block ultraviolet rays, to prevent fading and heat gain and to make big-window areas more energy-efficient. But over the years, some films discolored, others got scraped and damaged and now need to be removed or replaced. First 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, then remove the wrap and use a razor-blade scraper to remove the film. And that's the On The House tip for today.