According to Ace Hardware.com, using chemical strippers to remove paint from metal is the easiest and fastest method. Usually called "paint strippers" or "paint removers", chemical strippers are available in paste, liquid and aerosol forms.
Pastes are used for fixtures that are located overhead, such as a chandelier hung from the ceiling, or on the wall, such as a light switch. Pastes can be applied in multiple layers to ensure the stripper will stay moist and work effectively on the paint; most of them are removed with water once the paint saturation process is complete.
Ideal for unusually shaped fixtures, liquids are most commonly used to remove thin layers of paint. If you have a difficult time keeping the liquid remover moist, cover or place the affected metal object with a plastic garbage bag secured with Scotch tape or a Ziploc bag.
Aerosols are the easiest and fastest method. Perfect for small jobs or detailed surfaces, these removers stay moist and can easily be reapplied until the paint is removed. Finish this process by rinsing the metal object with water.
Whichever method you use, always ensure the area is well ventilated to avoid inhaling chemical fumes. If necessary, use sandpaper, a paint scraper or steel wool to remove any final stubborn spots.
If you are having a difficult time removing the paint with chemical strippers, try sanding the metal object. Begin with 80-grit sandpaper. When the layers of paint are mostly removed, finish the removal process with 120-grit. If you are removing paint from a large metal object, consider using a power sander--belt, disc or drum sanders are all possibilities. Always wear a mask to avoid inhaling paint dust.
Heat guns or electric paint removers are a less common but very effective option. Both choices use heat to destroy the paint's film, making it possible to scrape the paint from the metal object immediately after heating. A propane torch is a more common household item that can be used to perform the same function. Whenever removing paint with heat, always wear a mask and ensure the area is well ventilated to avoid inhaling toxic paint fumes.
If the metal item is small--such as a doorknob, hinge or escutcheon plate--a long soak in the crockpot is an easy option. Simply place the item in the crockpot, cover with water, add 1/2 tablespoon detergent and turn the crockpot on high. Allow the item to soak for three or four hours, remove the item from the crockpot and try to rub the paint off. If the paint won't budge, replace the item in the crockpot for a longer soak.