Many years ago a old pipeline welder taught me how to caseharden with just a acetylene torch and water,interestingly its pretty much exact way folks have done it with storebought carbon in this thread, difference is rather then buy a can of something you just use carbon from straight acetyline flame, blacken the frizzen face pretty thick with soot,heat to cherry red,anouther layer of soot,hold at cherry red a few minutes drop in water,it takes a little practice to get hardness your after but it does work very well, I practiced with nails,#9 wire,or just small pieces of scrap steel to get decent at it