Pennies - 1 cup vinegar (Either white or apple. Apple produces a little more of a teal color rather than bright blue.) - cup hydrogen peroxide - 40 ish pennies (this number varies largely on the amount of tint you want to your vinegar.
Draw a circle with a square - Tack two nails to set the diameter you want, then rotate a framing square against the nails while you hold a pencil in the corner of the square. Rub a little wax on the square so it slides easily.