The Cutting Edge or How Sharp is your Knife?

Take your best knife out and look at it close­ly. How sharp is it?

Prob­a­bly not as sharp as you think it is.

Here’s one of my favorite knives, a 7 12 inch Chi­nese cleaver:

Chinese Cleaver

Looks pret­ty sharp, eh?

Let’s look at it a bit clos­er, at about 3X power:

Still look pret­ty sharp? Let’s try it at 150X power:

Now you can see lots of bumps and grooves, and the edge is uneven, too. And this knife has been run through an Accusharp V sharp­en­er recently.

But a V sharp­en­er or a sharp­en­ing steel don’t put a new edge on a knife, all they do is smooth out some of the rougher parts of the edge you have.

So, it’s time to give this knife a good sharpening.

There are sev­er­al dif­fer­ent types and grades of sharp­en­ing stones you can use, but in gen­er­al they all come down to two fac­tors: The grit num­ber and the wet­ting agent.

I’m cur­rent­ly using a Lan­sky knife sharp­en­ing kit that has 5 stones, rang­ing from real­ly coarse (70 grit) to fair­ly fine (1000 grit.) Sharp­en­ing stones go all the way up to 6000 grit.

The wet­ting agent keeps the sur­face of your stone from get­ting clogged up, basi­cal­ly the oil or the water float away the met­al par­ti­cles you grind off the knife as you sharp­en it.

The stones in my Lan­sky kit use oil as the wet­ting agent, I think oil stones are a bit eas­i­er to main­tain. There are also water stones, which gen­er­al­ly need to be soaked in water for a few min­utes and washed off after­wards. There are stones that say they can be used dry, but you’ll need to refresh the stone peri­od­i­cal­ly, pos­si­bly even grind it down, or at the very least clean it with a toothbrush.

When using sharp­en­ing stones, you want to start with a coars­er (low­er) grit stone and work up. Because this knife is already fair­ly sharp and does­n’t need a whole new edge, I’m going to start with the ‘medi­um’ stone in my kit, which is a 280 grit stone.

To use a stone, start at the heel of the knife and work towards the point. If you use a man­u­al stone, push the knife across the stone, blade first, while slid­ing the knife side­ways towards the tip. (There are many very good videos of the prop­er sharp­en­ing tech­nique on the Inter­net; the main pur­pose of this post is to show you what your knives prob­a­bly look like and hap­pens when you sharp­en your knives–at a micro­scop­ic level.)

With my Lan­sky kit, the knife remains fixed and the stones moves across the knife, but the process is pret­ty much the same, start­ing at the heel and mov­ing towards the point, and the direc­tion of the grind is always towards the knife, not away from it, because you’re try­ing to take met­al off the blade.

Here’s what my knife looks like after using the medi­um (280 grit) stone:

Here’s what it looks like after using the 2nd (600 grit) stone:

And here’s what it looks like after using the 3rd (1000 grit) stone:

The bumps and grooves are a lot small­er, aren’t they? And the edge is pret­ty straight, too.

If I had fin­er grit stones, I could take it down to almost a mir­ror fin­ish, but I find that a 1000 grit stone is sharp enough for me.

If you’re patient enough, you can take almost any knife and give it a new edge. If the knife has big nicks in it, you can build a whole new edge, but it’ll take you an hour or longer to do it right. You can also use a pro­fes­sion­al knife sharp­en­ing ser­vice, if you’re for­tu­nate enough to have a good one in your city.

One final note on photography:

The first two pic­tures were tak­en with a Canon T6i cam­era, the first with a 55 mm lens and the sec­ond with 14 diopters of macro fil­ters added.

The pho­tomi­cro­graphs were tak­en with a Cele­stron Hand­held Dig­i­tal Microscope.

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Published:July 16, 2016


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    Mike Nolan

      Take your best knife out and look at it closely.  How sharp is it? Probably not as sharp as you think it is. Here's one of my favorite knives, a Chinese cleaver: Looks pretty sharp, eh? Let's look at
      [See the full post at: The Cutting Edge or How Sharp is your Knife?]

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        My husband uses an electric sharpener on our knives. Don't know the brand, but it was recommended by ATK, as I recall.

        I have my dad's manual knife sharpening stone. Sometimes I want a knife a little sharper than the electric sharpener makes it. Then I use my dad's stone. Many times he gave me oral instructions on how to sharpen knives while he was working with the stone.

        • This reply was modified 7 years, 11 months ago by Italiancook.
        Mike Nolan

          A few years back I was in a cooking store in Pittsburgh and one of the knife makers had a rep there using an electric sharpener, but I don't think they were trying to sell the sharpener, it was rather like taking a knife to a sharpening service, except that it was free. I asked the guy about using a set of whetstones, he said that they're the best way to keep a knife sharp if it doesn't really need a whole new edge.

          Not all electric sharpeners work the same way, some are little more than grinding wheels, so basically what they do is build a new edge. If you know what you're doing (and especially what the sharpener is doing) they're good, but I don't think they put as fine an edge on a knife as a series of fine grit stones can. A friend of mine has some $500 knives, I'm going to be seeing him in a few weeks and I'm going to take my digital microscope along so he can see what his knives really look like.

          My biggest concern with using them is that they can take off too much metal each time. Unless you use your knives for hours every day, they shouldn't need a serious sharpening more than once every few years.

          As I was working on my sharpening post, I spent several days sharpening various knives in my kitchen, including a good meat knife that I hadn't used much lately. Now it works very well, better than my santoku knives for trimming beef. I buy large cuts of meat (almost sub-primals) and trim them down, I get better steaks, roasts and stir fry beef that way and the trim I can't cook with goes in the freezer for the next time I make beef stock.

          • This reply was modified 7 years, 11 months ago by htfoot.
          • This reply was modified 7 years, 11 months ago by htfoot.
          • This reply was modified 7 years, 11 months ago by htfoot.

            Hi I'm back! My favorite knife is a Chinese Cleaver too. I need to sharpen it and my other knives soon. I've been using Accusharp to touch up the edges but the knives are at a point where I need to start with a Medium Grit water stone and work up to fairly fine.

            Mike Nolan

              I was hoping to get some good microphotographs of what impact a sharpening steel and an Accusharp V sharpener have on a knife edge, but most of my knives are pretty sharp at the moment from my work on the 'how sharp' post. So this might have to wait a few months for a follow-up post.

              I've been checking other sites that talk about using a sharpening steel, though, and they seem to be split about 50-50 as to whether the steel should move in the direction from the edge to the spine or from the spine to the edge. Might be a good follow-up post here, too.

              • This reply was modified 7 years, 11 months ago by htfoot.
              • This reply was modified 7 years, 11 months ago by htfoot.
              Mike Nolan

                Two weeks ago a friend brought over a couple of his knives, including a very expensive Shun knife, and we put them under the microscope.

                He thought they were sharp, but at 150X we could see multiple issues with them, including several nicks. I think he may take them to a shop to be reground to a new edge, and he's thinking seriously about ordering a handheld digital microscope like my Celestron. (Meanwhile, I'm thinking of ordering a trinocular lab microscope capable of going to at least 1000X and hooking it to my Canon digital camera.)

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