True Swords Are Made By Skilled Smiths
 A superior
way to balance hardness and toughness is through steel with non-uniform
properties. This can be achieved through differential hardening, differential
tempering, differential density, differential carburization, or through
mechanical or crystalline Damascus techniques. Metallurgy is science,
but it is also art, a dance where many techniques may be used to obtain
the desired result.
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Differential Hardening – This technique is
seen on traditional Japanese swords, but also can be applied to other
designs. It is based on cooling the edge more rapidly than the spine,
thus giving the edge a higher hardness. Differential hardening can
be accomplished by quenching just the edge; or by using clay to insulate
and retain heat in the spine while quenching the whole piece.
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Differential Tempering – Applying a lower
level of heat to steel removes some of its hardness, giving it added
flexibility and toughness. The amount of flexibility or toughness
in different parts of the blade can be controlled through differential
tempering.
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Differential Density – Some smiths believe
in this technique, while others just as strongly claim that is has
no basis or value. In any case, the concept is that the edge of a
blade can be packed more densely than the body through hammer blows,
thus giving it additional strength and hardness.
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Differential Carburization – This takes advantage
of the fact that every flame has three zones – oxygen rich,
neutral and carbon rich – and that, depending on where it is
in a flame, steel may either lose or gain carbon at the same rate,
to a depth of about 1/8 inch per hour. Used properly, a smith can
add carbon to a blade’s edge to increase hardness while retaining
the spine’s flexibility. Unfortunately decarburization, the
result of inadequate knowledge or training, is a frequent problem
that adversely affects the quality of many blades.
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Mechanical Damascus – This technique combines
two or more dissimilar irons or steels through forge welding and then
folding or twisting the resulting steel to produce the characteristic
Damascus pattern. This is one of the oldest ways of converting iron
to steel.
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San Mai – A “steel sandwich” where
a central layer of hard steel has one or two outer layers of tougher
steel. Roman short swords were frequently made this way, as are many
Swedish knives.
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Crystalline Damascus –True Damascus steel,
sometimes known as wootz or bulat steel, is not folded steel. Instead,
Crystalline Damascus achieves its characteristics through the segregation
of a single steel into multiple steels with different carbon contents,
crystalline structures and alloy levels. The making of this steel
was long considered a lost art, but today a handful of smiths have
rediscovered techniques for producing true crystalline Damascus steel.
Most smiths are happy to master even one of these techniques, which
they then apply to all their work while criticizing other methods.
But these techniques are not mutually exclusive. To the contrary,
they can and should be used together to meet the desires of the smith.
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