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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.
Beginner
Overnight
Instructions
1
1
Read Bacon
Read Bacon
"This process should be carried on only long enough to char the leather until it can be crushed in the hand."
2
2
Cut the scrap
Cut the scrap
Collect heavy leather scrap: the pieces left when shoe soles and heels are punched out, or old leather belting that is worn out. Cut it into pieces 3 or 4 inches across.
Materials for this step:
Leather1 scrapTools needed:
Leather Knife3
3
Pack the boxes
Pack the boxes
Fill hardening boxes with the leather pieces and put the covers in place.
Tools needed:
Case-Hardening Box4
4
Char overnight
Char overnight
At the end of the day, when the furnace has been running for several hours, set the boxes in it and shut the fire off: the heat stored in the walls chars the contents. If the furnace walls are too light to hold enough heat, run the fire very low for a while, then shut it off. Leave the boxes in until morning.
Tools needed:
Muffle Furnace
Heat-Resistant Gloves5
5
Check the char
Check the char
Take the boxes out. The leather is done when it can be crushed in the hand. Do not overdo it: Bacon warns that leather is easily charred too much.
Tools needed:
Heat-Resistant Gloves6
6
History and honest limits
History and honest limits
Bacon writes that charred leather was dearer than charred bone and kept for the finer work, and that bought leather char should come only from trusted dealers, as some used any scrap leather they could get. He counts leather a safe carburizer for all steel under 1.25 per cent carbon.
He describes the boxes and furnace only as the hardening boxes and hardening furnace of the shop; the knife and furnace type are ours.
Tools Required
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