gather materials
you will need: 9V batteries (1 to 13), alligator cables (2 to 14), a titanium item, baking soda, water (distilled, if possible), protective gloves (optional for lower voltages), aluminum foil, a small piece of cloth, a twist tie, a small bowl, a spoon, isopropyl alcohol (optional)

construct the "brush"
wrap one alligator cable end in alumnium foil, then secure a small piece of cloth over it with a twist tie

clean the titanium (optional)
put on your protective gloves and use isopropyl alcohol to clean the titanium. hand oils and other contaminants can affect the outcome of the colors

set up the circuit
lay out your batteries in a line so that you can connect the positive terminal of one battery to the negative terminal of the next battery. attach the brush to the last negative terminal and attach the last positive terminal to the titanium piece. chain the rest of the batteries negative to positive so they make a series

prepare the solution
add a bit of baking soda to water. not much is needed, it should dissolve easily

paint some color!
dip the cloth end of the brush into baking soda solution and brush the wet cloth over the titanium. re-wet the brush as needed - it's the liquid that does the anodizing. make sure that the brush does not contact the cable attached to the titanium or else you will short the circuit