Sharpening Stones – Watch Out for the Bumps…

For more information on sharpening stones, see our beginner site Common Woodworking.

…Hollows, Blind Curves and Pits

After the recent posts on sharpening, the first one really, I received comments and emails from people stating that the reason the stones were concave was because they were used for knife sharpening and not sharpening planes and chisels and such. That’s occasionally the case but the ones I am showing and referring to are sharpening stones used by woodworking craftsmen. I have seen and used stones just like these so my answer to this is short enough. It’s simple to tell the difference because of sawdust in the gaps and cracks and mixed with oil it’s pretty conclusive, but beyond that there are pressures and wear areas on the stones and the boxes that determine the reality too. Rest assured, across past millennia, honing stones have been eroded into concaved surfaces along their length by woodworkers of every kind. Most of them remained concave and were never ever flattened. Craftsmen kept them concaved and matched to their personal body movement merely as a matter of course. Why? Because flat stones are not so essential as people now believe. DSC_0007

Concave and hollow —

Are we discussing two different conditions or one and the same?

My quest to fill in the gaps of time between accountable hardware stores on main streets selling domestically made goods on a local level and catalog companies with delivery to the door I think may fall on stoney deaf ears, be subject to criticism or worse still be subjected to opinions that are little more than that, but I am hoping mostly not. You see, sharpening became intrinsic to me in my work and I ‘feel’ for the actual edges I want for each tool, which means I sharpen the edges to task and they are therefore not always the same edge. P1010226 That’s the benefit of mastering freeform sharpening — freedom of choice. Where honing guides do create the same edge every time, I require differences for my work and one day you too may want a few differences to your cutting bevels and edges too. An example of this is steeper bevels with a convex that is more a blunter elliptical shape, or a shallower paring angle for hand pressure only. Instead of a rigidly fixed bevel for say a bevel-up plane iron I might want two extra swipes to increase the bevel 5 or 10 degrees for a particular grain or even a single stroke on the large flat face of a bevel-down plane to create a poor man’s ‘York’ pitch to deal with a patch of wild and awkward grain using either plane type. Mostly it’s all about a ‘flex’ I don’t get without freehand sharpening and it’s what we craftsmen do but don’t write about ‘cos we’re working and making and doing without necessarily trying to teach or even ask ourselves, “Now why did I just do that?”, so we can indeed pass it on. You see, as I’m working I ask myself these questions and then I investigate something I just do and take for granted so I can make sure what I’ve learned gets to other people, woodworkers, so it doesn’t die with me.

The stone’s shape need not be flat but it can be too.

P1010208 Is that dissidence in today’s age of advanced technical knowledge and superiority and the ever-advancing age of “The Opinion” or worse still “IMHO”? Looking back through the last half a century and more in which I lived it does seem to me that a development occurred in the 1980’s that really didn’t exist before and that development just about affected the whole world of woodworking  sharpening unquestioningly. One, everyone and their dog began buying Japanese water stones rather than oilstones and two, everyone became obsessive about spending gobs of time flattening them and I do mean obsessively  beyond question. A third dimension quickly happened unquestioningly and that was the abrasive giants saw that they could no longer live on their past complacencies. Western abrasive companies were indeed losing ground fast and could no longer sell their ‘old fashioned’ sharpening stones even though they actually worked just fine. The woodworking populace, and I mean the new home woodworker who worked wood for leisure and pleasure and not for profit, having little to base their experience on since the demise of men working with their hands was all but gone, was looking for answers to sharpening they could not garner from experienced workmen as they might in times past. It seemed that every magazine started featuring articles every few weeks on the newer Japanese water stones and suddenly the giant abraders of the industrial world had to break through with ever newer versions by creating their own versions of the Japanese stones. Hence the presence of friable stones that surface fracture so rapidly they need constant flattening and, get this, getting people to spend more time flattening than sharpening and more time doing both than they do actually working wood. You see water stones do indeed cut steel fast but they also wear super fast too. It’s a perfect symbiosis between manufacturer and seller. First create a perceived need and then come up with an answer. Consumerism perfected. Wear is wanted and so too is flattening and flattening stones and metal flattening blocks and additional equipment not the least of which is water baths and rotating stone carriers and so on. Try explaining all of this in a sharpening class and all of a sudden you, the teacher, are as confused as those trying to learn from you. Simply put, all you need is some kind of sharpening stone coarse enough to establish, restore or maintain a bevel, a medium stone to refine the coarser abrasions and then a finer stone to polish out the bevel. After that a strop of leather and some buffing compound and your on your way to arm shaving hairs.

