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What is sharp?
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  1. #1

    What is sharp?

    Hi all, a newbie asking a daft question but I hope not too daft. How can we measure sharp on a scale of 1 to 10? Is paper slicing 1 lowest or best. Is bald arm highest or lowest.

    I don't have a scanning microscope so would appreciate some pointers. Yes I am happy with my blades but could they be better?

    Any thoughts?

  2. #2
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    If you pluck out one of your hairs, hold it between thumb and forefinger and then manage to cut or even split it in front the fingers, in the air, your edge is about as sharp as it can get. That's pretty much the ultimate test.

    paper-cutting sharpness is easily enough for pretty much anything you can do in a kitchen, though.

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    The videos this guy makes are probably some of the best on youtube as far as sharpening is concerned, they are only in German, though.
    In this one he presents several sharpness tests:





    - checking for glinting edge (glinting = blunt)
    - feeling with your thumb (requires experience though)
    - checking with a plastic pen or fingernail if the blade "grabs". Great for checking the angle of your bevel, too.
    - checking with the hair on the back of your head
    - paper test, if the blade catches at one point there is still a blunt part of the edge
    - kitchentissue test
    - shaving test - must work from both sides, if it only works on one side it is due to a burr!
    - hairsplitting test. He says if you can do that without use of a strop it is due to a burr, not because of a good edge.
    - the hanging hair test for razors
    - tomato test with old mushy tomato, tomato drop test. According to him those are not truly conclusive.


    He himself prefers the thumb test and the armhair shaving test. If your blade was damaged/chipped, the paper cutting test is useful.

  4. #4
    Senior Member Birnando's Avatar
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    Sharp is a highly relative term.
    One mans sharp is another mans blunt.
    Toothy edges are the preferred edge for some, others prefer highly polished and fine toothed edges.
    Others have both, depending on the job at hand.

    There are a variety of tests out there, that all works to some extent.
    It's just a matter of finding what works as a yardstick for you.
    The Hanging hair test, the arm-hair test both tre-topping and base, the thumbpad test, the three finger test, the finger nail test, the paper cutting test and so on and so on.

    That said, a test is worth only so much.
    Using the knife at its intended use is really the only one that matters.
    imo

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    I think armhair shaving and paper slicing are pretty easy. However, a buffed/rounded edge will do pretty OK at both tasks and not cut capsicum or tomato skin without a good deal of effort. Such tests can be done below 1000-grit and pass pretty well.

    Hanging hair test is OK and works for razors, but is largely unnecessary for a kitchen knife and might not be indicative of anything that you need a kitchen knife to accomplish.

    I see lots of rubbish tests on YouTube, from slicing tissue paper to severing pineapples to dropping tomatoes or the ubiquitous sitting tomato thin-slice test...all of which can be done with mediocre edges.

    I do slow paper slicing to feel my bevel consistency (after visual inspection), but the real test is food. Carrot, garlic, mushroom, and bell pepper cover most of the bases, but one might want to add a meat/fat/silverskin test depending on the knife style.

    Just my opinion though, could be way off.

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    For me, it must at least be able to slice paper smoothly, the lowest requirement.

    paper-cutting sharpness is easily enough for pretty much anything you can do in a kitchen, though.
    This.

    I learned not to make fruit knives too sharp because my uncle always risks cutting his fingers when peeling and cutting fruits. Even paper-slicing sharp is overkill for cutting fruits. For utility knives, razor sharp is a must.

    Paper test is great during the honing process, you will straight away see which part is still blunt and you focus-grind that part until no light is reflected anymore.

  7. #7
    Senior Member Geo87's Avatar
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    What is sharp?

    Defining sharp is tricky. A saw cuts wood well but an onion terribly. A chef knife cuts a onion well but wood terribly... Both would be considered sharp . Therefor I think a sharp knife is something that excels at its intended purpose.

    Test straight razors on hair but kitchen knives on food.
    I personally like overripe tomatoes carrots onions & mushrooms.

    Overripe tomatoes:tests toothyness & that the edge is not rounded, knife should bite in straight away.
    Carrot tests: for any wedging issues, should cut clean and not split it apart
    mushrooms: should cut cleanly without damaging or squashing
    Onions : should ' fall through' with ease

    I would ovoid shaving your arms ... Not a good look

  8. #8
    Quote Originally Posted by Geo87 View Post
    Defining sharp is tricky. A saw cuts wood well but an onion terribly. A chef knife cuts a onion well but wood terribly... Both would be considered sharp . Therefor I think a sharp knife is something that excels at its intended purpose.

    Test straight razors on hair but kitchen knives on food.
    I personally like overripe tomatoes carrots onions & mushrooms.

    Overripe tomatoes:tests toothyness & that the edge is not rounded, knife should bite in straight away.
    Carrot tests: for any wedging issues, should cut clean and not split it apart
    mushrooms: should cut cleanly without damaging or squashing
    Onions : should ' fall through' with ease

    I would ovoid shaving your arms ... Not a good look
    My wife thinks the shaved arm is alopecia match in g my bald head. But slightly seriously, thanks you and all the respondants, I am starting to believe my knives are adequate.

  9. #9
    I find that it does not matter what method you've chose stay consistent with it. With time you will develop an understanding sharp, sharper, wow if you keep doing the same test(s). I usually stick to phone book like paper test.

  10. #10
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    Quote Originally Posted by Geo87 View Post
    Defining sharp is tricky. A saw cuts wood well but an onion terribly. A chef knife cuts a onion well but wood terribly... Both would be considered sharp . Therefor I think a sharp knife is something that excels at its intended purpose.

    Test straight razors on hair but kitchen knives on food.
    I personally like overripe tomatoes carrots onions & mushrooms.

    Overripe tomatoes:tests toothyness & that the edge is not rounded, knife should bite in straight away.
    Carrot tests: for any wedging issues, should cut clean and not split it apart
    mushrooms: should cut cleanly without damaging or squashing
    Onions : should ' fall through' with ease

    I would ovoid shaving your arms ... Not a good look
    I certainly agree with the comments regarding onions and mushrooms; these tests are very telling.

    I also use capsicum (bell pepper) as a good indicator of sharpness as I use it frequently. For me, a sharp knife will drop through the skin with almost no pushing or pulling action and very little force. A dull knife will require a lot of force and hit the board pretty hard despite only moving the thickness of the capsicum, or 3-4mm.

    Cheers,

    J

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