"Sweating" film from the glass is a fairly easy process. This technique involves using a black trash bag to absorb heat from the sun, plus soapy water or a 50% ammonia and 50% water mix, to soften up the adhesive.
The tools required for this method are very common. Other than the warm sunshine, you'll need a sprayer. Fill the sprayer with half water and half ammonia. This can be substituted with other products such as Windex and foaming glass cleaner. Also, citric acid based cleaners work and smell better. You'll also need large black trash bags. Cut them open to cover as much glass surface as possible. Use a scraper if you prefer, like the 6 inch MK-2 scraper or the 4 inch heavy-duty scraper with long handle, along with plenty of new replacement blades. Finally, you'll need a scrub pad, paper towels and a cleaning squeegee.
After preparing your work area by removing any blinds, curtains, etc... lay down your drop cloth and make sure any tools needed are close at hand.
Preparing the bag
Step 2 cover the
whole surface
Step 4 wait for surface to warm
Generously spray the window with your preferred solution.
Take your black trash bag and hang it on the window covering the whole surface of glass.
Spray the black trash bag with solution and smooth out any air pockets. Make sure the bag is lying directly on the film.
Wait for the window surface to warm so that it is almost too hot to touch. The average waiting time is between 40 minutes to an hour.
Once the window is ready, start from one of the top corners and slowly lift the bag, with the film attached, from the window. Be sure the bag stays against the film surface.
If the bag comes off the film more than two or three inches, the moisture might evaporate too quickly, jeopardizing your film removal.
Once all of the film is off the glass, re-wet the window and scrape it with your desired scraper. Work from the top down and keep the glass wet.
Inspect the entire glass surface for any film or adhesive left behind. If any is found, spray the area with solution and scrape it clean.
Spray the window once more and complete final cleaning. Squeegee out while drying your blade after each stroke.
Note: when working with dual pane windows, sweating off old film can cause thermal stress fracture on the window or blow out a seal.