A potentiodynamic polarization technique was used to assess the quality of passivating overcoats on Si nozzle plates for continuous stream ink jet printing. These include Si3N4, SiO2, and SiC films deposited by various methods. The worst overcoats dissolved under an anodic potential. The others were electrochemically inert or nearly so. Even among these the protection provided differed widely. Overcoat rankings using the polarization technique compared favorably with microscopic examinations. The best was plasma-assisted CVD a-SiC:H from an SiH4-CH4 discharge. Some overcoats and combinations were pinhole free over the 1 cm2 tested. © 1982, The Electrochemical Society, Inc. All rights reserved.