Rinsing with cold water alone does not harm a piston pen; unscrewing the nib unit is unproblematic on the newer model. On old Pelikan models like 100 and 100N, the mechanism should only be sparingly disassembled, since the celluloid barrel thread tears easily; celluloid can be repaired but only by few specialists. Ammonia and alcohol must be kept away from the material and should not be used. Pigmented inks like Parker Penman are critical because they can bake the piston during long inactivity; before each writing pause of one to two weeks, cleaning is sensible. For care of the piston seal, a thin silicone film is recommended, but only a non-additionally-modified silicone.