The myth of the razor sharp sword
There are certain things that need to be extreamly sharp to do
their jobs, such as a surgeon's scalpal or a razor blade and these
items are designed with edge sharpness as their primary and practically
only feature. In order to acheive and maintain this fine of an
edge, the steel needs to be extreamly hard. Hardening the steel
to this point will also make it very brittle, so only small blades
can have edges like this. You can not simply scale up a razor
blade to sword length, doing so would result in a sword so brittle
it would shatter on impact like glass. To make a blade the length
of a sword requires a series of compromises and carful balancing
of properties. The blade needs to be hard enough to hold an edge,
but not so hard that it can shatter. It needs to have some rigidity,
but flex enough to absorb impact. Becasue a sword length blade
can not be as hard as a razor blade, it will not hold the same
edge as a razor blade. If you were to sharpen one up to that degree,
you would find that it would dull itself very quickly. The combination
of an extreamly thin edge without the extream brittle hardness
will result in the edge rolling and folding over on itself very
quickly. The end result is a blade that never stays very sharp
because it was “over sharpened” in the first place. Think about
how quickly a razor blade gets dull just from cutting whiskers.
Now take a nesisarily softer piece of steel and subject it to
significantly harder cutting materials and you get the idea.
Cutting paper, sure it looks cool, but...
This is something you have probably seen a lot. People like to
show how sharp a blade is by cutting paper with it. With a knife,
this can make some sense, some knives can be extreamly sharp,
but with a sword, not so much. I have heard people criticize a
sword saying that “it can not even cut paper” as if paper cutting
is a prerequresite first step before being able to cut flesh.
However, the truth is the opposite. When a sword blade is to the
point of cutting paper it is getting past where it needs to be
to function as a weapon and is closing in on becoming “over-sharpened”
leading to an edge that will fold and not stay sharp. Being able
to cut paper with a sword blade is about the pinacle of blade
sharpness, not a starting point. Realistically, you should not
be expecting most swords to ship quite this sharp for many of
the reasons listed above.
So how sharp should a sword be?
A sword is simply a tool, a tool designed for the single purpose
of killing other people, but a tool none the less. Like any tool
it should be sharp enough to do it’s job and no more. Historically,
a lot of swords were typically not as sharp as many people seem
to assume. Many European Medieval swords were not super sharp.
Some people say "butter knife" sharp, but think more
like a kitchen knife that needs a touch up. The reasoning for
this is simple, they did not need to be any sharper. Swords intended
for battle would be given edges designed to survive as much battle
as possible while still being able to perfrom their intended purpose.
A sword does not require a super sharp edged to do it’s job, the
combination of a moderate edge and force behind it is enough to
split skulls and remove limbs. An edge that is super sharp does
not actually perfrom these tasks any better in a real world situation,
but will dull and chip faster. So swords were sharpened up to
the degree that they would function without becoming too fragile.
They were not sharpened up to impress other warriors by shaving
hair off their arms or slicing pages out of illuminated manuscripts.
The goal was to have enough “meat” on the blade edge that it would
not be too damaged from an errant shot into a shield rim or plate
If it's not sharp it's dull
People argue about this all the time, but I think a lot of the
argueemnt stems from people using the terms differently. A lot
of people seem to think of sharpness in black and white. "Razor
sharp" or "dull". There is some logic to this,
if your razor is not razor sharp, it would be considered dull.
Knives are usually thought of the same way, once they are not
super sharp, they are now "dull" and need to be resharpened.
But swords are different. A sword with an edge like a dull razor
blade would be considered "extreamly sharp". This is
where I think people get mixed up. "sword sharp" is
not really the same as "knife sharp", so "dull"
on a knife can still be "sharp" on a sword. In essence
a blade moves from sharp to dull when it stops being able to perform
it's intended function. For a razor, that function is shaving,
for a knife it could be filleting meat, but for a sword it can
continue functioning at a far duller level by comparison with
other types of bladed tools. Sharp is really not a word that can
be used on it's own, the exact meaning of the term changes depending
on what the sharp object is. Think of a "sharp" stick.
The threshold of what makes a stick sharp can not even be compaired
to what is required to make a razor blade "sharp".
So did they have sharp swords or not?
The short answer is yes, but we need to adjust our perception
of "sharp" and remember to understand swords for what
they are and not think of them as scaled up knives. The threshold
of where a sword moves from dull to sharp is lower than a knife,
do to the way it is used. To be clear, you can sharpen most sword
blades up to "razor sharp". The question is if they
should be that sharp and if historic ones ever were. Despite the
history, some people like their swords that sharp and there is
nothing really wrong with that. Just know that some sword blades
will not hold that type of edge and others will become fragile.
A sword that is "too sharp" will dull quickly and chip
What about Katana?
The katana is considered by many the sharpest sword type in history.
While most other sword types had to balance the opposing properties
of hardness for edge retention with softness for flexability and
shock absorbsion, the ingenious Japanese smiths developed a work
around, actually a couple of work arounds. Blade lamination and
diferential hardening. The Japanese were not the first to make
laminated blades, but their process is important for our discussion
of sharpness. Without going into great detail about lamination,
you can think of the blade as a steel sandwich. The core or meat
of the blade is made with a high carbon steel providing a very
hard edge at the expense of being brittle. That hard core is then
sandwiched with a softer lower carbon steel on the sides of the
blade. The result is a blade with a very hard edge but a softer,
more flexible spine. Expanding on this concept is differential
hardening. In a normal blade hardening process the blade is heated
to red hot and quickly quenched in water or oil. This will produce
a very hard but somewhat brittle blade. With diferential hardening
the back of the blade is insulated with clay. This way when the
sword is quenced the edge cools quickly while the back cools slower.
The result being a very hard edge with a softer spine.
The combination of these techniques along with the geometry of
a katana edge can allow it to take and hold a sharper edge than
can normally be acheived on a different sword type. However, the
resulting edge can still be somewhat brittle, so the cautious
Samurai would be selective on when he would use this prized katana
and would likely choose to dispatch more enemeis, especially armored
ones with the Yumi (bow) or Yari (spear). This leads us to talk
about how little action swords actually saw through most of history
compaired to other weapon types, but that's for another day.
So remember, when talking about sword edges, try to adjust your
perception of "sharp" into sword mode and try not to
think of it as just a big knife.