Back to the question do stones need to be flat?

Generally no, but there are conditions here not the least of which is  the fact that the condition of stones often varies quite drastically and even hollow stones that look the same are most often different. the stones are incidentally and shaped by the man to the man actually using the stones. In other words the arm/hand/upper body action coordinates  differently with every person and this depends on many things including experience of the user, height in relation to bench, hand positioning and many more issues. How irons are presented to stones, that is presentation angles and such, creates a shape over time to the surface of the stone and almost always creates a hollow or concave. That is unless you are indeed experienced. These hollows and concaved surfaces then are a like a fingerprint to the worker using his and her sharpening stones. The hollows are all different and never quite the same. That’s why, unless you use diamond plates or dead flat surfaces, most non-casual woodworkers feel awkward suing someone else’s concaved sharpening stone.

Hollows, concaves or merely curves

Whereas we often see sharpening stones as merely more curved than hollow in reality, most whetstones are in fact dished with a formed hollow concave. We do indeed tend to use the terms hollow and concave interchangeably and though these are indeed generally the same condition, that is ‘dished’, the terms tend to describe something curved in two directions rather than curved in one direction only. The reality is that sharpening stones (as distinct from diamond plates that stay flat) naturally crumble throughout the process of sharpening.


This hollowed stone shows the oil gathered in the hollow after sharpening freehand

The results of such eroding is an uneven hollow in that a deep curve occurs along the length of the stone and then also a slighter curve across the narrower width  though this is generally less detectable by eye but still present. I have generally found dished stones that dish in varying degrees and the comparisons show that no two stones are indeed alike.


In the case of this stone the long hollow is 1/4” and 1/32” across the width. Sharpening on this particular stone creates a curved and cambered shape to the bevel of the cutting iron; the kind you might prefer for a gentler scrub plane iron. At the bench we might generally prefer a single directional curve along the length only and to avoid dishing as such. This is what I learned as a young man from the men I worked with. This has always been achievable intuitively and that’s how I managed to maintain the single curve in my stone surface for three decades. You see everyone selling stones and those having sharpened for only say a few years and periodically at that, see only one perspective and fail to consider the developed skill of the craftsman using the stones and the tools. Remember that I sharpen my tools throughout the day many times and have done so for the past 50 years. When we sharpen on honing stones we do not simply shove the irons and chisels back and forth in a machine-like movement but we flex the tool edges, the hands, the wrist the arms and the upper body to manipulate the tool’s edge to achieve specific results in forming a cutting edge. In the same long motions, instead of purely long mechanical strokes back and forth and parallel to the sides of the stone we often use elongated oval  motions where the iron of wider blades like wide chisels and plane irons actually overhang the long edges. (Please remember that sharpening stones, especially natural ones, were rarely wider than 2” and irons were almost always wider, 2 – 2 1/2” wide,) so the irons were always skewed to the stones, never held in a honing guide and still hung over the edges of the stone even then. It’s by using long oval motions that we manage to keep to a single curve along the surface rather than actually ‘dishing’ the stone and creating a concaved hollow. How to pass this on is difficult, but I know at least for all of the stones I’ve worn through over the years they have always been flat across and curved evenly along the length. I survived with curved stone surfaces for three decades that way and never flattened the stones throughout those many years.

The jury is indeed still out though

The fact is that you really do not have to have flat stones or maintain flat stones and I hope to get to more detail on this in my next sharpening blog, which I think will show what really matters.


  1. Two questions that may be one: How do you sharpen an edge wider than your stone (I know you eluded to this, but I was hoping you could elaborate)? How do you sharpern an edge narrower than your stone without cupping your stone?

    Thanks in advance

    1. So, definitely not an experienced user, but here’s how I have done it. Hold the iron 45 degrees to the length of the stone, then tip it to your desired angle for the bevel (say 30 degrees), and do your sharpening. This means one corner of your iron will be in front of the other. You’ll need to still push straight down the stone. Look up how Paul raises a panel with his plane. The position of your iron on the stone will be skewed like his plane is for doing the end grain on those.

  2. Thanks Paul,

    You are often the contrarian from what is often presented but it helps me in all the confusion. What is natural for you with 50 years of repetitive practice is frustrating for me as a half time wood worker trying to get a handle on his hand tools. LOL!

