are certain things that need to be extremely sharp to do their
jobs, such as a surgeon's scalpel or a razor blade and these items
are designed with edge sharpness as their primary and practically
only feature. In order to achieve and maintain this fine of an
edge, the steel needs to be extremely 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. Because 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 extremely thin edge without the extreme 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 necessarily 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 extremely 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 prerequisite 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 pinnacle 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
perform 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 perform 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 armor.
If it's not sharp it's dull
People argue about this all the time, but
I think a lot of the argument 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 "extremely
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 compared to what is required to make a razor
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 easier.
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 flexibility and shock absorption, the ingenious Japanese smiths
developed a work around, actually a couple of work-a-rounds. Blade
lamination and differential 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 differential hardening the back of the blade is insulated
with clay. This way when the sword is quenched 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 achieved 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 enemies,
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 compared to other weapon types, but that's for
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.