For the hobbyist/maker crowd.
Bare Pens are a great electronics prototyping tool for makers/hobbyists of all ages. Nontoxic and water-soluble, they can be used without gloves or mask. Once applied the paint dries quickly at room temperature and can be removed with soap and water. Paint is black in color and can be over-painted with any material compatible with a water-based paint.
Uses include drawing circuits, cold soldering, attaching components and many more
Can be used as a potentiometer
Makes a unique microcontoller interface with low voltage DC power sources