Agriculture Reference
In-Depth Information
The distribution of carbon in blister steel can be improved by both mechan-
ical and chemical means. On the one hand, the bar was cut into pieces and then
those pieces redistributed. The rearranged bar would then be re-consolidated
by welding at the forge and anvil. This cutting, rearranging and welding
might be repeated two or three times to the improvement of the material.
Chemically, however, there is another process occurring called 'carbon migra-
tion'. The carbon in a rudimentary piece of steel will naturally seek an even
distribution, moving from areas of high carbon content to areas of low carbon
content. So, just heating and forging a piece of blister steel will improve it.
Moxon, writing about 1680, writes of steel, its use, shaping and heat treating in
terms that any modern blacksmith will easily understand. This is ancient, tradi-
tional knowledge that by Moxon's time was centuries old.
Steel is desirable and available but expensive. It is unusual to find an histor-
ical tool of any size like a brick axe that is composed entirely of steel. Instead,
the common strategy was to make the bulk of the tool from bar iron and weld
a piece of steel only where it was needed, typically along a cutting edge. The
advantage was reduced cost with little or no loss of utility. The alternatives do
not seem nearly as likely on any tool that needed a long lasting edge.
The first alternative would simply be a tool like a brick axe of bar iron - an infer-
ior tool in constant need of sharpening. Even hammer-hardened iron, a process
also recognized by Moxon, is pretty worthless as a cutting tool. If a joiner could
have a steeled or 'lined' (as it came to be called) chisel, if a charcoal burner
working on the edges of society could have a felling axe with a steel bit, why
would not a journeyman mason or brick hewer enjoy a similar advantage?
The second alternative would be a case hardened edge. Case-hardening is
described by Moxon and even in the twelfth century by Theophilus. Briefly,
case-hardening is a superficial application of the cementation process that
made thoroughly carburized steel. Iron is baked in a carbon rich environment
(often surrounded by ground charcoal or pieces of leather, bone or horn) from
which oxygen is excluded. The surface of the iron absorbs carbon, turns to
high carbon steel and will harden upon quenching. Theophilus describes case-
hardening for making smaller sized files (Chapter 19), but in general it is fairly
worthless for an edge tool that must be sharpened. On the first or second sig-
nificant edge touch up, the hard steel will be ground away. This is particularly
true for a tool like the brick axe that is sharpened to a symmetrical, knife-edge.
With the steeled edge, the tradesman gets the best of two worlds. The bulk
of the tool is made of a tough, relatively inexpensive bar iron, but where the
work is done a hardened and tempered piece of steel provides a wear resistant
edge. Yet, even the best steel most carefully heat-treated needs eventual sharp-
ening. Your [Gerard Lynch] account of 1482 that records brick axes being
sharpened every two to three weeks on the work done for Kirby Muxloe Castle
does seem odd. I suspect that a brick axe does not need the keen edge of a
