Advice is a dangerous gift, even from the wise to the wise, and all courses may run ill.
We receive a lot of enquiries about natural finishing stones, so I wanted to share some of my thoughts and experiences about them with you. Perhaps they will be useful.
To begin with, natural Japanese stones are a lot of fun, and can create a beautiful, cloudy finish on a blade’s bevel. They make my heart sing, wild thing.
I think blades finished with a natural stone tend to stay sharper a little longer compared to synthetic stones, but can’t prove it. Despite my fondness for them, I want to make it clear that natural stones are not magic, and are not critical to do good work.
It is interesting to note, however, that while top-quality natural stones are expensive, if judged by the amount of steel they can sharpen, they are actually no more costly than the better synthetic stones. But they can be more of a gamble.
Geologists believe that Japanese natural sharpening stones were created when particles of volcanic dust fell from the sky, transported, sorted, and sifted by winds and waves, and settled onto the sea floor eventually becoming sedimentary stone.
Being natural, they carry the inherent and potentially expensive risk of internal defects, such as weakness between sedimentation layers, cracks, and contamination such as hard particles of sand concealed inside. Even if you find one that seems perfect in every way, the bones never stop rolling because you never know what lurks inside.
I erred with my first purchase of a natural stone. It was recommended by the hardware store owner in Sendai where I bought it many years ago, and I fear he intentionally foisted a low-quality stone on me that a person more experienced with natural sharpening stones would have rejected. This stone “drags” steel, a phenomenon where the stone deposits hard clumps on the blade that gouge the stone’s surface and leaves rough spots on the blade. It’s impossible, BTW, to judge a stone’s propensity for this pixieish behavior by eyeball alone. I learned an expensive lesson about both natural stones and salesmen that day. I still use that stone for sharpening axes and gardening tools, but the real reason I keep it around is as a reminder of my foolishness.
After that first disastrous purchase, I became more careful and paid less attention to what people said or write. Instead I learned from people’s mistakes. And I considered motives. Consequently, I don’t give a rodent’s ruddy fundament about most people’s opinions. Too many who claim expertise talk and write about things they only partially understand. Many have a conflict of interest. Still others seek justification of their poor decisions.
Nor I do care about the region or mountain or mine a stone came from, or its designation or color. Even the best mine produces mostly waste.
And because of the impossibility of evaluating stones long-distance, and considering Gildor’s wise words quoted at the top of this post, I don’t give advice about stones, so please don’t ask. But I will tell you what I do when buying a stone:
I examine the stone for cracks and signs of irregularities and impending separation at its sides (not all defects are fatal);
I take the stone in my hand, close my eyes, and feel it;
I flip it with my fingertips and listen to the sound it makes;
I touch it to my teeth (the surest way to detect the fineness and consistency of a stone’s abrasive qualities);
I put a plane blade to the stone and take a few strokes, and like a bow on violin strings I feel the friction and listen to the music;
I examine the scratches it leaves on the blade’s jigane and hagane using a loupe.
None of these critical tests can be conducted long-distance. BTW, if you think any of them are pointless, then I know where you can get a good deal on some swamp land in North Korea.
I have two natural stones I use regularly nowadays. One is of medium hardness suitable for most every straight blade. The other (see the picture below) is very soft, and easily damaged, but creates a beautiful foggy finish on the steel.
I love my natural finishing stones, the feel of using them, the smell, and the pretty finish they produce on my blades. They are part of the romance unique to Japanese blades. I believe the stones I use now and their sisters worn to slivers in past decades were worth every penny I paid for them, but I recognize this is an emotional rather than practical viewpoint, and difficult to defend economically.
And just to save you wasting your time with questions, allow me to explain that we don’t sell synthetic sharpening stones because we can’t sell enough to justify procuring enough volume make our prices competitive. Besides, shipping costs would be too high. And we don’t sell natural stones because we cannot provide a warranty on anything so unpredictable, and I really hate disappointing people.
Don’t misunderstand: I am not suggesting you should not try natural sharpening stones, only that you carefully evaluate them in-person beforehand, and buy from a reputable dealer that offers a reliable warranty (please don’t ask for recommendations). And just to prove I am neither troll nor curmudgeon, I will give you the same four points of sound advice about purchasing natural sharpening stones that a wise old man gave me a long time ago, advice that has passed Gildor’s test.
First, don’t trust your eyes alone when judging a stone’s origin, designation, appearance, or performance (see the five tests listed above);
Second, don’t buy a stone from someone you don’t trust and who won’t give you a reliable 30 day warranty. That gives you time to check the stone carefully for suitability and defects. Remember, the combination of stone and blade is much like a marriage where the softer (but actually granularly harder) stone smooths and polishes the harder blade. If the two don’t work well together, then even lawyers can’t make it right, but a warranty may help reduce the damage;
Third, always try a blade on the stone before purchasing it to make sure it works for you and your blade;
And fourth, don’t whine if the stone disappoints: roll the dice and smile at the faces they show you. Besides, hoes, axes, and hedge shears need sharpening love too.
On the other hand, if you can follow the last rule and don’t mind risking your money, then the previous 3 rules can perhaps be ignored. I grew up in Sin City and know that can be fun too. You pays your money and you takes your chances. Viva Las Vegas!
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form located immediately below.
Those who hammer their guns into plows, will plow for those who do not.
Hand forging is an ancient blacksmithing technique that, from the viewpoint of cutting tool performance, has been almost entirely replaced in modern times, but never surpassed. Understanding a little bit about this technique and its history is helpful in understanding what a good blade should be.
Before motor-powered machinery and gas-fired forges, steel was very expensive. It took a lot of expertise, fuel, manpower and endless hammering over long periods of time to turn rocks into useable pieces of steel, an economical reality that shaped civilization for millenia. International economics aside, all steel was of necessity hand-forged back then.
This is not an efficient process compared to drop forging or press shaping. It consumes more time and fuel, and requires more labor, skill and experience. It is contrary to modern mass-production methodology. It’s a job for a trained blacksmith who demands a fair wage, not a seasonal factory worker in Bümfüq Guangzhou intent on earning enough cash to put a new corrugated sheetmetal roof on his family hovel in the countryside.
In the final analysis, hand-forging is both unprofitable for corporations and too expensive for consumers who actively value low cost and appearance above performance. No wonder it’s as Dead as Disco.
You may recall people talking about how they prefer to use hand-forged antique chisels and planes because they are superior. Those old tools certainly don’t look superior to modern tools, and they aren’t cheap. But are they superior? And if so, why?
The essence of hand forging is using hammer, tongs, anvil and forge (charcoal/gas fired) to violently shape the metal during a series of heating and cooling cycles. The combination of hammer impacts and repeated heat cycles (heating, cooling, reheating) breaks the relatively isolated, large clumps of carbide crystals into uncountable small crystals, distributing them more evenly throughout the steel’s matrix, producing the sharper, more durable, and most desirable “fine-grained” steel.
The properties of this steel are what make it valuable.
Let’s examine some of these coveted properties. The first is is that it is tougher than steel of lesser quality, meaning it is less likely to fracture due to crystalline defects. In the case of swords or knives it means the blade can cut and chop without breaking when subjected to stresses that would destroy a blade made of lower-quality steel.
The second and third ways fine-grained steel is superior is related to the first. The consistent crystalline structure with its finer carbide crystals distributed more uniformly throughout the matrix results in a cutting edge that can be made sharper, and that will retain that sharpness longer than steel of lesser quality. Of course, realizing this performance depends on the quality of the materials employed, and the skill and diligence of the blacksmith.
Many antique tools were made during a time when steel was expensive, and hand-forging was the only way to shape it. In fact, in the case of critical tools such as swords, this process included forging and reforging clumps of impure iron, folding and refolding the resulting mass into itself hundreds of times to remove impurities and adjust the carbon content, typically resulting in the a loss of 75+% of the original material’s mass. That’s a lot of material and manpower tossed onto the ash pile.
I call these tools critical not just because of their important functions but because of the implied warranty that went with them. For instance, if such a blade failed in battle, the blacksmith’s implied warranty went beyond financial compensation and involved the loss of his body parts at the hands of his vindictive customer’s surviving family members. How’s that for an “extended warranty?”
But any decent steel cutting tool was time consuming and expensive to produce. Until quite recently, blacksmiths did not have tools such as infrared temperature gauges, oxygen sensors, or hardness testers. All they had were their hands and Mark 1 Eyeball, so it took many years of training under a master for a blacksmith to learn how to make a good blade and survive.
