Chris Schwarz's Blog

Sharpening: The Lies of the Eyes

Isshi Yamada never said much to me when I was dating his daughter in college. To us Western students who studied Eastern religions, he was an enigmatic Zen Buddhism professor who was famous for giving exams that bordered on the surreal.

Most of my memories of Dr. Yamada put him sitting at his dining room table in a worn Irish fisherman’s sweater , drinking a little sake and watching the affairs of the household.

One day, however, Dr. Yamada became quite animated on the topic of human perception. And his short lecture sticks with me to this day.

“What is the one thing the eye cannot see?” Dr. Yamada asked.

I’d played this game with fellow students before, so I jumped in. “That which is too small or too large to see,” I responded.

Dr. Yamada shook his head.

“What is the one thing that fire cannot burn?” he asked.

Like most Westerners, I started to go literal. “Titanium?” I said (or something equally stupid).

“What is the one thing that the finger cannot touch?” he asked.

I shook my head.

“The eye cannot see the eye. The fire cannot burn the fire. The finger cannot touch the finger,” he said.

This short condemnation of self-analysis and self-perception has colored my thoughts every moment since that day. Including today.

As I’ve said before, I do a lot of sharpening. I sharpen things almost every day. I think nothing of the process. I don’t obsess about it. I don’t blog much about it (there is no “Sharpening” category for this blog). For me it is like religion. Not the fervent kind with snakes and faith-healing and fried chicken. The kind that simply flows through everything. Without it, things wouldn’t exist. Without sharpening, woodworking wouldn’t exist. Period.

And I don’t talk about sharpening much on this blog because people get upset. And you should never ever get upset about sharpening. That spoils your efforts.

Like today.

I have a theory. Maybe it’s more accurate to say I had one. Here it goes:

When I sharpen with waterstones, I get the best results if I use firm pressure when beginning with a new grit then I use gradually decreasing pressure on that new grit. This change in downward pressure seems to speed the polishing process, or at the very least it polishes the areas around the deeper scratches, revealing them to my blind eyes.

My crackpot theory: The firm pressure breaks up the waterstone and those particles get smashed into smaller particles on the surface. The lighter pressure I use at the end of a grit allows those smaller particles a chance to work the steel.

Bottom line: Using less pressure will speed your efforts.

So I sent my theory to Ron Hock, the founder of Hock Tools and the author of one of the books we publish that I am most proud of, “The Perfect Edge.” Ron (or the Rev. Ron as he is sometimes called), thought about it for a bit and replied:

“I think your theory is working as well as this one: Assume the grit’s grains are conical with the points standing up. More pressure would push the cone deeper into the steel creating a wider, deeper scratch. Less pressure would skid the blade along only the smallest part of the cone, hence a narrow, shallow scratch.

“I think mine is the simpler theory so, according to the principal of Occam’s Razor, I’m right. (But I think you’re right, too: That due to the crushing action you are loading the surface with finer and finer grit grains and reducing the pressure allows the blade to float on them.)”

So that’s the set-up , not the real story. I have spent the last 17 years of my life sharpening and dulling steel edges, and that is my honest perception. When I use firm pressure I can get my edges only so polished. Then they stop looking better , no matter how much I work. But if I start using lighter pressure, they look better on that same grit.

So I set out on Monday to show this through photographs using our nice macro lens. I sharpened an A2 iron on my #1,000-grit stone until it stopped improving using firm downward pressure. I took its photo. Then I switched to delicate pressure on the same grit. It looked a lot more polished. I took its picture using the exact same camera position, iron position, light position and camera settings.

When I looked at the photos on the computer in Photoshop, they looked identical. I couldn’t tell the difference between the photos with light pressure and heavy pressure. I tried again. And again. I tried for three hours on Monday to capture what my eyes were seeing without resorting to any tricks of light or Photoshop.

No dice.

