Abstract: An electrolysis apparatus for coating a metal, typically aluminum, with an oxide, which applies long voltage pulses to the control electrodes of the thyristors 13, 14, 15, 16. The thyristors control the flow of alternating current between the metal sample 17 and the stainless steel electrolysis tank 18, which typically holds an alkaline water solution. An alternating voltage power source of about 350 volts rms is provided by the transformer 11, and current flow is regulated by the capacitor 12. The long voltage pulse is applied to the control electrode of each thyristor when the thyristor is back-biased and maintained until after it is forward-biased, thereby allowing the thyristor to turn on optimally without generating a current spike. Current spikes can degrade the oxide coating and cause electromagnetic interference.