A novel two-step metallization scheme for the formation of highly conductive “black” metal electrodes is presented and its underlying physics is investigated with electrical, morphological and optical characterization techniques. It is found that silver oxide microparticles converted to silver nanoparticles at a temperature as low as 150 °C just for 10 min in the course of the first metallization step. Although this first metallization step has a much shortened sintering time, it does not produce silver electrodes with high enough electrical conductivity. By performing the second metallization step with an aqueous ionic solution, however, the electrical conductivity of silver electrodes is found to be enhanced by six to seven orders of magnitude, approximately 1.0×10⁷ S/m, only in 10 sec. Moreover, the color of silver electrodes is blackened by a factor of 1.7. This rapid two-step metallization scheme is found more amenable to an open continuous roll-to-roll printing process and the resulting sheet resistance of a “black” transparent conductive film exhibits 0.9 Ω/□ with an optical transparency of 81%.