Stains on parchment may be eliminated by vacuum table application of different oxidants in areas containing no written text. If metallic ions are present, such as Fe²+ or Cu²+, even as traces, hydrogen peroxide may cause collagen depolymerization by mechanisms involving radical reactions. Attempts at inhibition based on the use of complexing agents for metals or free radical inhibitors were undertaken. The use of EDTA before and during bleaching could constitute a possible preventive measure. Light aging experiments show that deterioration after treatment is possible; results need verification.