Quality control was a big problem back then, but the blacksmiths in Scheffield, Philly, Solingen, Fukuoka and elsewhere still managed to make excellent blades of all varieties with fine-grain steel as the customer demanded. Most of those surviving blades are superior to what is manufactured in the West today. Certainly better than anything made in Chinese factories.
Unfortunately, it is impossible to judge a piece of steel’s crystalline structure with the naked eye, a fact mass producers exploit nowadays to make huge profits selling low-quality tools made from scrap at relatively high profits based solely on the tool’s appearance as it hangs on the hardware store wall encased in its impermeable armor of clear plastic. Lower-quality tools became widely acceptable once a generation or two of consumers that knew the value of cutting tools hand-forged from high-carbon steel left for the big lumberyard in the sky to be replaced by more urbanized generations that valued low cost and appearance more than performance.
Sadly, while the quality, consistency, and workability of steel as a material has greatly improved, the ancient technique of hand-forging has been abandoned throughout most of the world, skilled blacksmiths are almost extinct, and blade performance has suffered as a direct result.
Hand forging is still practiced by some blacksmiths in Japan, where the greater quality and performance this technique provides are still highly appreciated by craftsman obsessed with performance. Accordingly, our chisel and plane blades are made from modern high-quality high-purity steel produced by Hitachi metals instead of the much more expensive and difficult to work traditional Tamahagane. However, our blacksmiths hand-forge every single blade in their one-man forges through a minimum of three heats to form a fine-grain steel with the characteristics noted above that Japanese professional woodworkers demand.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form located immediately below.
“The true mystery of the world is the visible, not the invisible.”
In this post we will dig into a few important nitty gritty points about sharpening stones everyone needs to know. Perhaps you already know all these points, but please ready your shovel because there may be at least one buried surprise.
A Flea’s-Eye View
When seen under high-magnification, the surface of a sharpening stone looks like millions of densely-packed stones embedded in a flat field. The smaller the stones, the finer the grit.
As the blade is pushed and pulled over these stones, they scratch and tear metal from the blade’s surface leaving behind scratches corresponding to the size of these small stones. This violence continues until the blade’s ura and bevel form a clean intersection of two planes.
Seen under high-magnification, the cutting edge is jagged where these furrow-like scratches terminate at the cutting edge. To some degree, it may even look like a serrated sawblade. Some blades, like kitchen knives and swords, are used in a slicing motion to cut soft materials like meat and vegetables and enemy arms, and their performance benefits from a serrated cutting edge more than a highly-polished edge, and so do not need to be highly polished on fine-grit sharpening stones.
Plane and chisel blades, however, are used to cut wood, a material typically harder than foodstuffs, in a straight-on direction, not in a slicing motion, for the most part. In this situation, a rough, serrated cutting edge is weaker than a highly polished edge because the jagged edges are projecting out into space like the teeth of a handsaw blade, and are relatively unsupported and more easily damaged than a highly-polished blade with smaller, more uniform scratches terminating more cleanly at the cutting edge.
Therefore, in order to produce a sharp durable blade, we must make the microscopic cutting edge smoother and more uniform by using progressively finer grit stones to produce shallower and narrower scratches, and a thin, uniform cutting edge.
But how fine is fine enough? There is a curious phenomenon related to friction that is applicable to cutting edges, and is useful to understand.
The Friction Paradox
Imagine a cube of heavy stone with its downward flat face resting on the level, flat surface of a larger slab of similar stone. Let’s say it takes some specific measure of force pushing horizontally on the stone cube to overcome the static force of friction between the two stone surfaces in order to make the cube start moving.
If we gradually increase the degree of polish between the two contact surfaces and measure the force required to start the cube moving at each progressively higher level of polish, we will find the force decreases with each increment of increased polish, for a time. This is at least partially because the irregularities between the two surfaces (asperities) do not interlock as deeply when the surfaces become more polished.
However, at some point, more polishing brings the surfaces of the two stones into such intimate contact that the molecular attraction between them, and therefore the force necessary to move the cube, actually increases.
The Inflection Point
The same phenomenon occurs with tool blades. If you sharpen and polish your blades past a particular point, the friction and heat produced between blade and wood will increase, as will the energy that must be expended, while the resulting quality of the cut and durability of the cutting edge will not improve significantly. Of course, the time and money invested in stones spent sharpening past this point will be mostly wasted.
The inflection point where additional polishing yields increased friction with little improvement in cut quality will depend on your tool and the wood you are cutting, but you can gain a pretty good idea of where it is if you pay attention over time. While the sharpening stone manufacturers hate my saying it, in my well-informed opinion there is little practical gain, beyond self-satisfaction, to be had from sharpening chisels or planes past 6,000~8,000 grit, making this range of grit an inflection point in my mind. What about you?
I encourage you to conduct your own experiments to determine the inflection point in the case of your planes and wood you cut. Many who figure this out save themselves significant amounts of time and money sharpening over the long-term.
To those of our Gentle Readers that love sharpening more than woodworking, and enjoy putting money in the pockets of sharpening stone manufacturers more than keeping it for themselves, I apologize for pointing out the floater in the punch bowl. But you probably would have it noticed it eventually anyway, if only from the taste difference.
I will touch more on this important point in the next exciting installment in this scientificish adventure.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form below.
Ideally, a tool blade will have absolutely uniform dimensions: the right thickness and taper, perfect cross-sections, uniform curvature, and straight edges and surfaces. However, professional grade Japanese tools are not made on CNC machines, but are hand forged, and have dimensional imperfections. Indeed, imperfections are part and parcel of all human endeavors. Most imperfections don’t matter; Sometimes they make the tool better; Other times they need to be remedied.
You, Gentle Reader, may not notice that the blade or cutting edge of one of your chisels or planes is “skewampus,” and consequently the cutting results are less than ideal. You may blame those poor results on your technique in using the tool or the irregular wood grain, when the real problem is the shape of the blade’s cross-section, or your unintentionally sharpening the blade with a skew. We will examine this problem in this post.
We will also look at the curved or “cambered” cutting edge profile in plane blades, the benefits and undesirable results it can produce, and how to incorporate this blade profile intelligently into your woodworking repertoire.
Many people, like monkeys in trees, learn bad habits from their friends and teachers. We hope this post will help you understand what is going on with your woodworking blades, and how to shape and sharpen them intelligently instead of just monkeying around. Please be sure to BYOB (bring your own bananas).
Dealing With SkewampusBlades
Skewampus is an interesting word I learned from my mother. I am told it is a combination of the word “Cattywampus” meaning “in disarray,” and “askew.” I think it is the perfect word for describing the ailments some blades suffer.
While less than ideal, it is not unusual for the thickness of a chisel blade’s cross section to vary slightly across its width, with one side being thicker than the other, forming an irregular quadrilateral cross section. This irregularity is found in plane blades too, but it is not typically a problem. Since there is more steel on the thicker side, the cutting edge will tend to develop a skew during sharpening.
Japanese plane and chisel blades are formed by laminating a layer of hard steel to a much softer body made of extremely low-carbon steel or iron. If the lamination exposed at the cutting edge is not uniform, the area of the blade with more hard steel touching the sharpening stone will abrade slower than areas with less exposed hard steel such that the cutting edge will tend to become skewed during sharpening. Perfection is not required, but the uniformity of the lamination is an important detail to observe when purchasing Japanese tools.
Likewise, Western plane and chisel blades that are not uniformly heat-treated, and that exhibit differential hardening across the bevel’s width, will also tend to become skewed during sharpening as one side of the bevel abrades quicker than the other. This problem is more common than you might imagine, especially in the case of inexpensive tools where appearance and low price are given higher priority than quality.
Anyone that has experience bidding high-dollar construction projects will understand the statement “the most profitable job may be the one you lose.” Cheap tools are much the same way: that low-cost chisel or plane may look good on paper, but if you count your time worth anything, if you dislike headaches, and real-world performance matters to your bottom line, then such a tool is often disastrous. Caveat emptor, baby.
A chisel or plane blade that has an irregular cross section or a skewed cutting edge may not be a problem for many cutting operations. However, when cutting mortises, a chisel blade with a skewed cutting edge or irregular cross section will tend to drift to the side gouging the mortise’s walls and ruining tolerances. If you find that your mortise walls are gouged, or that tolerances are poor, check your chisel blade’s shape, and correct any deformities.
