The ignition of electrical discharges in the dirty liquid filled gap, when applying EDM, is mostly interpreted identical as found in the physical research of discharges in air (Lichtenberg Figures) or in vacuum (Radio Tubes) as well as with investigations on the breakthrough strength of insulating hydrocarbon liquids. The servo controlled variable gap in real ED-Machining however differs very much from such condition. The author stipulates ignition of electrical discharges by the evaporation of particle bridges in the gap through excessive current. The ignition spot in the process area is conditioned by the remaining particles, removed from the electrodes, as well as gas bubbles from former discharges. The material removal procedure is grouped in an evaporation phase at start of ignition and later in the ejection of fused material by instantaneous boiling at the discharge spots. The gap width should be measured during all investigations on discharge parameters, because it changes in dependence from stock removal rates, while servo controllers only stabilise the average process.