Hi Rolf,
Wade's method seems reasonable for bone or leather, it will likely smell really bad however, as it roasts. Here is another formula right out of "Espingarda Perfeyta", a gunsmith's manual published in 1713 by 3 Portuguese brothers"
"In order to temper iron, however soft it may be, so that it may become hard as steel itself, the most common and easy secret that there is, is to roast some ox-hooves on the fire, without their taking light, and when they are cold to hammer them, and add to them as much salt, and one part of chimney soot. All must be well crushed and put together in a vessel, (do this next part after a few beers) and then on this is poured enough urine in order to incorporate all of it. And let this advice be taken, that the older this mixture be the greater is its force and activity (yeehaw)."
dave