Like all human work spaces, Japan’s smithies are not immune from pixie infestation despite annual blessings by Shinto priests and periodic offerings of rice, salt and wine to the spirits. In a previous post we discussed supernatural predators, so I will refer you to it for antidotes to pernicious pixie pox. But the deformities we are examining in this post are more often the natural result of the human eye misjudging hammer blows or non-judicious use of grinder wheels rather than precocious pixies at play.
If your blade’s deformity is not excessive, you can compensate by applying a little extra pressure on the blade’s thicker side while sharpening it.
It is interesting how a little off-center pressure on a blade being sharpened over many strokes can change its shape. Many people unintentionally deform their cutting edges by not paying attention to the amount and location of the pressure their fingers apply. A word to the wise.
Another potential solution is to skew the blade in relation to the direction of travel when sharpening the bevel. This works because the leading corner of a skewed blade is abraded quicker than the trailing corner. But once again, inattention causes many people to skew their blades when moving them around on their sharpening stones unintentionally creating, instead of intentionally correcting, skewed cutting edges. There is nothing wrong with skewing the blade when sharpening so long as you are aware of the distortion this practice can produce and compensate accordingly. Another word to the wise.
If these methods don’t compensate adequately, you may want to grind and lap a chisel blade to a more uniform cross-sectional shape. A chemical bluing solution used afterwards will help conceal the shiny metal exposed by this operation if your chisel objects to the shiny spots. Some of them can be quite vain, you know.
Cutting Edge Profiles
Many people have access to electrical jointers and planers, but relatively few have industrial equipment with the capacity to dimension wide boards such as tabletops. And of course architectural beams and columns are typically too long or too heavy to dimension with most stationary electrical equipment.
The choices available to most people for dimensioning such materials therefore are either handheld electrical power planers and/or sanders, or axes, adzes and hand planes. Powerplaners, sanders, axes and adzes are beyond the scope of this article, but we will look at hand planes.
Although the very idea gives some woodworkers vapors (I don’t mean gas), an efficient craftsman will have multiple planes with cutting edges honed to profiles matched to specific operations.
Everyone that dimensions larger pieces of lumber by hand needs a plane with a wide mouth and a curved or “cambered,” cutting edge called a “scrub plane” in the West, and “arashiko kanna” in Japan.
This variety of plane excels at hogging a lot of wood quickly when the craftsman needs to significantly reduce the thickness of his lumber. If the blade is narrow and curvature is deep, this plane will hog wood quickly, but leave a deeply rippled surface, often with bad tearout.
One might also have a second arashiko, or jack plane with a wider blade with a shallower curvature for the next steps in the dimensioning process. Such a plane will not hog wood as quickly, but it will produce a surface that is closer to flat and smooth and with less tearout. You can see the advantage of having two arashiko planes, or a scrub plane and a jack plane, with different cutting edge profiles when dimensioning lumber.
Many Gentle Readers use electrical-powered planes to dimension lumber before turning it into furniture, doors, chairs, or sawdust, etc. and are aware that planers always leave tiny ripple-like scallop cuts on the wood’s surface, along with some tearout. This will not do as a final surface. A hand-plane finish is far superior, but it doesn’t make sense to remove any more than the bare minimum of wood necessary to remove the washboard.
A finish plane is the perfect tool for this job on condition that it is sharp, set to a fine cut, the chipbreaker is tuned and set properly, the blade profile is appropriate for the width of the wood to be finished, and the wood does not have too many large knots. In one or two passes such a plane can easily remove the ripples and leave the wood clean and shiny without changing its dimensions much at all.
Assuming the wood is cooperative and one knows how to sharpen and setup their plane properly, blade profile frequently remains a key factor many fail to grasp. Obviously, the curved cutting edge of a scrub plane cannot produce the perfectly flat surfaces required for joining two pieces of wood together. On the other hand, the corners of a perfectly straight blade will leave clearly visible steps or unsightly tracks on the surface of a board wider than the blade, which is not a problem when rough dimensioning a board, but is painful to see if the board’s surface is to be left with just a planed finish.
So how do we solve this conundrum? When finish planing, the professional approach is to use two planes each with a different cutting edge profile. The first type of finish plane has a perfectly straight cutting edge used to plane pieces narrower than the blade’s width. Since the blade’s corners are not riding on the wood while cutting it, they won’t leave tracks and ridges.
The second type of finish plane found in the professional’s toolkit has a curved cutting edge, or more correctly, curved just at the corners to prevent it from leaving tracks and ridges when planing boards wider than the blade. Nearly all the edge is left straight, but creating this tiny amount of curvature at the right and left corners causes it to smoothly disappear into the plane’s mouth so no tracks are made and any ridges are nearly impossible to see or feel. In other words, the corners of the cutting edge never touch the surface of the board, and so don’t leave discernible tracks or ridges. The finer the cut made the smaller any ridges created will be. Indeed, where a high-quality surface is required, the final cut with the finish plane will produce shavings thin enough to see one’s fingerprints through.
You may want to reread the previous two paragraphs to make sure you understand what these two cutting edge profiles are and what they can accomplish before you read further.
Naturally, a professional doing high-quality work needs at least two finish planes, one with a straight cutting edge used to produce flat, precisely-dimensioned surfaces on wood narrower than the blade’s width, and another finish plane with a cutting edge very slightly curved at the corners used to finish wider surfaces.
There are those that advocate using a curved blade, sometimes dramatically “cambered” as some call them, for all applications. Those who teach this sloppy technique twist themselves into knots justifying tricks to approximate flat surfaces using such blades. I have no doubt this is an ancient technique, but I think it is a sad practice that sprung from the carelessness of some craftsmen in flattening their sharpening stones, and with time this bad habit became a tradition in some quarters. I strongly suspect fans of this strange way of doing business habitually sand all visible surfaces anyway so tracks and ridges are not a problem for them. But the fact remains that perfectly flat, track/ridge-free surfaces work best for joinery.
Tradition and “monkey see monkey do” are a useful place to start, but as his skill level increases, the thoughtful and efficient craftsman will eventually seek to confirm the validity of the traditions he has been taught. I urge you to get started early.
Sadly, too many people never notice the strange instruction label pasted to their boot’s sole, nor that smelly stuff sloshing around inside.（ツ)
As we come to the end of this post, my advice to you, Gentle Reader, is to learn two bedrock basic skills to perfection. First, learn how to keep your sharpening stones flat; And second, learn how to sharpen your blades to have a straight cutting edge. Everything else will flow naturally from these skills. Your blades deserve it. We will talk more about these subjects in the future.
In this post, we have discussed 12 serious points about plane and chisel blades and how to use and improve them all but a few woodworkers in the West are unaware of, or ignore, but which are common knowledge among professional Japanese woodworkers in advanced trades. While condensed, it is enough information to fill a book, but we are giving it to you for the price of bananas (BYOB, remember?). We hope you picked up on each point, and test those that are new to you.
The next installment in this simian soap opera of sharpening will focus less on monkeyshines, and more on stones and techniques. Please stay tuned.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form located immediately below.
Pixie, kobold, elf, and sprite,All are on their rounds tonight;In the wan moon’s silver ray, Thrives their helter-skelter play.
Gentle Reader, have you ever placed a tool down, only to later discover it has vanished into thin air? Do your tools ever become unexplainably dull or corroded within what seems like just a few days after cleaning and sharpening them? If so, you may have an Iron Pixie infestation without realizing it.
Respected fairyologists theorize that, unlike their timid brethren frolicking in forests, or their blingy cousins in Hollywood, New York, and Washington DC who delight in tricking the mass media, film industry and corrupt politicians into constantly making greedy, immoral, hypocritical fools of themselves, Iron Pixies (genus Fatum Ferrum), do not fear iron or iron alloys. Indeed, besides pilfering and concealing tools that contain iron, they love nothing more than to use their corrosive powers to return this metal to its natural state through the thermodynamic chemical process known as “rubeum, et conversus abibo” (turn red and go away).
These piratical pixies become especially joyful if the owner of the snatched tool is unable to find it after much frantic searching, and is eventually forced to buy a replacement. Only when they see the replacement tool will the pernicious pixies permit the owner to locate the pilfered tool, usually rusty and chipped.
