In this work, surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy show that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays. The experimental behaviour of these electrode arrays fits very well with the numerical solution using optimal quasi-conformal mappings proposed recently by Amatore and co-workers [C. Amatore, A. Oleinick, I. Svir, J. Electroanal. Chem. 597 (2006) 69; C. Amatore, A. Oleinick, I. Svir, J. Electroanal. Chem. 597 (2006) 77]. The possible reasons for the formation of conical recesses are discussed.