Pigment retraction and focusing effect
As water evaporates from the inks, the fluid remains at the nozzles because of the capillary suction. As water is removed from the ink feed channel, a liquid flow in the channel is established to replenish the loss, pushing more pigment particles to the nozzle. Normally, it would have caused the pigment particles to clump and the nozzle to be clogged. However if the solvent polarity and the pigment chemical modification is adjusted right, the pigment will start to retract from the nozzle, fighting the liquid flow, going ‘upstream’, similar to the salmon run in rivers, where the fish is going in masses against the flow, upstream. This will create an increased concentration of the pigment somewhere in the middle of the ink feed channel, aka ‘focusing effect’. In the end, this effect is beneficial, as the nozzle does not get clogged; it is a valuable tool in ink formulation.