Choose the area you want to paint - around a door frame, or along the top of the wainscotting - and decide on a design.
Mark your border, if you wish. Use a yardstick or tape measure to mark the desired height. Then use a yardstick and chalk to join the marks to create a faint, easily removable line that runs all the way across the wall or around the room.
Cut off and discard 1/3 of a potato with one clean cut.
Rinse the flat surface of the potato and dry it on a paper towel.
Use a felt-tip pen to sketch your design on the flat surface.
Score about 1/2-inch deep along the lines and carefully cut away or scoop out the unwanted part.
Rinse and dry.
Pour a small amount of paint onto a smooth, flat surface such as a glass pie plate.
Stamp the potato gently onto the paint; then stamp it on the wall.
Use a ruler, held above or below so you don't smear the paint, to find your next target and repeat the process.