Scanning droplet cell microscopy was used for patterning of anodic oxide lines on the surface of Al thin films by direct writing. The structural modifications of the written oxide lines as a function of the writing speed were studied by analyzing the relative error of the line widths. Sharper lines were obtained for writing speeds faster than 1 mm min(-1). An increase in sharpness was observed for higher writing speeds. A theoretical model based on the Faraday law is proposed to explain the constant anodisation current measured during the writing process and yielded a charge per volume of 13.4 kC cm(-3) for Al2O3. From calculated oxide film thicknesses the high field constant was found to be 24 nm V-1. Electrochemical impedance spectroscopy revealed an increase of the electrical permittivity up to epsilon = 12 with the decrease of the writing speed of the oxide line. Writing of anodic oxide lines was proven to be an important step in preparing capacitors and gate dielectrics in plastic electronics. (C) 2013 Elsevier Ltd. All rights reserved.