We’ll come back to the supernatural aspects of woodworking tools, but first let’s examine some more mundane details about sharpening blades, and a few things that typically go wrong with them.
The Ideal Bevel Angle
There is such a thing as an “ideal bevel angle” for each blade in each cutting situation, one that cuts the wood quickly, cleanly, with minimum force expenditure and that keeps the blade effectively sharp for the maximum amount of cutting possible, but determining this angle is not an easy calculation since it is difficult and expensive to actually observe what is happening at the cutting edge from a shaving’s-eye-view.
For example, a steep 60° bevel angle on a chisel will support the cutting edge thoroughly and will be durable, but it will pound the wood more than cut it wasting time and energy and damaging the wood unnecessarily. On the other hand, a 15° angle will cut well, but is likely to chip and dull quickly. A balance is necessary.
This balance will depend on many factors including hardness and abrasiveness of the wood you are cutting at any time (e.g. Sugar Pine versus Ipe), the quality and nature of your chisel blade, the type of cut you are making (low-pressure surface paring versus high-pressure deep mortises), and the care you take to protect the cutting edge. Yes, technique matters.
Determining the ideal bevel angle is ultimately a trial and error process the diligent craftsman will unconsciously perform until it is second nature, but the following are some general guidelines to get you started.
Most Japanese woodworking tools, including plane blades and striking chisels (oirenomi, atsunomi, tatakinomi, mukomachinomi) perform well in most construction and furniture woods with the standard 27.5°~30° bevel angle. This is a good compromise, acute enough to cut most wood efficiently without too much friction, while still providing adequate support to the thin cutting edge to avoid chipping.
But like any rule, there are exceptions. For example, 35° is often a superior bevel angle for chisels when quickly cutting mortises in harder woods or planes shaving tropical hardwoods.
When cutting very soft woods, such as Paulownia, similar to balsa wood, a 22~24° bevel angle may work best.
Paring chisels (tsukinomi), when used properly, are subject to less violent forces than striking chisels, and can handle a 24° bevel angle. But for most woods, a professional-grade Japanese plane or chisel blade will likely experience chipping if the angle is much less.
There are many variables and potential solutions one might consider, but as a general rule, I recommend starting your experiment with a 27.5~30° bevel angle for plane and chisel blades.
If you find that your blade chips or dulls quicker than you think it should, increase the angle gradually until it calms down. This can result in a double-bevel blade, one difficult to sharpen freehand. In this case, I fully support using a honing jig, at least until you achieve a flat bevel wide enough and stable enough to sharpen freehand. But don’t handicap yourself by relying solely on honing jigs because they can become like training wheels on a bicycle: slow and childish.
Mercurial Bevel Migration
There is a strange, almost supernatural phenomenon many woodworkers experience, the first evidence of which is a plane or chisel blade that previously held a sharp edge a long time suddenly and unexplainably beginning to dull or roll or chip sooner than before. Even professionals with many years of experience occasionally see their tools exhibit this nasty behavior.
Some craftsmen faced with this dilemma begin to question their sanity. They may ask themselves: “Has heaven turned its face against me? How do I rid myself of this curse? Do I need to see a shrink?” Other craftsmen, more aware of the dangers of pernicious pixies, draw strange hex symbols on their walls or inlay brass circles and pentagrams into their floors to exorcise them from their workshop. Indeed, this practice has a long history in Europe and America.
Unfortunately, more than one blacksmith has been falsely accused of poor workmanship when the fault actually lay with the tool’s owner unwittingly allowing Iron Pixies to run amok. If this happens to your tools, please use the methods described below to purge any pestilent pixies in the area.
You would be wise to consider all possible causes of Mercurial Bevel Migration (MBM), including those unrelated to any infernal fiends that may or may not be skulking in your lumber stacks.
But if not pesky pixies, what else could cause this maniacal metallurgical malfeasance? Never fear, Gentle Reader, there is another possible explanation, one that can be resolved without paying for years of expensive psychotherapy and mind-altering drugs, or placing small bowls of blood and milk around your workshop, or enduring the pain of tattoo needles, or paying for stinky ceremonies involving burning sage and spirit drums.
The more likely cause is simply that it’s human nature when sharpening chisels and Japanese blades with their laminated, top-heavy construction to apply more pressure to the bevel’s rearward half (farthest from the cutting edge) abrading the softer jigane body more than the harder hagane cutting layer. Eventually, as the soft jigane wears away, the bevel angle will decrease to the point where the cutting edge will lose support and become fragile.
Once you are aware of this tendency and take preventative measures (and assuming you don’t have an iron pixie infestation), all should be well.
Next let’s examine some measures to get rid of both this bad habit and trixy pixies.
Pixie Predation Prevention & Pacification
If you suspect the presence of iron pixies, you should perform a Pixie Detection test. A reliable method is described in the next section below.
In any case, to avoid pixie infestation, you should create a workshop environment unfriendly to pixies. The following is an partial list of measures I have found to be effective.
Cleanliness: Clean bench surfaces and sweep the floors daily. Periodically vacuum and wet-mop workshop floors twice a year during the winter and summer solstices (approximately June 21 and December 21);
Add more lighting: Iron Pixies fear light because it reveals them to their enemies;
Keep a pair of boots near the door into the workshop: Pixies are deathly afraid of boots, especially when they contain the feet of sharp-eyed human children, but just the sight of boots will prevent them from entering a space;
Keep brass benchdogs in your workshop. Expert fairyologists insist, and I agree, that having a brass bench dog (remember, Iron Pixies do not fear iron or steel or the IRS) or two close by will banish Iron Pixies to the workshop’s dark recesses and keep their nasty claws away from tools. The deterrent effect of bench cats is unclear, but if you decide to rely on one, be sure it bothers to stay awake;
Welcome spiders: Although this may seem to contradict No. 1 above, Iron Pixies fear spiders, especially daddy longlegs, who tangle them in their webs.
Make regular offerings to the gods of handsaws. More on this subject in future posts.
A more mundane but sure way to prevent MBM is to make or buy a bevel angle gauge and regularly use it to check your bevels during sharpening. Aluminum, stainless steel or even plastic gauges will work of course, but brass or bronze are more effectual at purging perfidious predatory pixies because copper is toxic and zinc causes pixies indigestion. Be sure to store it close to your valuable steel tools to help repel the maniacal monsters.
Here’s the important thing: once you have this tool on hand, use it to check each blade before, during and after sharpening to ensure you are maintaining the correct bevel angle instead of allowing it to decrease incrementally over repeated sharpening sessions. Make this a firm habit. More on this important subject in future posts.
Remember to measure the bevel angle at the blade’s far right or left edges because the hollow-ground ura of Japanese blades makes it difficult to correctly measure the angle if you check it elsewhere.
Pixie Detection Methods
Iron Pixies are secretive creatures most people never see, but if you suspect you have an infestation, a detection test is called for.
While there are many proven methods to test for pixie infestation, the least expensive non-toxic iron pixie detection test is to sharpen a plane blade, and while doing so, attempt to “stick it” on the stone as in the photo below. This phenomenon is evidence the stone and the blade are in such perfect contact that the suction between the blade, water and mud on the stone’s surface strong is enough to support the weight of the blade.
If you are unable to accomplish this marvelous feat even after many attempts, you can be assured of the presence of peevish pixies nearby. In that case, use the preventative measures listed in the section above. You should also flatten your sharpening stones (especially the rough and medium grit stones) and make sure your blade’s bevel is perfectly flat. Bulging bevels are the pernicious pixie’s playground. (Aha! Iambic pentameter!)
Fair warning: If you stubbornly persist in your efforts to stick a plane blade before purging the area of pixies, they may go berserk to prevent this sublime event from occurring. If that happens, Katy bar the door!
In the next stage of our adventure, we will examine some of the health ailments blades commonly suffer. High cholesterol in chisels? Planes with pneumonia? Or just toolish hypochondria? Stay tuned to find out more.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form located directly below.
If a craftsman wants to do good work, he must first sharpen his tools.
Confucius, The Analects
We talked about the Ura previously in post No. 9. It is a defining detail in most Japanese woodworking blades, and one we must understand if we are to efficiently sharpen them. In his post we will look into this important feature in more detail.
What is the Ura?
Japanese plane and chisel blades have a unique and intelligent design feature at what is called the “flat” on Western plane and chisel blades, called the “Ura” (pronounced oo-rah).
