Painted wood can be stained after taking a few measures to expose the viable wood. The most important step is to use paint stripper to reveal the natural wood underneath the paint.
Select a paint stripper based on the type of paint you are trying to strip. There are different paint strippers for oil-based, latex and acrylic paints. Once you choose the correct paint stripper, apply it with a brush to the surface you want to strip. The paint stripper has to sit for up to a couple of days to maximize its effectiveness. Once the paint is soft and spongy, remove it with a rag or a paint scraper. At this point, the natural wood is exposed and ready for sanding and staining.