Method for creating a spark across a spark gap

Method for creating a spark across a spark gap for igniting a flammable liquid to measure its flash point, by means of a spark generator which comprises an ignition transformer, wherein the spark generator, on a primary side of the ignition transformer, comprises at least one DC voltage source and, on a secondary side of the ignition transformer, comprises two electrodes delimiting the spark gap to be formed, wherein voltage pulses from the at least one DC voltage source are applied to the ignition transformer on the primary side thereof, which voltage pulses generate ignition voltage pulses on the secondary side, characterized in that the ignition transformer is operated in a first phase according to the flyback converter principle and in a subsequent second phase according to the forward converter principle and that successive voltage pulses of the same polarity are applied to the ignition transformer in the first phase and that successive voltage pulses of alternating polarity are applied to the ignition transformer in the second phase.