Ura translates into the English language as “bay,” as in a protected area where the sea meets the shore. At the center of the ura is a hollow-ground, depressed area in the hard steel hagane layer that serves two purposes.
One purpose is to make it easier to keep the blade’s “flat” (the shiny areas surrounding the depression) planar (in the same plane).
If you pay attention when sharpening your wide Western chisels and planes you will notice that, after many sharpening sessions, the blade’s flat, which was once planar, becomes convex with a high point at the flat’s center making it difficult to keep the extreme cutting edge, especially the corners of the blade, in close contact with the sharpening stone. Yikes!
This doesn’t occur because you don’t know how to sharpen your blades, but simply because your sharpening stones/platens/paper tend to abrade the blade’s perimeter more aggressively than the center. The resulting curvature makes it more difficult to polish the flat’s extreme cutting edge. Major buzzkill.
Because of the Ura, Japanese woodworking blades are quickly fettled initially and tend to stay planar without a second thought for many years of hard use, an important benefit if you count your time worth anything.
Another purpose of the Ura is to reduce the square inches or square millimeters of hard steel you must polish during each sharpening session. As you can see from the photo above, the shiny perimeter land is all that touches the sharpening stone. Compare this with the black area which doesn’t touch the stone. That’s a lot of hard steel you don’t have to deal with. Besides making the job easier, it also saves a lot of time when sharpening and helps one’s expensive sharpening stones last longer. Time is money and stones ain’t cheap, as my old foreman used to say. Even if you don’t use your tools to make a living, remember that time spent sharpening is time stolen from the pleasure of making wooden objects.
The Downside Of the Ura
The Ura detail is not all meadow flowers and fairy farts, however, because it does have one unavoidable downside: Over many sharpening sessions the Ura unavoidably becomes gradually shallower, and the lands surrounding the Ura on four sides become correspondingly wider. It is not uncommon to see old chisels and plane blades with the depressed area of the Ura almost gone. You can postpone this day by sharpening the Ura wisely. However, in the worst case where the Ura disappears entirely, you will still be left with an entirely usable Western-style flat, so not all is lost.
In the case of plane blades, unless the plane’s ura is subjected to a brutal sharpening regime, the land that forms the cutting edge (called the “Ito ura” meaning “strand” as in a flat area on a riverside, in Japanese) tends to gradually become narrower, and even disappear entirely after numerous sharpenings. Of course, when this happens, the blade loses its cutting edge, and the land must be restored by “tapping out” or bending the cutting edge towards the ura side, and then grinding it flat to form a new ito-ura land. Tapping out a blade requires some caution, but is not difficult. I will not deal with this aspect of blade maintenance in this post.
In the case of chisels, which have smaller and shallower ura compared to wider plane blades, the land at the cutting edge does not typically require tapping out, although it’s certainly possible to tap out wider chisel blades. Narrow chisel blades, on the other hand, are difficult to tap out without damaging them due to the rigidity produced by the hard steel layer (detailed in the previous post in this series) wrapped up the blade’s sides.
Some chisels are made with multiple ura, typically called “mitsuura” meaning “triple ura.” Mitsuura chisels are more difficult to sharpen because the area of hardened steel that must be polished is larger. The Ura of mitsuura chisels also tend to wear-out quicker than single-ura chisels because each individual ura is shallower in depth than standard Ura. I am not a fan of multiple ura except in a few specific applications.
In the next stage of our journey into the mysteries of sharpening, we will wander through the metaphysical realms of the “Fae.” Be sure to have a brass bench dog in your pocket when we leave the well-lighted pathways.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form located immediately below.
Our customers outside of Japan frequently need some information to help them select the best wood for their chisel handles. In this post I’ll describe the woods available and the advantages and disadvantages of each to help you make an informed decision.
The chisels we sell all have wooden handles in several varieties of wood, the two most common being Japanese White Oak and Japanese Red Oak. We also can provide handles for some chisels in Gumi (Silverberry wood), Ebony, and Rosewood. Let’s look at White Oak first.
Japanese White Oak
Japanese White Oak (JWO) is very similar to American White Oak in that it is closed grain, dense, and has medullary rays. The color is a little whiter than the American or European varieties, and in fact, it’s a little denser and stronger than either. It holds up well to being struck with steel hammers.
JWO is not a slick wood when dry and does not become slippery when wet, important characteristics in a tool handle where staying attached to the blade and staying secure in a sweaty hand while being pounded on are part of the job.
Like White Oak everywhere, it contains tannic acid. In fact, bark and chips from this wood have been used since before written history to tan leather because this chemical converts animal skins that would otherwise rot into durable leather. Tannin, which is the base word of both tanning and tannic acid, comes from the medieval Latin word tannāre, a derivative of tannum (oak bark), from which the tannic acid compound is derived.
Tannic acid can react with some people’s sweat causing the wood to turn a dirty grey color. This tendency is not strong among the Japanese people, but it is among many caucasians, including me.
This discoloration in no way weakens or harms the wood, it just makes it look dirty.
JWO generally has a bland, indistinct grain with few flecks, not a problem for a tool handle or plane block, but less than ideal for furniture.
Japanese Red Oak
Japanese Red Oak (JRO) is as different from American Red Oak as the “the moon and a mud turtle,” as they say over here. It is a much more useful wood.
Similar to JWO, Japanese Red Oak is closed grain and also has medullary rays. It contains much less tannic acid, and ranges in color from a dark red (difficult to obtain nowadays) to a pinkish red.
JRO has been prized in Japan for tool and weapon handles since forever. Indeed, JRO is the preferred wood for the bokken wooden swords used in the martial arts. The better grades are denser than White Oak with a more interesting grain. Unfortunately, this grade of Red Oak has become difficult to obtain.
As with Japanese White Oak, Red Oak is not a slick wood when dry and does not become slippery when wet.
There are unscrupulous people that dye less colorful pieces of Red Oak a dark red color to jack up the price. We don’t deal with such slimy people and our JRO handles are all authentic. Caveat emptor, baby.
JRO has the advantage of discoloring less than JWO over time and tends to look cleaner longer. It makes a more attractive handle.
The downside to the JRO generally available nowadays is that it is a little less dense than White Oak. I consider Japanese Red Oak to be the perfect wood for paring chisels, and Japanese White Oak the perfect wood for atsunomi chisels. Either wood works fine for the smaller oiirenomi bench chisels.
Gumi (Elaeagnus multiflora or cherry silverberry) is more a hedgewood or bush than tree. It has historically been cultivated primarily for the fruit it bears. It is stronger than Japanese White Oak, but lighter in weight. It has a distinctive yellow color that some people find attractive. I don’t get the attraction, but must admit it has a striking appearance.
Gumi makes a fine, durable handle. It is a more expensive material. My handlemaker has shorter pieces suitable for oiirenomi handles in-stock, but nothing longer.
Gumi handles are custom order.
Ebony and Rosewood
Ebony and Rosewood make elegant, durable, well-balanced handles for paring chisels, which are never struck with hammers and therefore unlikely to crack. But material costs are quite high. They are also custom order items that take some time to fabricate.
Oirenomi and atsunomi and other types of tatakinomi with ebony or rosewood handles look great. And in the case of amateurs that buy such chisels (from other sources) just to collect and/or admire, I have nothing to say. But we sell professional-grade tools to be used on real-world jobsites and in workshops by serious craftsmen for serious cutting, not to become safe queens. Using ebony and rosewood handled oirenomi or other varieties of tatakinomi to do real work is like wearing Jimmy Choo stilletto heels to a construction site.
Yes, Jimbo makes elegant shoes. And if your ensemble is well thought-out, a pair of his heels will make your legs look mahvelous dahling, simply mahvelous. Sadly, they will neither last long nor get the job done. Other workers will mock you behind your back. And embarrassing stuff will happen at the worst possible time.
For warranty reasons, we do not sell tatakinomi of any kind with handles of ebony or rosewood. They are too easily and irreparably cracked/damaged if struck with a steel hammer. Professionals will not purchase, and we will not sell, such silly tools.
While it has not been a problem so far, importation of some exotic hardwoods such as Brazilian rosewood into the United States can be a problem, according to the guitar makers I know and information on the infallible internet (ツ). If you order handles made from these woods, please be aware that you become the responsible importer once such materials cross into the jurisdiction of your local Customs Office. They may confiscate your tools or levy fines. The risk is all yours. That said, it has not been a problem so far.
