Charred Leather: Shoe-Sole Scrap Charred in Hardening Boxes Overnight (Bacon, 1919)

Charred leather is packed round steel in a closed box to case-harden it; John Lord Bacon calls it the very best carburizer for fine work. His Forge-Practice and Heat Treatment of Steel (1919) has it made in the shop from heavy scrap: the pieces punched out when shoe soles and heels are cut, or worn-out leather belting. Cut into 3 or 4 inch pieces, the leather is packed into covered hardening boxes and left overnight in a hot furnace whose fire has been shut off, just until it can be crushed in the hand. Source: J. L. Bacon, Forge-Practice and Heat Treatment of Steel, 3rd ed. (1919), pp. 335-336. Picture: his p. 336.