And that’s where I am today. Perception has failed me completely and I do not know which is lying to me , my eyes or the camera’s resolution (which is poorer than even my eyes).

And so I’ll simply move forward on faith with my sharpening. And the religion simile continues to hold its ground.

– Christopher Schwarz

Do You Dare Read More on Sharpening?

– Honestly: Ron Hock’s book on sharpening, “The Perfect Edge,” is a great reference for woodworkers. Whether you are a new woodworker or a die-hard sharpener, Ron has a lot to share. I learned a good deal from the book, and I’m no sharpening slouch. It’s available from our bookstore.

– Brent Beach’s sharpening site is ideal for someone who wants to take a deep dive into sandpaper sharpening especially. His sharpening jig and abrasive recommendations are without peer. Check it out.

– Who makes the best honing guide for chisels? Richard Kell. End of story. Buy them direct from Richard here. (And buy a sundial while you are at it.)

29 thoughts on “Sharpening: The Lies of the Eyes


    Looks like a 50mm F2.5 compact macro that gives you 1:2 magnification on a full frame camera, so that would be 1:1.25 on a 1.6 crop sensor camera like the 10D.
    You can get sub-pixel resolution via interpolation in combination with other image enhancement techniques.
    Photoshop is probably not the best tool for that, industrial machine vision programs are designed for that purpose. AFIK Cognex/DVT used to have a free program on their website that should be very useful in measuring (as opposed to eyeballing) the wear bevel on woodworking tools.

    Chris Scholz

  2. Brian


    While we are waiting for Popular Woodworking to buy you an electron microscope, let me pose a test that is simpler and probably more meaningful. The test is that the sharpest edge is the one that will produce the thinnest shaving without tears.

    You will need to use a plane that fits the blade snugly from side to side so that once the plane is set up the blade can be removed and reinserted at exactly the same angle.

    Sharpen your plane blade as best you can with heavy hand pressure, install it in a good plane set for a fine shaving, and test the blade on a piece of very straight-grained fine-grained wood, backing off the blade and taking finer cuts until the imperfections in the edge start making small tears in the shaving. With a micrometer, measure the thickness of the finest shaving before tearing appears.

    Resharpen the blade with your lightest final strokes. Reinstall the blade in the same plane changing none of the settings except for the depth of cut. Again start with a fine cut and keep backing off the blade for finer shavings, repeating the previous test.

    Compare the thicknesses of the finest shaving you can get without tearing from each method of sharpening.

    I am assuming that with a really fine grained, straight grained wood (perhaps apple or boxwood?) the first tiny tears that appear in the thinnest shavings will be artefacts caused by micro-nicks or micro-bumps in the edge of the blade. If you are being really fussy, try repeating the experiment by planing a block of paraffin wax without air bubbles, making the same observations. I also assume that any difference in sharpening technique that does not produce a difference in the shaving is between you and your Zen master.

    When I was a student I worked as a histology technician making microscope slides. We would take a piece of a human or animal tissue, embed it in a small block of paraffin wax, and slice it in a microtome, a machine that worked like a very precise baloney slicer, then mount each slice or section on a glass slide. Our sections were typically about 5-10 microns or 5-10 one thousandths of a millimetre thick, depending on the kind of tissue. Although there were electron microscopes in the building, our test of unsharpness in the cutting edge was the first appearance of tears or artefacts in the sections.

    Is this latest obsession part of the rehab to ease you through workbench withdrawal?

    What does Adam Cherubini have to say about all this?


  3. Luke Townsley

    Interesting article. Perhaps you are right here.

    Perhaps the science of small time woodworking is more about psychology than it is about the more measurable and quantifiable sciences. Or as you put it, religion.

    I think you could make a reasonable argument that how sharp you perceive the blade to be affects how you cut with it which is really what you are trying to accomplish anyway…

  4. Christopher Schwarz

    Of course I use fine grits. I’m only talking about the evolution of the surface during my time on one grit.

