Use diodes! Unless I've missed something earlier in the thread, quenching diodes will
solve any sparking problems. In early days, rectifiers were either in vac. tubes or
made up of stacked plates of Selenium, far from practicality or perfection. Cathode to positive
shunting the coil. Back emf on open circuit is entirely carried through the coil. Schottky
diodes have lower voltage drop than Silicon, and fast-recovery diodes have speed advantages.