Due to its capability of dispensing very small volumes of different liquids in a controlled manner, ink-jet printing is well suited for combinatorial experiments. The multi-nozzle ink-jet delivery system is especially advantageous for parallel chemical synthesis of different materials. We have used ink-jet printing of an oxidizing agent to pattern a pre-coated conducting polymer, poly(3,4-ethylenedioxy)thiophene-poly(styrene sulfonate) (PEDOT-PSS), yielding electrodes with predefined shapes and a controlled degree of sheet resistivity for use in gray-scale organic light-emitting devices (OLEDs). The electrical and optical properties of the PEDOT-PSS layer are modified via chemical interaction using the oxidizing agent. These experiments were performed using a desktop ink-jet printer in conjunction with common graphic software which employed color functions such as CMY (cyan, magenta and yellow), HSL (hue, saturation and luminosity) and RGB (red, green and blue).