When ink in a piston pen has dried out and the piston no longer moves, a simple water bath helps. Place the pen without cap with the nib pointing down into a glass and add lukewarm water (about 40 °C) so that the knob ends just under one centimetre above the water level. The pen should stand for at least three days, since the capillary forces of the feed slowly draw the water into the reservoir; turning the pen over once a day so the water also reaches the piston is sensible. This method works reliably but requires patience. A faster alternative is to unscrew the cone from the barrel with a special wrench and clean the barrel directly, which takes about an hour.