Abstract: A free ink roller ball pen for dispensing low viscosity inks containing pigments that are prone to sedimentation. The instrument contains an ink reservoir chamber, a nib chamber provided with a roller ball socket assembly, a pressure equalization overflow chamber for the low viscosity ink, and a special agitation system for the ink reservoir and nib chamber. The agitation system comprises a weight, with a cross section smaller than the interior of the nib chamber, connected to a wire having a diameter smaller than the back inner diameter of the ball socket assembly. The length of the weight and its confinement are selected to provide for a predetermined stroke, on shaking the pen, that sweeps out the internal space of the nib and also the back of the roller ball assembly, to re-disperse any pigment that has precipitated.