Ara-toishi, or coarse grit stones, are usually top strata (ara-pin) stones, and typically some form of sedimentary sandstone, that are typically used as the first set of stones for dull blades. They typically range from ~300-<1000 grit, and are ideal for chip removal, bevel setting, or even slight profile alterations. Depending on the intended use of the blade, such as butchery or vegetables, some users may even stop sharpening on some of the 'higher' grit ara-toishi and be fully satisfied. Since they are a top layer stone, they are quite porous, very muddy, and efficient, as well as easy to excavate and thus cheap and easily accessible to buyers. A downside is that could potentially contain toxic inclusions, typically very hard concentrations of quartz (or silicon dioxide), or even 'debris' like pebbles, which could damage a blade during sharpening, thus a reliable source is required to assure that the stones have been inspected and and pass muster that there are no potential toxic inclusions. Synthetic stones have largely replaced ara-toishi given their guaranteed lack of toxic exclusions and set grit levels with very hard abrasive particles, as well as relative affordability. However I have often found quality ara-toishi to dish less and require less lapping (dishing is when the stone erodes slowly from sharpening and needs to be flattened true again by a lapping plate to maintain true angles). Add in the beauty of ara-toishi, and I often find myself reaching for them when I'm doing light repairs or bevel setting on high quality steel.
Estimated Grit: 300-600
Weights and Measures: 220x66x49mm; 1741.5g; 6.8g/cm3
Appearance and Texture: From afar, one of the more bland stones out there, with what appears to be a cold dull gray. However upon much closer inspection, the seemingly solid gray is actually composed of thousands of blueish-gray and off-white specks, even the occasional purple-hued speck. Inspiring to know that there’s always more going on that what initially meets the eye. The texture is what one might inspect for such a low grit stone - the surface is somewhat rough, indicating a very effective stone at removing metal quickly. With the addition of water, it turns a very dark gray, but more closely, the blue and purple specks become a bit more pronounced.
-Sharpening Experience and Results -
SS: The omura is extremely efficient at moving metal on softer SS, with a burr forming even on a single pass along the first edge, indicating its purpose of minor chip removal, bevel setting, even slight tip repair and profile alterations. Tactile feedback is also not surprising, making for a gritty feeling that resonates through the blade, also giving way to an unpleasant scraping sound; but again, this all means it’s doing its job quickly. It’s so quick, that water management is of little concern for such a porous stone for quick bevel setting. Because the stone gripped so much steel, a fair amount of swarf formed even with such few passes. The edge results are surprisingly sharp, relatively speaking, and could cut paper with proper honing, although I wouldn’t feel ready to put the edge to work. It definitely needs an additional stone or two to finish. A visible scratch pattern, indicating coarse abrasive particles, was clearly visible on the edge.
Shirogami: A much different experience than the soft SS, as the hardness of the steel prevent the stone from grabbing as much metal, leading to a much smoother tactile feedback, and reduced noise. This also makes for less efficiency, although relative to other stones, the burr formed after 2 or 3 passes on each side. I likely would turn to a more aggressive synthetic stone for minor chip removal, etc, but it could certainly be done on the Omura in a few minutes. Much less swarf formed vs the SS, and for more effectiveness, users may find building The edge was indeed sharp after a quick deburring, and could easily cut through paper (ahh, the magic of shirogami). I would expect some users who primarily prepare soft fruits and veggies may be satisfied with this edge, although it likely wouldn’t last too long. A visible scratch pattern was visible on the edge, albeit slightly less deep than the softer SS.
Aogami: A bit similar to the shirogami experience in terms of feedback and noise, but even less metal was removed given aogami’s increased toughness from its alloys. Even still, if you had several minutes, light repairs and thinning can certainly be done. The finished edge was less keen than the shirogami, and will require at least one more stone for satisfactory results. Exhibiting its wear-resistance. the edge on the aogami presented the 'shallowest' scratch pattern relative to the other steels.
Conclusion: The Omura is certainly an effective stone, even against wear-resistant steels, and certainly earns its place in a well-rounded tennen toishi lineup. Given they are cheap and abundant, trying one out for yourself is worth the investment to get an understanding of how effective natural stones can be at removing metal. Given that this is typically the first stone in a restorative session, the edge results will typically need another 1-3 stones for most users to feel satisfied.
Estimated Grit: 400-800
Weights and Measures: 200x62x45mm; 1364.5g; 2.5g/cm3
Appearance and Texture: This is a very intriguing stone, with whirls of goldenrod, browns, yellows and gold. With the addition of water, these colors become more contrasted and pronounced. There are visible poc marks throughout, which speaks to its porosity, although they aren’t very deep, and they don’t negatively affect the sharpening performance. Considering that this is a very coarse stone, the surface actually feels relatively soft and smooth, with a little dusty texture, almost as if it were a big block of chalk. This is usually an indication of a muddy stone. Although most sharpeners do not give the density of their stones, one way to guess if a stone will be muddy, is to look at its density. This natsuya is noticeably less dense than the omura, which suggests that the spaces between particles is large and can more easily be broken, thus freeing up abrasive particles quickly, leading to mud, which ended being the case.
-Sharpening Experience and Results -
SS: The theory that this was going to be a muddy stone ended up being true as it made extremely quick work of the SS, forming a burr in one pass on each side thanks to so many loose abrasive particles. The softness of the stone was pleasant, maybe even a little too soft, as I had to watch my angle to make sure I wasn’t too high that I would gouge the stone. The noise and feedback were marginally less abrasive to the senses than the omura because of the softness, but still not pleasant. The edge was extremely toothy, to where another stone would be required to finish, even for those who like very toothy edges.
