Best way to tell if a knife is sharp?

Taste test

Properly clean the blade of all debris and residue from use and/or sharpening. Hot soapy water is usually sufficient, but environmentally friendly solvents may be used in conjunction for particularly stubborn foreign matter.
Dry thoroughly with a soft cloth, terry is preferred.
Place the edge on your tongue. The taste buds near the tip, which generally associate with sweet flavors, seem to work best.
Lick along the entire length of the cutting edge, to check for consistency in sharpness along its length.
If the knife tastes like blood, then it is sharp enough.
If the knife successfully passes the test, have someone contact medical assistance for you. You will likely not be able to properly enunciate at the completion of the test.

warning - the presence of a metallic tongue piercing may damage the delicate edge of your knife, use caution.
 
By touch, using my thumb, or if it will pop hair. Another way I rarely use is, when I cut myself and don't notice until I see the blood.
 
Because paper makes a mess, and I only have so much hair on my body, I touch the blade with the tip of my finger.
 
Knives do not have to be razor sharp to work, they just need to be sharp enough to cut what you need to cut.

n2s
 
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Moose
 
i just run the blade lightly over my fingernail from bottom to top. if it slips anywhere i know where to focus more of my time sharpening.
 
hardheart said:
Taste test

Properly clean the blade of all debris and residue from use and/or sharpening. Hot soapy water is usually sufficient, but environmentally friendly solvents may be used in conjunction for particularly stubborn foreign matter.
Dry thoroughly with a soft cloth, terry is preferred.
Place the edge on your tongue. The taste buds near the tip, which generally associate with sweet flavors, seem to work best.
Lick along the entire length of the cutting edge, to check for consistency in sharpness along its length.
If the knife tastes like blood, then it is sharp enough.
If the knife successfully passes the test, have someone contact medical assistance for you. You will likely not be able to properly enunciate at the completion of the test.

warning - the presence of a metallic tongue piercing may damage the delicate edge of your knife, use caution.
Click to expand...

This one is definitely my favorite way.
 
For kitchen knives, an excellent test is to try slicing a ripe tomato. If you can make thin slices on thin-skinned tomatoes, the knife is quite sharp for kitchen use.
Faiaoga :cool:
 
I test by splitting a hair. If im going to the extremes. The hair severs with a tiny pop when I te.ouch it on the edge phonebook paper cutting is a decent test
 
I like to use the "samurair hair test", gently scrape your hairs to feel the catch without severing any hairs, quite handy if you dont want to shave your arms but it is less accurate than thumb testing, i generally use it on random knives that i know arent very sharp.

I use my left arm hairs as a sharpness test field very often so my forearm is quite bald all the time, i keep my right arm relatively virgin and use it for treetopping tests,
I kept a bunch of beard hairs as well but they are overly thick so this isnt as accurate as my right arm for HHT and treetop tests.
I occasionnaly use cigarette rolling paper (Rizla silver, very thin) to do slow slicing strokes, this is really uncompromising as the slightest drag will tear the paper.
One way i started to use recently is slicing calluses off my palm.
 
My true test is to take a pair of those disposable foam ear plugs and slice off little wafers.

If the knife is not ground/sharpened correctly it'll crush the foamif it's sharp it'll slice through like styrofoam, try it you'll see what I mean. It takes a sharp properly beveled knife to do this.
 
I use a variety of tests.

Least sharpest: It should be able to SLICE printer paper
Next up in sharpness: It should be able to cut hairs with a tiny bit of sawing motion
Next: Slice phone book paper (Should be able to pop hairs at this point, and if it doesn't a few more strops on each side will make it do so)
Next: Push cut printer paper
Next: push cut phone book paper
Most sharp: Push cut phone book paper with not alot of noise, this means it's ready for shaving( unfortunately all I have for that is a Ja henckels paring knife I have at about a 50 inclusive, but other than that a Mora topq craftline whatever, it's in 12c27 a shaving steel)

NOTE: I don't like the finger nail drag trick, because for a edge to be able to push cut something, it needs a polished or more refined edge. And a polished edge won't grab anything. That trick only works if I leave on the burr after using aluminum oxide stones. I primarily use Arkansas stones to sharpen, and they polish even though they are a lower than typical polishing grit.

Also, I can make curly cues from nails with an edge that can't cut paper. I think that's mainly to do with geometry.
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Nice thing about sharp edges is they barely bleed, like a few drop of blood, just because you've doing more splitting apart the cells than ripping apart.

Sucks to get a cut on a knuckle though. Got out on my left pointer finger and with a centimeter square flap all the way through the skin. And that thing took at least a month before I didn't have to put a band aid on it all the time. Though I never immobilized it, I just put the skin glue on it, which unfortunately got caught on something when it was almost healed at like 2 weeks(I had edge of glue on my knuckle because it's just always moving, I"m sure it would work a lot better on a non stretching piece of skin.) So the glue got ripped off, along with the skin underneath.
 
I'm a little OCD when it comes to edges anymore, so my main tests involve hair whittling and tree topping. A decent edge needs to effortlessly whittle down the entire length of the blade. If you get to a spot where it just plays fiddle, you need to go back to one of your finer stones or pasted strop. The thumbnail test is good for judging bevel evenness. For most folks, this goes beyond a "working edge", but it's just what I do, personally.
 
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