Got the idea from an old pslac newsletter (july 96) available here http://pslac.org/table_index_rawhide.htm .
Re-tempering is fairly easy, just apply heat evenly with a blowtorch about an inch back from the edge until the steel turns brown/purple (260 c), then put it in a bucket of cold water. I used a 7 inch diameter blade and made a "tradional" round knife as well.