Manganese-(III) species is generated and regenerated in a mixed aqueous acid solution containing manganese-(II) species by injecting ozone gas in the mixed aqueous acid solution such that ozone oxidizes at least some of the manganese-(II) species to the manganese-(III) species with at least 60% Mn(III) generation efficiency. The acids include sulfuric acid and an alkane sulfonic acid. The aqueous acid solution containing manganese-(III) and manganese-(II) species is used to etch polymer materials. The etch is a chrome-free etch method.