Abstract: Methods and apparatus are provided for preventing clogging in impulse inkjet printers. It has been found in accordance with the invention that ink clogging during quiescent periods can be prevented by providing an ink that has the property of forming a barrier of higher viscosity ink where the ink contacts the ambient air. As a result, the viscous barrier shields the remaining ink from the effects of air exposure during the quiescent period. Thereafter, the barrier is removed by a series of sub-pulses that re-homogenize the viscosity barrier and clear the nozzle.