What I use is, Sodium Hydroxide NaOH, we call it here (Soda Cáustica). IMO 8 UN 1824 (these are family or number given by IMO and the UN for transportation matters, but could help you find a producer or stockpiler. It is very cheap, have to use in a tupperware like container, it will etch metal, specially alluminum, put about two litres of water and 250 grams of the NaOH, if the water is warm it will act faster. it is a very agressive stuff, so be carefull, with your eyes, clothes, use rubber gloves, and take any precaution like if you are working with acid. if the paint is not removed completelly repeat, use a soft brush, even a toothbrush, and rinse fully.