if it is fairly cleanish you can always strip all the old wax out of the frames and boil it up in a outside area the wax will float of the top when its melted,
but you never want to use old wax from an unknown source in your own hives as its asking for trouble
we use old wax that has been stripped out for the wife to make candles with and as for the rest the blow torch and soda crystals is best