Not encouraging, I know, but customs services worldwide are in the business of making literally tons of money every hour by taxing the entire world using their absolute authority within their bailiwick, and lots of guns. The most profitable income source for governments, as you know, is not taxes but making and circulating money (literally manufacturing money), followed by customs fees. Such it has always been; such it will always be.
On the other hand, we have experienced difficulties and customs duties in only two countries, namely Spain, which is notorious for once charging confiscatory import duties on gunpowder and cannonballs brought into Spain by Great Britain to free that country from Napolean’s armies during the French occupation.
Australia was brutally difficult on one occasion, but that incident may have been driven more by dazzling government incompetence rather than enforcement of the country’s importation laws.
For standard oirenomi and other tatakinomi intended to be struck with a steel hammer, either White Oak or Red Oak are entirely adequate and cost-effective. White Oak is a little stronger, but its appearance does not improve with use or age. Red Oak is not quite as dense and strong, but it is sufficient for these chisels and looks better over time.
For wider Atsunomi and Mukomachinomi (mortise chisels) which will see heavy use, White Oak is the best choice due to its higher density and superior strength.
If cost and delivery time is not a concern, you like the yellow color and want to be different, then gumi is an excellent choice for oiirenomi. It’s the same as the difference between brown leather work boots and tan-colored Timberland boots.
For usunomi and other paring chisels not intended to be struck with a steel hammer, Red Oak is the best choice, IMO, but White Oak will perform just as well. Gumi is not an option. Ebony and Rosewood look beautiful and feel nice (if you don’t have allergies to Rosewood), but are expensive and require lead time.
“It is our choices, Harry, that show what we truly are, far more than our abilities.”
J.K. Rowling, Harry Potter and the Chamber of Secrets
If you are reading this, it’s safe to assume you are interested in sharpening woodworking blades. You may have little experience with Japanese tools, and even then you may not be aware of some of their important details. In this post we will try to remedy that by examining some simple historical points common to woodworking blades around the world, as well as some details that make Japanese blades unique.
I believe an understanding of these basic facts will you aid your sharpening efforts, or will at least tickle your interest in Japanese blades. Please comment and let me know your thoughts.
Laminated Bi-Metal Construction
As discussed in previous posts in this series, before technological advances in the 1800’s steel was difficult to make and expensive. Consequently, it was standard practice not only in Japan, but everywhere including Europe and the United States, to reduce costs by minimizing the amount of precious steel used to make axe, scythe, plane and chisel etc. blades by laminating smallish pieces of high-carbon steel to softer and much cheaper wrought-iron bodies through a process called “forge welding.”
Most chisel and plane blade blacksmiths in Japan continue to employ this lamination technique even today, not out of some navel-gazing preference for the archaic, but because it has serious advantages.
The best Japanese plane and chisel blades are generally comprised of a layer of very hard high-carbon steel called “hagane” (鋼) in Japanese, forge-welded to a softer low-carbon (ideally no-carbon) iron body called “jigane” (地金). We discussed both of these metals in the previous two posts in the series. Hereand here.
Why go to so much trouble? One advantage of this construction is that it allows the cutting edge to be made much harder, and therefore cut effectively longer than a blade of uniform hardness. For instance, a blade made entirely of steel hardened to HRC65 might cut very well, but it would break or shatter in use. And even if it did not break, it would be time consuming and irritating to sharpen such a wide expanse of hard steel. Remember, the harder a piece of steel is the more work it takes to abrade it.
By combining a thin layer of this very hard steel with a thicker layer of soft low-carbon steel or wrought iron the blade can be made thick, rigid, resistant to breaking, and will hold a sharp edge relatively longer while still being easy to sharpen. This once-common ancient structure is clearly superior to all other structural systems for planes and chisels at least.
Laminated Blades in the West
If you have examined antique plane blades with wooden bodies you may have noticed many have blades stamped ” Warranted Cast Steel”
Despite being designated “cast steel” in England and America in past centuries, unlike Conan’s Daddy’s sword, or the orc blades made by in Isengard, plane, chisel and saw blades with this mark were not “cast” by pouring molten metal into a mold to form a blade. Rather the process to make the steel involved melting steel in a crucible and pouring it into molds “casting” a piece of high-carbon steel which is then forged to make the blade, hence the name.
This technology was widely used in the United States and Europe through the 1860’s. In fact, one steel mill is said to have been producing crucible steel until the 1960’s. Toolmanbloghas an interesting summary on cast steel.
With few exceptions, these plane blades have a thin piece of high-carbon steel forge-welded to a soft wrought iron body, very similar to Japanese plane blades. I have used a couple of these antique blades to make Krenovian planes and testify of their excellent cutting ability.
Chisels were also once made in Europe using this same lamination technique, although fewer examples remain extant.
Axes, hatchets, and many farming implements were also mass-produced up until the 1920’s in the US using a variation of this same technique with a “bit” of steel forming the cutting edge laminated to or sandwiched inside a body of low-carbon steel or wrought iron. Axes are still made this way in Japan. It’s a proven technique with a lot of advantages, but it does require a skilled blacksmith to pull off successfully.
The point I am trying to make is that blades made using forge-welded laminated technology were the very best available in Europe and the United States for many centuries. It is sad that this superior technology has been discarded and forgotten except in Japan, but wars and economics change everything while people remain the same.
The shape of the hard steel cutting layer laminated to the softer low-carbon steel (or wrought iron) body was historically a simple flat plate in Western blades. This is also the case for Japanese plane blades, axes, and farming implements. But if you imagine Japanese blacksmiths would be satisfied with such a simple design for all applications, you don’t know the Japanese mind well.
Notice the lighter-colored hard steel lamination wrapped up the chisel’s sides in the four photographs above forming a “U channel” of hardened steel adding necessary rigidity and strength. This is a critical detail for Japanese chisels intended to be struck with a hammer. Interestingly, carving chisels are not typically made this way.
Plane blades are not subjected to the high loads chisels experience and so would not benefit from this structural detail.
Japanese chisel and plane blades, among others, typically have a hollow-ground depression called the “Ura” (pronounced “ooh-rah”) which translates to “ocean” or “bay,” located at what is called the “flat” on Western blades. Notice the polished hard steel lamination extending from the cutting edge to several millimeters up the neck. The black area surrounded by the shiny lands is the same hard metal, but has been ground to form a hollow called the “ura.”
This clever and effective design detail is unique to Japanese tools to the best of my knowledge. We will look at this design detail more in the next post in this series.
What does any of this have to do with sharpening? Glad you asked. This design has some potential disadvantages that have been cleverly turned into distinct advantages you need to understand when sharpening Japanese woodworking blades.
For instance, the layer of high-carbon steel laminated into our chisels and planes is usually 64~65 HRc in hardness. The typical Western blade is made much softer at 50~55 HRc to avoid breakage. This extra hardness makes the blade stay sharper longer, an important benefit if your time is worth anything. This is good.
But if the entire blade were made of a solid piece of this extra-hard steel, it would a royal pain in the tukus to sharpen, I guarantee you. It would also break. That would be bad.
The softer low-carbon/no-carbon steel or iron body, however, is much softer and easily abraded making it possible to keep the hard steel layer thin, and therefore easily abraded, while protecting it from breaking. This is good.
Unlike the blade’s bevel, however, the ura is all one-piece of hard steel. Without the ura depression, you would need to abrade all that hard steel to initially flatten and regularly sharpen the blade, a necessity I guarantee would ruin your mellow mood without massive quantities of controlled substances. But with the addition of the ura detail, we only need to abrade the perimeter planar lands (the shiny areas in the photos above) around the ura. This is exceedingly good.
The ura depression makes it easier and quicker to not only sharpen the blade, but also to to keep the “flat” planar (in a single plane). Without the ura, such a hard blade would be difficult to maintain planar and frustrating to sharpen. With the addition of the ura, the blade is genius.
An important skill to learn when sharpening Japanese blades is how to maintain the lamination and ura effectively. We will discuss this important subject more in future posts.
If you didn’t learn at least three new things from this post then you are either very smart or weren’t paying attention. ¯\_(ツ)_/¯
In the next installment in this bodice-ripping tale of romance and derring-do we will examine the hollow-ground “Ura” in more detail. It’s important enough to deserve a special post.
Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the question form located immediately below.
If you can’t explain it to a six year old, you don’t understand it yourself.
In the previous post on sharpening Japanese woodworking tool blades we looked primarily at the nature of the hard high-carbon steel used in making woodworking blades. In this post I will try to dispel some of the confusion that surrounds the other metal used in making most Japanese knives, axes and woodworking blades, namely the soft low-carbon steel called “Jigane” (地金). I hope this brief explanation will improve your understanding of some Japanese tools and aid your sharpening efforts.
Sources of Jigane
Most Japanese knives and woodworking blades are comprised of a thin piece of hard high-carbon steel, discussed in my previous post, forge-weld laminated to a piece of softer low-carbon steel or wrought iron called “Jigane” (地金) in Japanese, which translates directly to “ground metal.”
I will write more about this bi-metal lamination in the next post in this series, but for now take my word that it is essential to the performance of many types of Japanese cutting tools nowadays, and for many centuries was critical to manufacturing cutting tools in America and Europe as well.
The best jigane material for plane blade bodies is said to be scrap iron from the boilers of old trains, boats, and factories, etc.. Such boiler tanks were subjected to thousands of heating and cooling cycles during their years in service which drove out impurities, including carbon, making the iron very soft to the point of weakness.
The most desirable jigane for plane blades is called “tired” iron, named because it is not only soft, but looks weak and exhibits a visible grain along with cracks and imperfections which those familiar with Japanese plane blades covet.
Wrought Iron Production
Nowadays, this very low-carbon steel, also known as “ wrought iron” is not produced in any volume for several reasons. First, demand is just too low to make it worthwhile to manufacture. Hand-forged ornamental iron is the only commercial usage besides Japanese tools, truly microscopic markets.
The second reason is that steel manufacturing processes have changed drastically in the last 100 years. For instance, it used to be that steel began as iron ore, basically rocks and dirt, which was melted and refined into low-carbon wrought iron, so wrought iron was an intermediate product of steel production. Indeed, this low-carbon product was much less expensive to produce than high-carbon steel and so was used for everything from the boilers, bridges, trains, ships and anchor chains mentioned above to axes, chisels, farming implements, machinery, what’s called “miscellaneous metals” in the construction industry, and of course plane blades. There are still a few surviving structures that were made using this archaic material.
Nowadays, things are very different. Carbon is incorporated into the steel early in the manufacturing process, so low-carbon wrought iron never becomes an intermediate product.
Also, scrap metal has become critical to steel manufacturing processes nowadays. Remember what happened to steel prices worldwide when China was buying up huge volumes of scrap metal worldwide for its Olympic infrastructure building projects?
I think we can agree that this energy-efficient cost-reducing recycling of natural materials, one that was hardly an option 150 years ago, is a very good thing. But it does have a tiny downside, namely that most commercially-available scrap metal available in any useful volume today has been through the modern steel-manufacturing process many times and already contains not only high levels of carbon, relatively speaking, but alloys such as chrome, molybdenum, and nickel from previous melting pots. Indeed, undesirable chemicals such as phosphorus, sulfur and silica tend to be high in general junkyard scrap metal. On the other hand, keeping these unintended alloys and impurities under control is a serious challenge for manufacturers of tool steel.
In summary, wrought iron simply isn’t made anymore, and it is not a sustainable, profitable product.
Japanese blacksmiths making high-quality plane blades nowadays mostly use wrought iron recycled from old anchor chains, old iron bridges, or other recycled iron structural components. If you see a hole in a plane blade, like the extra-wide plane blade pictured at the top, it once housed a rivet. Yes, structural steel was once connected with hot rivets instead of bolts. Hi-tensile modern bolts are better.
Mr. Takeo Nakano (see his photo below) makes my plane blades. He is a kind, quite man with the outward appearance of a sedentary grandfather, but when using hammer and tongs at his forge within his dark smithy, his posture and visage reminds me of an intense Vulcan reinforcing the gates of Hades.
Like nearly all the plane blacksmiths in Niigata, he uses scrap iron obtained in a single lot many years ago from an iron bridge that was dismantled in Yokohama Japan.
I am told that most of the jigane used for plane blades in Hyogo Prefecture is old recycled anchor chains.
In the case of plane blades, structural strength is not critical, so laminating a thin layer of high-carbon steel to form the cutting edge to a soft iron body is adequate. Indeed, the thicker the hard steel layer, the more time and effort it takes to sharpen the blade, so in a high-quality blade the thicknesses of the high-carbon steel layer and the soft jigane body will be carefully balanced to ensure the blade’s bevel rides the sharpening stones nicely and can be quickly abraded.
Plane blade blacksmiths use the same strip jigane used for chisels for making less-expensive plane blades.
In the case of chisels, while ease of sharpening is still important, the body and neck must be harder/stiffer to prevent them from bending, so a different, stiffer variety of jigane with a higher carbon content and fewer defects is used, and the steel layer is typically made thicker.
The jigane used by my chisel blacksmiths is a commercial product not produced anymore (thank goodness they have stockpiles) called “gokunantetsu” 極軟鉄 which translates directly to “extremely soft iron.” With a carbon content of 0.04~0.07%, a better description would be “very low carbon steel.” When heated and quenched, it doesn’t harden much.
The adventure will continue in the next exciting episode where we will bring it all together into a blade. Don’t forget to have popcorn and jujubes ready.
Behold, I have created the smith that bloweth the coals in the fire, and that bringeth forth an instrument for his work.
Isaiah 54:16 KJV
The blades we are considering in this post are made from iron and steel, so it makes sense to examine these materials from the viewpoints of sharpness and sharpening. In the previous post we looked at some of the supernatural aspects of making and forging steel. In this post we will examine some alchemical aspects.
This post could be very technical, but I have simplified the description of chemical processes to make it easier for the non-technical Gentle Reader to follow. Please bear with me.
The Alchemy of Mutating Iron to Steel
At the heart of steel alchemy is the hardening process. When carbon is combined with iron in the right proportion, steel is formed. This mutation is easily accomplished nowadays, but for most of human history it was a fiendishly difficult, expensive process. No wonder those who could accomplish the deed were attributed with magical powers.
If steel is heated to within a specific range of temperatures (difficult to measure by eye) and then suddenly cooled, crystalline structures containing small, very hard and relatively brittle crystals called carbides form within a softer matrix of iron. These hard carbides are what do the serious job of cutting, not the softer matrix. At the extreme cutting edge, this structure might be compared to a modern circular saw blade comprised of a relatively soft body to which is attached very hard tungsten carbide cutting tips.
A steel blade dulls when these carbide crystals either shatter, or the pressure and friction of cutting wears away or cracks the softer supporting matrix, allowing the carbides to be torn from the matrix leaving behind gaps of soft, blunt metal. The larger the carbide clumps are and the further the distance between them, the more easily they are shattered and torn away, and the duller a blade becomes with each crystal’s failure.
In a low-quality blade, and given the same number of carbide crystals in a fixed volume of steel, the crystals will form into relatively large and isolated clumps separated by wide rivers and lakes of softer metal, as seen from the viewpoint of a carbide. The steel will crack along these weaker pathways when stressed, and when cutting, the softer material in these lakes and rivers will erode first, leaving the carbide clumps unsupported and vulnerable to failure.
In a high-quality steel blade, by comparison, and given the same number of carbide crystals in a fixed volume of steel, the crystalline clumps are comparatively smaller and distributed more evenly throughout the matrix making it more resistant to erosion, and the carbide crystals more resistant to damage. Such steel is called “fine grained,” and has been highly prized since ancient times for its relative toughness and ability to become very sharp and stay sharp for a long time. This is the steel preferred by woodworking professionals in Japan and is the only kind found in our tools. Without exception.
Impurities and Alloys
All iron ores naturally contain harmful impurities such as phosphorus, sulfur, silicon, and manganese to one degree or another. When these impurities exceed acceptable limits, they can weaken the steel, make it brittle, or make heat treatment results inconsistent. They are often expensive to remove.
There are three approaches commonly used to minimize the negative effects of these difficult-to-remove impurities. The first is simple avoidance of the problem by employing iron ore and scrap metal free of excess amounts of these contaminants. Such ore and scrap are available, but they are not found everywhere and are relatively expensive. For centuries, the purest iron ore has been mined in Sweden.