  3. I’ve always assumed the curvature along the length of the stone was in part a result of not being able to start the sharpening edge of a tool directly on the front edge of the stone and finish exactly at the far end of the stone. The tendency then to try and stay within the stone’s face and not go off the edges mistakenly. Thus creating the most wear in the middle section of the stone.

    A short video depicting how you sharpen on a curved stone Paul might prove illustrative to those who can’t visualize from the text.

  4. Those who advocate Japanese water stones also advocate keeping them flat by rubbing on other stones. Are you saying that these could be allowed to develop a natural hollow with freehand sharpening? How do the Japanese use them? just curiosity as I use diamond plates which of course remain flat, but I still see others promoting Japanese water stones as producing the keenest edge.

    1. Once the back (large flat face) is flat and polished out you need never flatten those faces again and by that I mean flatten on the coarse stone and follow through on ever diminishing grit grades to a polished face, again. It’s a done deal. All you need after that is the bevel honing and the only reason we do this face is because it’s a fraction of the size of the large one and you can indeed bear down on the bevel because of the angle of presentation. This then gets you to the broken and worn edge fastest. As you move along to the finest polish the burr drops off and the tool is ready to go. You do not need a flat face for the bevel at all. All I ask is that people try it. How come I never now work on the large flat face and yet I get the results that at the very least parallel all other methods?

    2. David,

      the keenest edge part may simply be because they went to a higher grit on the Japanese stones. My father-in-law (now retired Japanese carpenter) never bothered keeping the stones dead flat or polishing the entire bevel… he was trained in the trade by his own father-in-law, who apprenticed before WW2.

      I use DMT (200 to 1200), man-made oil stones and natural whetstones. I am very lucky for the natural stones as a lot of the hones historically used in Solingen’s razor sharpening workshops were quarried just outside my town… so I can basically pick great quality whetstones for free just by walking around the countryside. The highest grit stone I found to date is a local slate that goes up to 8K depending on the level of slurry you raise on it… it’s close to the Welsh Dragon Tongue (quarried a bit south from Paul’s workshop) except a faster cutter.

      I normally perform the heavy repairs on the DMTs then progress to a CrO strop (chopping chisels, turning tools) or oil/water stones (paring chisels, planes, gouges). For the really hard steels or larger chips, I have a hand-cranked grinder. It is a very fast setup… I normally go from “flea market special” to usable tool in 5 minutes. I’m also using the same hones for my straight razors…

      1. Excellent answer, Michael. Combining that with Pauls essay, I think the answer is that any method can work with sufficient time, experience, practice. and …… mentoring. The trouble is that most us do not have enough of any of these. Hence the ‘snake oil’ salesmen who, to give them their due are trying to find methods that get an amateur quickly to at least 80% of what the professionals can get to. So there is no short cut to getting that last 20%, which is probably only needed for difficult work or a very fine finish. So thanks, I will stick with the diamond stones/strop that Paul has introduced and work out how to continually improve. Paul, can I throw a final question at you. Are you aware of what is taught in our schools today? That is really where it should all come from.

        1. David,

          I forgot one detail which may be important: my father-in-law was sharpening on Japanese natural water stones.

          You’re spot-on with “practice and mentoring”… you’ll progress faster if someone can show you the basics.

  5. I don’t no Sellers am kind of loosing the point on this flat hollow stone fact finding none bias study. The Japanese make some pretty good stones, I’ve seen you raise some sparks with the three diamond plates on you tube and the Windex (aka glass cleaner). I like the Diamond Plates but my Japanese stones are pretty sweat. I have the really good ones very solid and they cut fast. No doubt you can get a sharp edge of them oil stones, I hope. Sometimes I don’t want to deal with water and the cleaning after I sharpen so I stay with the diamond plates. But I can use my diamond plates together with the water stones and they make a good combination. If I was to sharp that many times a day I would have to factor that into my operating cost together with the windex and my dogs water stone set as well, (that sucker has never earned a dime in his life). Question if a hollow stone is the ideal why sell flat stones. I have two books on sharpening one from Leonard Lee and the other from Ron Hock not to mention that almost every woodworking book discusses sharpening. Theres a section that recommends Flat stone’s as the ideal and it goes on with convexity and concavity and how that gets transfer to the blade including the edges will round up. This is ok for plane blades but not for chisels they should be square through out. It discusses how different grits will wear at a different pace, when you go to a higher grit the blade will sit differently because the stones wear out at different rates. Now I don’t have to worry about that if my stone is flat thats simple enough at least for me. I have another book by Garrett Hack “The Handplane Book” he has a section on sharpening page 62 he wrote “If you ever want to get a heated discussion going among woodworkers just mention sharpening. Everyone has an opinion on water stones versus oil stones, hollow grinding, micro bevels, and every aspect of sharpening technique. To some it almost borders on religion. So I’ll jump into the fray with my opinions.”

