For me, one of the pleasures of old Flash Gordon serials is figuring out what the costumes and props were made from - the actual clothes look to have been pulled from stock - they're comic-opera European military uniforms, mostly. I was looking again at the helmets Ming's soldiers wear, and thinking "ok, the base is a leather football helmet - the vizzard is either a welder's mask, or a piece of cardboard cut to the shape of a welder's mask; oh, hey, I think those are mason jar lids on the ears."