Pentel Ain Stein 2B 0.2 (Made in Japan, Pentel Co.Ltd.) pencil lead was positioned in a 1.6 mm diameter glass capillary and fixed in place by heating one end of the capillary with a Bunsen burner. A copper wire was inserted in the other end, glued together with the pencil by means of conductive silver glue (16062 Pelco conductive Silver Paint, Ted Pella), and additionally enclosed in hot glue to form a stable electrode connection. The electrodes were first polished on sand paper and later on a piece of copy paper.