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Premise:
I will be cutting 4 files using the same cutting technique and piece of steel cut into 10 inch segments.
The pieces of steel will have the scale removed and be baked in an oven at 500 degrees for one hour to help anneal the steel and make sure there are no soft spots artifacts from being heated while the surface has the mill scale removed.
File 1 : just cut no hardening.
File 2 : heated to cherry red and quenched in water
File 3 : Case hardening with horn and sea salt
File 4 : The full lard, goat and clay treatment
Testing:
Each of these files will be tested against the same piece of mild steel for ten strokes and results of damage on the file and cutting ability on the steel will be noted.
Documentation:
From a translation of Theophilus On Divers Art
Book 3 Chapter 17-21
"Chapter 18 The hardening of files
Burn the horn of an ox in in the fire and scrape it.
Mix it with a third part of salt and grind it vigorously.
Then put the file into the fire and when it is red-hot, sprinkle the composition of it on every side.
When the coals are strongly blazing, open them up and hastily blow all arounds so that the hardening does not diminish.
Immediately take out the file and quench it evenly in water.
Take it out and dry it a little over the fire. In this way harden all files made of steel.
Chapter 19 More on the Above
In the same way you will also make very small files--- square,round, half-round, three-cornered, and flat and thin. These are made from soft iron and you should harden them thus. When they have been cut with a hammer or a chisel or a small knife , smear them with old pig fat and wrap them around with leather strips cut from goat skin and bind them with linen thread. After this cover them individually with kneaded clay, leaving the tangs bare. When they are dried, put them into the fire, blow vigorously, and the goat skin will be burnt. Hastily extract them from the clay and quench them evenly in water. Then take them out an d dry them at the fire. "
File cuting Video
http://www.youtube.com/watch?v=7XBmJrhoK1g
Adam Coulson's fabulous site which inspired this project