The spark assisted chem. engraving (SACE) of glass has been investigated using current/voltage measurements combined with photographs of the tool electrode under different regimes. Depending on the applied potential, different domains have been identified. At low potentials (<10 V) a cone-shaped region contg. finely dispersed hydrogen gas is formed around the tool cathode. At high potentials (>25 V), there are strong current fluctuations mainly due to bubble coalescence. The authors speculate that in this regime, due to the Ohmic heating, the temp. in the vicinity of the tool electrode reaches the b.p. of the electrolyte resulting in the generation of water vapor bubbles. These bubbles cover the active surface area of the tool electrode, leading to blanketing (i.e., isolation between tool and electrolyte). Once the bubbles dislodge from the tool surface, contact between the electrolyte and tool is re-established and the cycle is repeated. This last region (>25 V) is the working domain of the SACE. Finally, some examples of glass machining are given to demonstrate the potential application of this technol. [on SciFinder (R)]