    And I wouldn’t call it a strange theory. Frank Klausz talks about this same property in his DVD “Hand Tools.”

  5. Edawrd Weber

    When uning an abrasive to sharpen or sand something we traditionally start with a coarse grit and move toward a finer grit.
    Your strange theory about changing the amount of pressure goes something like this.
    If you sand something with 120 grit paper, then you find it’s not as smooth as you wanted it, you return to the 120 grit paper, only this time you don’t apply as much pressure.
    It’s the abrasive that determines the type of edge you get, not the pressure. Adding more pressure than needed is simply wasted effort.
    If you want a finer edge, use a finer grit.

  6. Mark Dennen

    I have been to Lie Nielson in Maine and had excellent instruction in how to sharpen planing knives. The only thing better than their instruction is the quality of their tools.

    I also had the opportunity to observe, on numerous occasions, Bob Ratchford sharpen tools in his shop in Oxford CT. On one occasion, sharpening my kitchen knives, he pushed the blade in to a vertical sanding belt (I thought he would cut the belt, but this was not his first rodeo). He then moved over to his stone which he pre-wet with a kerosene laden brush. He pulled the blade across the stone several times on each side, adjusting his wrist slightly at the end to accommodate the tip. He then moved on to an old radial arm saw equipped with a buffing wheel. Finished, he picked up a newspaper, folded it in half and holding the knife by the very end of the handle, let it fall and it fell right through the folded newspaper. He said to me, "I think it’s sharp." (He charged $1/knife!).

    I spent many an hour with Bob and although he is now gone, one never forgets such sharpening skill.

    Mark Dennen

  7. Sharon Lev

    Chris – a Digital camera, as good as they seem these days is still no match for film in terms of resolution and precision – much like a planer and a tuned #4.

    As a general rule – pictures that come out of a digital camera ALWAYS need sharpening – and yet still will never get to the accuracy of film. although for the human eye, for most situations this is more than good enough. but for what you are trying to find, a 10D may not be the best tool for the job.


    Scanning electron microscopes don’t go up to 500,000x. That requires a Transmission Electron Microscope (TEM) and a special sort of sample that’s been thinned to microns thickness. And you don’t need more than 1000x or so — your field of view at 1000x is 5 mils for a 5-inch wide photo.

    The big reason to use an SEM is that it has incredible depth of field — the whole sharpened edge will be visible. With an optical microscope, any image over 200x or so is going to be of a flat surface (polished and/or etched). That’s why we frequently used an SEM for photographing fractures, even if we didn’t go above 200-500x.

  9. Rob

    Very interesting and entertaining post, as always.
    Can you show the relevant photos from your different techniques of sharpening? Have you compared wood surfaces cut by blades using the different techniques – to see if this amounts to a hill of beans in this crazy world?

  10. Matt

    Do not try and bend the spoon. That’s impossible. Instead… only try to realize the truth.

    There is no spoon.


  11. Steve

    I think Stuart may have hit on something significant: Honing (grinding an object against a solid abrasive) and lapping (grinding two objects against each other, with an abrasive grit suspended between them) produce different kinds of scratch patterns. Although neither is necessarily better than the other, they can look very different.

    When you’re pressing firmly on the tool, you squeeze out most of the slurry, and so it’s more honing than lapping; when you lighten up, the slurry does the work, and it’s more like lapping.

    If you’ve purchased a plane blade from Lee Valley within the last few years, you know what I mean: The blades are lapped on the back, and have a dull, matte surface. This is very different from the reflective surface that we usually end up when we hone the back with a sharpening stone.

  12. Mitchell

    Hey Chris, it might be your eyes, it might be the camera’s resolution, but I bet it has more to do with the calibration of your monitor.

  13. Ron

    I agree with what Steve said.

