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14 ways to test how sharp your knife is
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14 ways to test how sharp your knife is

14 ways to test how sharp your knife is

Quite a while back now we wrote a short article about how to check if your chef’s knife needs sharpening. In that article we quoted a three part test suggested by Alan McKee in his guidebook ‘Sharpening’.
Of course if you scour the interwebs you’ll find quite a few ways of testing knife sharpness, so we decided to do a poll of the most commonly suggested tests out there. This poll would probably not pass any ‘statistical significance’ tests itself, but it did highlight which were the most recommended methods along with a host of others!

So here are the tests, in order from most to least recommended.

1) Cutting paper

Votes: 10
This is probably the best known test – simply hold up a piece of A4 paper (edge up) and slice down into it. If it slices smoothly through the paper, you have a sharp knife and if it catches on the paper or tears it, your knife needs sharpening. You shouldn’t have to use any force – the weight of the knife itself should be enough. You can also use this test to see if your blade has any dull spots if you slice through the paper moving the blade through as you cut – a dull spot will slow the movement or just stop cutting cleanly.

Some experts also suggest cutting through glossy magazines, phonebooks (if you still have any), cardboard and finally toilet paper, which is apparently the toughest test. If you want a slightly tougher test using a piece of A4 paper, put the top and bottom edges together to make a rounded target and see if the knife will cut through that.

2) Cutting the hair on your arm

Votes: 6
This is also a very commonly suggested method, but you do need to be pretty careful! The blade does not need to touch the skin, it should just slice through the hairs if it’s sharp. If you have to test a lot of knives yo might run out of hair to test it on, but at least it saves a trip to the beauty salon.

3) Cutting a tomato

Votes: 5
Again this is a commonly known test and with good reason. Any sharp knife should be able to cut through tomato skin with no downward pressure applied. If you have to push down at all to break the tomato skin, your knife needs sharpening. Also cutting a tomato with a blunt knife will result in it getting a little squashed in the process.

4) The nail test

Votes: 5
This test involves using your fingernail or thumbnail – you very gently tap the blade edge on your nail – a sharp blade will catch a little, a blunt blade will slide away. You can use this test up and down a blade to detect any dull spots. See also pen barrel test below.

5) Cutting an onion

Votes: 4
Very similar to the tomato test. You shouldn’t need to ‘saw’ through the onion with a sharp blade.

6) Visual inspection

Votes: 3
Even with the naked eye it’s possible to see imperfections and chips in a blade with a light source behind you. It’s even easier with a magnifying glass or even one of those inexpensive mini microscopes you can get at a two dollar shop. Ideally the blade should appear as a smooth black line.

7) Finger/thumb test

Votes: 3
You also have to be very careful with this test. You draw your the tip of your finger or thumb very gently across the blade, applying no pressure (never along it). If the blade is sharp, you should be able to feel the indentations in your fingerprint catching on the blade edge.

There is a variation of this called the ‘Three Finger Test’ which does involve moving your finger tips along the blade. This technique is outlined in this video on YouTube – we recommend extreme caution!

8) Cutting fruit/vegetables

Votes: 3
Again much like the tomato test. Suggested fruit include green apples and limes.

9) Ballpoint pen barrel test

Votes: 1
This is exactly the same test as the fingernail/thumbnail test above. A sharp blade should dig slightly into the plastic of a biro barrel. Maybe not use your Montblanc.

10) Styrofoam/cork/balsa test

Votes: 1
A more hardcore version of the paper test. Pool noodles are also quite good apparently. And fairly cheap.

11) Hair whittling test

Votes: 1
Not quite the same as the arm hair test. Hair whittling is where you can slice pieces off a single strand of hair. Unsurprisingly, you need an extremely sharp blade to do this. Here’s a video.

12) CATRA test

Votes: 1
We covered the CATRA test here. If you’ve got a $1,000 bet on who has the sharper knife you can send both to Sheffield in the UK, pay their fee and you’ll get the verdict.

And two we wouldn’t recommend…

13) Tsujigiri

0 votes (just a mention)
This refers to the supposed practice of samurai in Japan testing a new sword – or ‘katana’ – on a poor unsuspecting random victim in the street. There is some doubt that this actually happened, with a mistranslation of the Japanese word for ‘test cutting’, given its similarity to another word which means ‘crossroads killing’. Or maybe a budding samurai simply misheard his sensei. Read more about Tsujigiri here.

14) Tongue test

0 votes (just a mention)
This guy says he can tell if a blade is sharp by licking it. Here he is (he licks the knife at the 8:50 mark).

Do you use any other techniques we have not referenced here?

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