Hi. I've been having an issue with removing old paint from steel door frames. I've gotten the decades of paint off with various paint removers. But it's the bottom layer that refuses to come off! It's a ruddy colored, splotchy layer that can't be sc****d off along with the other layers. So far I've had success only by aggressively using the brush dipped in paint remover, rubbing with wet steel wool, and wiping off with a wet sponge. Repeat 2-3 times. I've tried wiping down with mineral spirits and paper towels with no success. I wouldn't mind the process if I didn't have 12 other door frames to strip! Does anyone know what this layer is? Or have another suggestion to get it off? Help please!