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

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