Unlike other types of window frames, such as plastic and steel, removing paint from aluminum window frames has to be done very carefully. Due to the delicate nature of aluminum, many traditional paint thinners will break down the metal in the window frame causing permanent damage. The best way to remove paint from an aluminum window frame is with aircraft-quality paint thinner--available at most auto parts stores.
Use a paintbrush to apply paint thinner to your aluminum window frame.
Use a metal scrubbing pad to rub paint thinner into the window frame and scrub off the paint. Wear gloves to prevent harming your skin with the chemicals in the paint thinner.
Rinse off the paint thinner using water.
Repeat Steps 1 through 3 until all of the paint has been removed from the window frame.