View Full Version : Sharpening - how do you "check your work"?

04-07-2013, 11:57 PM
So as I try to get better at sharpening, one of the problems I find myself encountering is the lack of a quick feedback loop. What I'd like to be able to do is sharpen up a knife, then test it somehow, and then either resharpen it or call it a day depending on whether it passes.

The internet is full of all sorts of folk tests: Shaving your arm hair, taking a curl off your thumbnail, slicing paper, cutting a tomato with no pressure, whatever. The internet is also full of people saying that some or all of those are silly tests that don't make sense for a kitchen knife.

So, my question in two parts:

1. How do you test that a knife is actually sharp when you're done sharpening it?

2. How do you do interim tests along the way, if you use multiple stones? That is, what convinces you that you've done a good job at the 1000 grit stone and are ready to move the knife up to a finer stone?

04-08-2013, 12:04 AM
Feel the edge w/ your fingers. Not much help to someone who isn't very experienced, but with time, is one of those things you "get".

Cutting paper. Pull and push cut.

3 Finger test:


And a few from Jon @ JKI:


04-08-2013, 12:04 AM
I look at the edge for changes in the way light reflects on the edge, feel the edge with my fingers for "stickiness" and then sometimes shave some hair off my hand just to see if it catches free-standing hairs. Sometimes I will cut paper or a tomato but these days, that's just for kicks. For razors, I will use the fingernail test before I do any polishing just to make sure the edge is free of major imperfections.

04-08-2013, 10:38 AM
i look for burrs with my eyes and finger tips. if there are any then i strop on a fine stone or run through hard felt or cork, whichever's lying closest to me. then check again, if none are found then i strop 2x on each side on my finest stone then:

arm hair, then paper then tomatoes.

really depends on what kind of edge i want though.

04-08-2013, 10:51 AM
An edge has many properties, not just 'sharpness', so I like to do as many tests as I can to gather data about the edge.
#1 Three finger test
#2 Cigarette paper cut
#3 Tissue cut, in both directions
#4 Printer paper cut (newspaper for euro knives), along all areas of the edge
#5 Loupe, if I can feel chips with the paper cut
#6 Microscope
#7 Hair whittling testing
#8 Rolled tissue paper cut, depending on the type of edge I'm after

It's rare that I will use all of them on one knife that's being sharpened, but at least 2 or 3 get used. Always the three finger test though, unless they're numb or overly moist.

04-11-2013, 11:14 PM
considering I sharpen 2-3x/week for work, I don't even bother. at this point I know it will be at least "good enough".

04-11-2013, 11:35 PM
um, cut random stuff up!

04-11-2013, 11:46 PM
What Panda said. I almost always have potatoes around, and I sharpen at night, so I dice some for hash in the morning, or grab a tomato or something.

04-12-2013, 08:45 AM
I have a few knives in rotation, I'll sharpen one, and take one that I know to be already sharp to work. I use the newly sharpened one throughout the day, if its good I keep using it, I can tell if its bad after about 30 mins, so I trade to my other knife and re-do it that night.

04-12-2013, 02:46 PM
One thing I do that is foolish and perhaps a bit dangerous, is test the edge on the hair on the back of my head. If the blade grabs immediatly, the edge is good enough for use in my home kitchen, if it slides at all, I strop, ceramic rod or sharpen then try again.

04-12-2013, 02:55 PM
I generally have 2 tests at the end. I cut a tomato to make sure the edge is where it should be. If I have done any thinning I also cut a large root vegetable to make sure I did not screw up the geometry. In between stones I cut into felt, and can tell its progression by how deep the cut goes.

04-12-2013, 05:59 PM
I test only after heavy geometry change, or an unknown knife. My first edge after geometry change is often weak. With blades I'm familiar with, I'm quite confident. Perhaps very fine cigarette paper, for fun, or a three finger test before applying a single microbevel la Jon Broida. My best test is Cr2O3 acrylic paint leather to be sure about burr debris.
There are a lot of parameters, but essentially you know long before you've reached your finest stone whether it will work or not - afterwards.

04-12-2013, 06:06 PM
Thumbnail and three finger tests, those two will tell me what I need to know.

04-12-2013, 06:19 PM
I like the Kramer test on enameled magazine stock - the slick stuff. Bend a page the try to cut the round part at a steep angle - now that's sharp. It's different for different tasks - a boning or slicing knife want a different finish. For boning not so highly polished - it's going to do some tough work and will get a touch up with the steel during the process especially if you are breaking down primals. For a general knife 6k followed by cardboard and newspaper strop works for me. For boning I go 1k. Deba or fillet knife maybe 3k they are doing tough work - and I still strop after the stone.

Chef Doom
04-15-2013, 03:32 AM
I go fight bears. Preferably grizzly bears. You will make sure your work is done properly when your life depends on the edge of the knife.

Unfortunately I have been officially banned from any and all federal parks, state parks, zoos, national wildlife preserves, carnivals....

04-15-2013, 10:27 PM
I use the finger test and then try to slice through some thin paper

05-06-2013, 11:46 PM
Hehe, I've been slicing an orange or grapefruit (I wanted to make some marmalade recently). If I can slice a less than 0.5mm thick slice off the orange through the central pith without crushing any of the juice cells, I call my knife sharp enough to use.

Paper is abrasive, I have no desire to waste the very shapest edge by cutting paper before I use the knife to cook with.


05-07-2013, 03:04 PM
I just started the 3 finger thing a couple weeks ago and it's now a std for me. So -

1 - check for burrs runing my finger along the side of the edge and also to the edge. (direction is spine to edge) feeleing for any difference between the 2 sides and front to back. Same finger or thumb if possible.

2 - then the three fingers. that tells me no only how sharp the edge is but also how toothy or grabby it is. I never realized there was that much difference!

3 - slice a floppy paper towel to see how much pressure and clean the cut is.

4- then give it to my wife to shave a little skin off a grapefruit. A really really good edge doesn't cause the edges of the cut to "bleed" or weep. Then I start over until I get it right.

05-07-2013, 03:06 PM
Hehe, I've been slicing an orange or grapefruit (I wanted to make some marmalade recently). If I can slice a less than 0.5mm thick slice off the orange through the central pith without crushing any of the juice cells, I call my knife sharp enough to use. Peter

Peter - have you notices any dulling of some blades when slicing the peelings from grapefruit? My soft blades with way to thin bevels seem to actually lose the edge.

05-07-2013, 03:34 PM
when i sharpen kitchen knife I usually cut food with it and when its a chisel Im sharpening its usually wood.

05-07-2013, 09:32 PM
Never noticed any dulling so far, but grapefruit is quite acid and the peel leaves sticky oil on the blade that dries rapidly. You might have a sticky rather than dull knife.


05-10-2013, 12:15 PM
I'll push/pull cut on newspaper to see if there are any inconsistencies in the edge, then I'll roll the newspaper and cut on angle (in the air) and then thumb nail test. Also Carters three finger test is how I check during sharpening, it gives pretty immediate feedback.

05-10-2013, 12:28 PM
Maybe I'm old school (and it looks kind of weird, but I do wear long sleeve shirts a lot), but I always try to shave some arm hair. I first try the tip, then the belly and finally the heel. That way I can test to see which areas need work. If all three sections will shave it clean, then I know that the knife is finished. In my defense, I'm used to working in wood-fired ovens and over flames, so half of my arm hair has always been burnt off anyway.