Paper cutting (in slicing motion) is
NOT a good way to check the edge condition of the knife.Even a knife with pretty dull edge can still do paper slicing.
(Or, more importantly, a knife that really can’t do paper slicing
can still cut things.
So, doing the edge retention test using paper slicing to judge
if the knife’’s still retaining the edge is a moot point.)
Here are some examples of practical edge test that will tell you
how sharp your edge really is.
#1 Sharpie testPlace the blade at some angle (between 45° and 30°), and
see if the edge slips.
If the edge doesn’t catch sharpie, that knife needs to be
sharpened ASAP.
A knife in this condition is (somewhat) more dangerous.
Because, as you can see in the video, knife edge
degradation doesn’t happen evenly on all across the blade.
Usually one part (that gets used the most) becomes dull,
so when you are using the knife, it slips on this portion,
and the tip (which still is sharp enough to cut your flesh)
will hit your hand.
This test can also be used to figure out the angle of the bevel.
#2 Hair popping test
Can you hear the “popping sound”?
This is a good test for both kitchen and EDC knives.
If the edge is sharp enough, it’ll catch the hair and cut.
If it’s not sharp enough, it’ll slip over the hair.
“Hair popping” and “hair shaving” sharpness are two different things.“Hair shaving” is less sharp than “hair popping”.The main problem with this test is,
that not everyone has the hairy arms (or legs),
and pretty soon, you’ll run out of hair to test the edge.
#3 Push cut testPick up some thin and flimsy paper,
and try to push cut it without slicing motion.
This is also a very good test for both
kitchen and EDC blades.
#4 Action paper cut testThis is more fun.
Try it!
Cutting diagonally is even more fun, but harder.
Not only the edge needs to be sharp enough
to catch the grain of the paper,
but also it has to have the right dimension
to slice through the rolled paper
without knocking it over.
(But, you don’t really need this level of sharpness
in the real world use.
Still, it is worth trying, and it’s a lot more fun than
same old paper slicing.)
#5 Rolled up rag cut testProbably the most practical test.
You can clearly see the difference in the edge performance
by how deep the knife cuts in.
You will also quickly notice that applying extra force doesn’t make
the cut deeper.
#6 Cut / Whittle free hanging hairThis level of sharpness is not needed in the realistic situation.
Better spend the time and energy for something else.
(Seriously. Unless you are really obsessed.