Paint thinners are the easiest way to remove any type of paint. There are many different chemicals you can use as paint thinners. Some are natural and fairly harmless, but others are very caustic. The toxic fumes in paint thinners have been linked to damage to the nervous and reproductive systems. Always keep the area where you are using the thinner well ventilated, wear safety goggles and gloves, and make sure to dispose of all paint thinners safely.
Turpentine is a chemical usually derived from pine oil but sometimes manufactured from crude oil. It is most effective on oil- and alkyd-based paints. It will also clean dried-on paint. The naturally made version produces noxious fumes, and is being used less for that reason.
Mineral spirits are a petroleum-based product. They are best used on oil-based paints that are still fresh. Many artists and painters use them to clean brushes. They have less odor than turpentine but have their own dangerous fumes: methane produced by the hydrocarbons in the mineral spirits.
Methyl Ethyl Ketone (MEK)
Methyl Ethyl Ketone, or MEK, is a very caustic paint thinner that is man-made but also found in nature. MEK has been found to cause damage in the throat, nose and mouth if too much is inhaled. It is used to remove paint that has hardened on hardware such as hinges and door knobs. Test your MEK thinner on an out-of-view area before using it to remove paint.
Acetone is the least toxic and least aggressive paint thinner ingredient. It's used mostly by art restorers to remove dirt and grime from older paintings. Acetone is made naturally by the body, and has no adverse effects on people or the environment. It is, however, highly flammable and should be handled with care.