The phenomena occurring between the electrodes in electric discharge machining when manufacturing features on the micro-metre scale (µ-EDM) is not fully understood. Poor quantitative knowledge of the sources of variability affecting this process hinders the identification of its natural tolerance limits. Moreover, improvements in measuring systems contribute to the acquisition of new information that often conflicts with existent theoretical models of this process. The prime objective of this paper is to advance the experimental knowledge of µ-EDM by providing a measurement framework for the electrical discharges. The effects of the electrodes metallic materials (Ag, Ni, Ti, W) on the electrical measurements defined in the proposed framework are analysed. Linear mixed-effects models are fitted to the experimental data using the restricted maximum likelihood method (REML). The main conclusion drawn is that the discharge current and voltage as defined and measured in this framework do significantly depend on the electrode material even when keeping all the other machining conditions unchanged.This investigation was carried out while the authors were at the Manufacturing Engineering Centre of Cardiff University.