The second approach is to add purer iron or carefully sorted and tested scrap steel to the pot thereby reducing the percentages of the harmful contaminants. This is called “ solution by dilution.”
The third and more common fix is to add chemicals such as chrome, molybdenum, nickel, tungsten, vanadium and even lead to the pot forming steel “alloys.” In their simplest formulations, these chemicals help overcome the detrimental effects of natural impurities, specifically those related to brittleness and unpredictable heat treatment results. Some formulations make the steel less likely to warp and crack despite impurities. Others make the steel more resistant to abrasion and corrosion, or even easier to cast, drop-forge, or machine.
Steel alloys have serious advantages over plain high-carbon steel in mass-production, reducing material costs by improving the performance of cheaper lower-grade iron ore and scrap metal, improving manufacture characteristics, and achieving higher productivity with fewer rejects even when worked by low-skill workers.
But these alloys are not all fuzzy blue bunnies and fairy farts because edged tools made from high-alloy steels typically have some disadvantages too: Due to their crystalline structure, they simply cannot be made as sharp as plain high-carbon steel, and are more difficult and time-consuming to sharpen by hand.
Of course, additives like chrome, nickel, moly and especially tungsten are costly.
Some manufacturers cite the higher costs of high-alloy steels to justify higher prices for their products. However, what they never say out-loud is that labor costs are much much less when using high-alloy steel because skilled workers are not necessary. And because high-alloy steels produce fewer rejects, quality control is easier, overall productivity is higher, warranty problems are fewer, and profitability is increased. Indeed, without high-alloy steels, factories would need to train and hire actual skilled workers and professionals instead of uneducated seasonal workers destroying the world’s current mass-production model. Egads! Walmart’s shelves would be bare!
My blacksmiths make only professional-grade tools for craftsmen that value ease of sharpening and cutting performance above corporate profits. They charge more for plain high-carbon steel blades than for high-alloy steel products because labor and reject costs are higher. So if a manufacturer brags about the excellence of the high-alloy steels they are using rest assured increased profits are their motivation, not improved cutting performance. Caveat emptor baby.
The best plane and chisel blades are made from plain, high-purity, high-carbon steel. In Japan, the very best such steel is made by Hitachi Metals mostly using Swedish pig iron and carefully tested industrial scrap (vs used used rebar and car bumpers), and is designated Shirogami (White-label) No. 1. They also make a steel designated Shirogami No.2 containing less carbon. Another excellent steel for plane and chisel blades is designated Aogami (Blue-label) No.1 and No. 2.
Aogami, like Shirogami, is made from extremely pure iron, but a bit of chrome and molybdenum are added to make Aogami steel easier to heat treat with less warping. Aogami can be made very sharp, but it is not quite as easy or pleasant to sharpen as Shirogami. Some of the plain high-carbon Swedish steels are also excellent.
If worked expertly, either of these steels consistently produce the highest quality “fine-grained” steel blades.
Let’s compare the sharpening characteristics of these two steels. To begin with Shirogami steel is easy, indeed pleasant, to sharpen. It rides stones nicely and abrades quickly in a controlled manner.
Aogami steel, by comparison, is neither difficult nor unpleasant to sharpen, but it is different from Shirogami steel in subtle ways. It takes a few more strokes to sharpen, and feels “stickier” on the stones, but it will still produce fine-grain steel blades and performs perfectly.
Inexperienced people lacking advanced sharpening skills typically can’t tell the difference between blades made from Shirogami, Aogami or Swedish steel and steels of lesser quality. But due to the difficulty of forging and heat treating Shirogami or other plain high-carbon steels, a blacksmith that routinely uses them will simply be more skilled and have better QC procedures than those whose skills limit them to using only less-sensitive high-alloy steels.
Professional Japanese woodworkers insist on chisel blades made from Shirogami steel. Some prefer Aogami for plane blades believing the edge holds up a bit better. My plane blacksmith and carving chisel blacksmith prefer to use Aogami because it is easier to work and more productive (especially in the case of carving chisels), but for a little extra they are happy to forge blades from Shirogami or Swedish Steel.
I own and use Japanese planes made from Shirogami, Aogami, Aogami Super, Swedish steel, and a steel called “Inukubi” meaning “dog neck” which was imported to Japan from England (Andrews Steel) in the late 1800’s. Of these, Shirogami No.1 steel is my favorite. It’s a matter of personal taste.
Beware of a plane blacksmith that refuses to use plain high-carbon steel and tries to charge you more for Aogami or Aogami Super steel.
The Challenges of Working Plain High-Carbon Steel
What makes plain high-carbon steel so difficult to work, you ask? I’ve never even forged a check much less a tool blade, but I will share with you what my the blacksmiths I use and swordsmiths I know have told me in response to this question.
First, plain high-carbon steel is much more difficult to successfully heat treat because the range of allowable temperatures for forging and heat-treating is narrow. Heat it too hot and it will “burn” and be ruined. Quench it at too high or too low a temperature and it will not achieve the desired hardness. Miss the appropriate range of temperatures and the blade may even crack, ruining it. Yikes.
Second, even if the temperatures are right, plain high-carbon steel has a nasty habit of warping and cracking during heat treatment resulting in more rejects than steels with additives such as chrome and moly. Strange as it may seem, when the crystalline structures that make steel useful form during quenching, they increase in volume. This change in volume produces differential expansion causing the metal to warp. This warpage can be more or less controlled, or at least compensated for, by a skillful blacksmith, but it takes real skill, extra work, and a bit of luck. Not just any old Barney can do it consistently, so when working plain high-carbon steel, a blacksmith needs to know his stuff and pay close attention.
Other than wastage due to rejects, it doesn’t cost more to forge and heat-treat a blade of plain high-carbon steel. But it takes serious skills and dedication to quality control to make a living working it for 5+ decades.
Let me give you an example of skill and experience as it relates to warpage management of plain high-carbon steel.
rThe photo below is of a swordsmith just before he quenches a yellow-hot sword blade made of tamahagane, a traditional type of plain high-carbon steel made from iron sand, in a water trough. Notice how his smithy is: he is working in the middle of the night, the time when the best magicians and alchemists have always done the most difficult jobs because temperatures are easier to judge without unpredictable sunlight confusing things. His posture and facial expression are tense because he is about to roll the bones and either succeed in the most risky part of making a sword, or fail wasting weeks or months of work and thousands of dollars worth of materials. Notice how straight the glowing blade is.
Note that the formation of crystalline carbides in Japanese swords after heat treatment is densest nearest the hard cutting edge. The swordsmith therefore forges the blade straight before quenching it in expectation of it warping to the intended curvature when the crystalline structures at the cutting edge form, as seen in the photo below. This curvature is an intentional design feature that takes years of experience to achieve in a controlled manner.
If the swordsmith intended to make a straight sword blade, he would have a forged a reverse curvature into the blade to compensate for the warpage that occurs during quenching. Plane and chisel blades exhibit similar but less dramatic behavior.
The thinner the piece of steel being heat-treated, the more unpredictable the warpage and more likely the blade will develop fatal cracks. Within limits simple warpage can be corrected in thin blades, but not in stiffer chisels or plane blades. In the first few seconds after quenching and/or tempering a blade, the metal is still a bit malleable and warpage can be corrected to some degree by bending and twisting the still-hot blade. An experienced blacksmith will not rely solely on corrective measures but will anticipate warpage and create a curve or twist in the opposite direction when forging to compensate in advance of quenching. This takes skill and experience, and even then, some rejects are unavoidable.
Chemical alloys like chrome, molybdenum, and tungsten greatly reduce warping and the risk of cracking.
None of this is mystical, but tools made from plain high-carbon steels such as Aogami steel and especially Shirogami steel require more skill and experience than those possessed by factory workers, much less Chinese peasants, so mass-production is nearly impossible, labor costs are higher, profit margins are smaller, and advertising budgets are non-existent. No wonder such tools get little attention from the corporate shills in the woodworking press.
While modern chemistry has unveiled the mystery of steel, it has only been during the last 60 or 70 years that metallurgical techniques have been developed making it possible to understand and control steel manufacturing.
The manufacture and working of steel are still magical processes that are the foundation of modern civilization. Make no mistake: without steel and the skill to work it, human life on this planet would be short and brutal.
If you have good sharpening skills but haven’t yet tried chisel or plane blades made from Shirogami, Aogami or Asaab K-120 Swedish steel, you’re missing a treat.
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