Discharging a high-energy spark underwater creates a shock wave that dissipates through an acoustic field. The hydroxyl radicals created by the field are able to mildly oxidize the surfaces of ink and toner particles suspended in water, thereby decreasing their potential. This decrease inhibits the tendency of the particles to reattach to fiber, which is negatively charged. Pilot studies showed that sparking a slurry of recycled newspaper and magazine furnish decreased residual ink on fiber by 21%, increased brightness by 1%, and reduced fiber loss by 1% when the treated furnish was subsequently subjected to flotation deinking. No benefit was realized if the furnish was sparked during deinking, possibly because the shock wave changes the bubble-size distribution.