    But you may be able to devise an experiment that gives you a quantitative answer. Use a pendelum, make the blade parallel to the swing and using the same counter weight and starting from the same height allow the blade to swing into something easily cut. Like the top of a phone book. Sliding the phonebook sideways would expose fresh target, do say five to ten swings be sharpening method and measure how far the blade cuts.

    You would have to set it up so that the phonebook is high enough to stop the swing before it hit 90 degrees (I think, it would have to be worked out).

    I’m assuming sharper blades would have less friction and would swing further before stopping. Cheaper than electron microscopes anyway.

  14. Damien

    I think ending with less pressure is a good idea, whatever the material is. To quote John Juranitch: "The last few strokes on the fine abrasive (dry oilstone) should be just the weight of the knive." The Razor Edge Book of Sharpening, 1985

  15. Dean


    You might want to try what Brent Beach did (off of his web page that you provided) –

    You can pick up the improved version of the Intel QX3 here (QX5) –

    Oh, and the QX5 is much cheaper than a scanning electron microscope. However you can pick up a nice used SEM here for only $135,000 –

  16. Sean

    "Sadly, we’re the only woodworking shop without an electron microscope!

    Does Grizzly make one?"

    Try Harbor Freight.

  17. Stuart


    Not like I am expert here or anything, but there is, I think, a little more going on here than simply ‘smashing grit’.

    They key point here is that the stone is made up of abrasive AND a binder. Two stones with identical abrasive, but with a different binder/glue will behave vastly differently. Change the abrasive, yet keep the same binder, and again you get stones that behave very differently.

    So great pressure may well be breaking away a lot of ‘stone’, creating plenty of slurry, but the slurry is filled with hard, durable abrasive so it’s really no different to what’s still held tight by the binder, except that it’s now rolling around and doing less work than it would if it had a nice, stable place to sit.

    Now, take a few different stones, use them and the differences become glaringly obvious very quickly, no digital gimmickry required. The type of steel being sharpened has a role to play in the puzzle as well. I find that any given stone tends to behave in pretty much the same exact way no matter what you do with it. Maybe changing the pressure affects the end result in some small way, but not as much as leaving the stone to clog up, or even washing away the spent grit.

    A waterstone is not a high tech piece of gear, being little more than a glorified and occasionally colourful brick, but like house bricks, there is more than one way to make the things, and the end product will be very different, even though the basic ingredients are pretty much the same.

    Oh, what cannot be seen, burned or touched?

    Nothing. But once nothing is identified, it then becomes something…

  18. Christopher Schwarz

    Sadly, we’re the only woodworking shop without an electron microscope!

    Does Grizzly make one?


  19. Plane Noob

    Was "honest perception" intended to be a pun?

    Also, don’t you have an electron microscope handy?

  20. Lloyd

    To get a good image, you may want to try a Scanning Electron Microscope (SEM), like Ron did in his book. Most University should have several different types. They run ~$50 per hour for researchers in the University, and ~$250 per hour for outsiders. Especially with a metallic sample, you should have no problem getting 500,000X magnification.


  21. Steve

    Strictly speaking, your (as well as Ron’s) idea is a hypothesis, not a theory (that is, the idea has been proposed, but not yet tested). Only after a hypothesis’s predictions have been tested and confirmed does it get to be called a theory. You were on your way towards that end with your experiments with the camera, but since the prediction (that the results would look different) didn’t come to pass, the idea is still just a hypothesis.

    By the way, I wouldn’t have expected the difference to show up with an ordinary macro lens. Here’s why: The detector in a Canon Eos 10D has pixels that are approximately 7.4 micrometres on a side. I can’t tell from the photo what kind of macro lens you’re using, but most macro lenses don’t go beyond about 1:1 magnification. That means that, at best, the resolution of the images you get from that camera setup is going to be 7.4 micrometres. From a sharpening standpoint, that’s pretty coarse (in the vicinity of a 2000-grit waterstone). You need substantially higher magnification to be able to see the same kind of detail with the camera that you can with your eyes and a simple 10X handheld lens.

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