I am trying to figure out how to harden leather for the accordian section of antique fireplace bellows. Traditionally the leather in this section is hardened or dried to the point, that when you flick you finger on an edge it sound and feels like paper. Very tight feel to it like a drum. I am new to leatherworking for man who used to do this has recently died and I have been ask to try to figure out to do this. i have boiled the leather for 10 mins. but it did not harden enough. Can any one give me any suggestions how to get the desired results? It would be greatly appreciated. thank you, chris