The size, weight, and shape of wedges, and the material from which they are made vary with their intended use and the preferences of the individual. A softer (more carbon removed) wedge will certainly be more pliable than a hardened one.Which will require more frequent maintenance but with minimum effort with a file. And since its already soft you need not worry too much if you cheat and use a grinder. If unchecked you will get frequent shrapnel. But a hardened tool when pushed past its integrity, look out. You will swear you were shot by a 357 Mag and will repeatedly check for an entrance and exit wound. The soft type of wedge is not intended to move / lift / pry extreme forces (this is where your mentioned old hardened wedges come into play). Use the shortest wedge possible that will accomplish your purpose. Hit the head squarely. Wedges should not be driven so tightly into the wood that blows deform the head of the wedge. Try to aquire an assortment of wedges and try them out. You will quickly figure out each ones advantage and unlock age old knowledge of mechanical advantage of one of the oldest simple machines. Hope i helped somewhat. But definitely don't try to temper a soft wedge and harden it. Just get the right one