    1. I wrote exactly the same as they did until a few years ago when I realised that the only reason I might need the flat face is for doing something to the flat face I never really need to do once it’s flattened and polished out. All I am saying is a continuous convex bevel cuts exactly the same as a micro bevel edge if both edges are polished out equally from cutting edge to the opposite side of the bevel. One matches the other. If that is so, why not simply let the stones go hollow instead of going through the ritual of reflattening what does not need reflattening. You can still put a secondary micro bevel on an edge on a curved stone as well if you insist on the obsessing, but imagine never needing to flatten again. Beyond that, why not just keep the opposite side of the stone flat for flattening if you want to? Then you have the best of both worlds though it is generally unnecessary it’s handy to have access to a flat stone I suppose.

  6. Did the ‘old timers’ maintain a set of flat stones that were only used for the back side of chisels and irons?

    When I get a new tool I flatten the first 1/2″ or so. Over time, as the edge is worn, the back side will have to be maintained with a set of flat stones.

    What’s your recollection from the past?

  7. Well Paul, when did you switch from hollow oilstones to flat diamond plates, and why please?

    Also how did you deal with the wire edge?

    1. Two good questions. I first used diamond plates 20 years ago. For many years I never knew anyone that used them in woodworking as most new woodworkers were being introduced to using waterstones and craftsmen were still using mostly oilstones. It seems obvious that they saw no need to change because sharpening was then what it is today, no more than a two minute necessity frequently turned to throughout each day.

      I actually didn’t altogether stop using oilstones at first but continued using oilstones and diamond plate in tandem with one another. In those days I found people were using diamond plates to flatten stones and so asked myself the question why not just use diamonds. Now I use diamond plates but not everyone can afford a £140 set up starting out. My raising this issue in these last posts has been to show that many woodworkers did camber their irons along the cutting edge and also didn’t necessarily flatten curved stones because it’s not always essential. That said, I prefer flat plates because they are more useful that way. I can create straight, cambered and curved bevels and edges easily on flat plates and so I use these as my preference. They also last well. I think were I a lone craftsman as I am still and working full time, using these stones only they would last me ten years.
      As to hollow stones; I made the distinction between hollow stones and curved stones early on in the articles because they are distinctly different. One is not really a problem and the other is or can be. It’s my argument that once the large flat face of any blade or chisel is flattened and polished out, it’s rarely necessary to revisit that surface for anything more than light polishing and indeed to remove any residue of a burr. I use a leather strop for most of my bevel polishing and take the bevels to 15,000. Stropping at the same angle as honing alone removes almost all residue of any burr. For polishing out the flat face, should that be necessary at any time, I use a flattened piece of hard maple charged with buffing compound for any finalising to the flat face.

  8. Thank you for your writings here. More a memory from my hands than from the brain occurred in the reading. I got my first sharpening stone at around age 6 from my grandfather. A course side and smooth side, Learned to sharpen while sitting on the grass of a bank under a large cedar tree in his yard. After getting coordinated to the feel of the blade in one hand and the stone in the other, yes no benches or holders or guides other than my fingers, i got it! On occasion I would by “Allowed” to use my grandfathers stone more curiosity than cause. He is so amazingly good it must be a better stone! Right? I still remember him laughing at me and saying that i couldn’t use it. I found it completely uncoordinated and foreign object in my hand and proceeded to quickly foul my edge. He laughed more and it was greatly funny for us both! The shape truly becomes the fingerprint of the man. Thank you for your thoughts and writings here and everywhere else as well! I just smelled the cedar tree and the grass where we were sitting and felt the grass on my bare feet again. That was 48 years ago. Thank you

  9. A few years ago I thew out my oilstones because they weren’t flat. The unflatness was worsened by using a honing guide.

    I wish that I had been trained to sharpen properly. I learnt in the 70s and 80s at school. A workshop were we were always told to lay planes on their sides.


Comments are closed.

Privacy Notice

You must enter certain information to submit the form on this page. We take the handling of personal information seriously and appreciate your trust in us. Our Privacy Policy sets out important information about us and how we use and protect your personal data and it also explains your legal rights in respect of it. Please click here to read it before you provide any information on this form.