Shirogami: Again, a very different experience with the shirogami VS the SS - smoother feedback, almost slick, less swarf build up, smaller and slower burr formation. While the SS edge yielded something that would need to be taken up at least another stone, the edge result on the shirogami was a relatively more refined toothy edge (but still quite rough), that could easily cut through paper after some quick deburring. Those who like their edges just refined enough to work under most circumstances could be satisfied after using the natsuya and honing on a quality strop.
Aogami: The feedback on the natsuya was ‘slicker’ than the feedback omura with aogami. Slickness is usually an indication less metal removal since the steel is not being ‘grabbed’ and efficiently removed by the stone, which becomes more common as you progress into higher and higher grits. This was the result with the aogami, has it took the longest to form a burr (as it almost always will vs SS and shirogami), albeit still quickly given the softness and grit of the stone. This can be explained by the alloys in aogami such as tungsten that really do not like to be broken up. Even still, the muddyness and low grit of the natsuya eventually gave way to a solid toothy edge, that again, I would prefer to take up to another stone.
Conclusion: This is an interesting case where the grit of one stone, the natsuya, is likely a bit finer (albeit only slightly) than a coarser grit stone, the omura, but is actually (marginally) more efficient because its softness yields a larger amount of abrasive particles to work with; again, the not-so-straightforward world of natural stones. While minor chip removal and tip repair could be done with this stone, I’d likely leave that role for the slightly more firm omura, as such repairs would shorten the life of the soft natsuya, but I’d likely reach for this natsuya rather than the omura for simple bevel resets. I often find natsuya to be more abundant and affordable, so getting a couple is not a bad idea, and they all tend to be unique and pleasing to look at. A fun, muddy, efficient stone.
Amakusa Aka Torato
Estimated Grit: 800-1000
Weights and Measures: 198x71x60mm; 2269g; 2.7g/cm3
Appearance and Texture: Again, a beautiful stone, this time with the aesthetic denotation of ‘aka, which means red (or crimson, brown, etc), and ‘torato,’ which means, tiger. And indeed, the layered wisps of burnt orange, browns, and grays, give an impression of a tiger in motion. The base color is a beige-ish off-white color, with blue-ish gray specks, off which the same color line runs through the stone, and is reminiscent of a river. The texture of the stone is smoother than the former ara-tosihi, and suggests a slightly higher grit and increased firmness.
-Sharpening Experience and Results -
SS: While the omura and natsuya were extremely efficient, with a large dose of aggressive tactile feedback, leaving a premature edge on SS, this amakusa is a step in the direction of balance - it’s still very efficient on SS, has a smoother tactile feedback, and provides an edge that could be used with little trouble. The feedback was definitely more pleasant than the omura and natsuya, as the amakusa is a bit higher grit, and firmer. The firmness reduced the muddyness vs the former stones, slowing its efficiency a smidge, but combined with a slightly higher grit, the feedback was much less gritty. The slightly higher grit gave way to a more bit more of a tuned edge, but still providing a good amount of bite. The burr was small and fine, and could largely be removed by some hand stropping. The edge could be ideal for some users for firmer fish (as the knife used this week is a very flexible fillet knife), where some bite would be needed to cut through some fibers, but softer fish, especially where perfect presentation is required, would likely take the edge up another stone or two; still a very useable edge. For others SS knife types, most applications could be met to a good degree.
Shirogami: The perennial theme continued, as the shirogami, with its increased hardness, took twice as long to form a similar burr, and resulted in an edge that left more to be desired. Its firmness in combination with the hard steel, reminded me of stones a level or so higher than this, and the knife was almost starting glide across the stone as felt in harder stones, but with enough feedback to know clearly know where I was along the edge.The edge was lackluster, like an edge off a subpar 1000 grit synthetic. It seemed like iit couldn’t decide if it wanted to go lower in grit for a tootheir bite, or higher for a keener edge. My tastes prefer edges on the keener side of things, so I would be inclined to take it to another stone. The burr was relatively fine, but I still needed quite a few passes with my hand to get any real deburring going, but pulling through cork removed it in two swipes after the handhoning.
Aogami: Aogami, especially on the Zakuri workhorse gyuto used this week (which is thick behind the edge) and this stone, don’t really mix. Since I start with a dull edge on these Ara toishi, progress forming a burr took around three passes on each side. Beginners typically find a thick convex grind and a firmer stone to be difficult, as the knife can roll on a harder stone with ‘slippery’ feedback, and I had to watch my angles a bit more than I usually do. Again, the edge was lackluster, and I would consider dropping down in grit to thin out a new bevel, and take it up a couple stones from there. I knew not to waste my time handhoning, and had to deburr on the stone and cork.
Conclusion: While the results, specifically on the aogami, weren’t quite satisfactory (not bad by any means, just not exciting), I love this stone for SS. It’s still efficient, while providing a useable edge, that with a more proper honing than hand honing, could perform well for most tasks. This stone has the perk of being a lighter color (a slightly off-white), and whiter stones allow the sharpener to see the metal removed, giving a better sense of progress and position on the stone, which is very useful for beginners. I enjoyed the firmness of the stone, as I prefer firmer stones, and those learning to work with harder stones could certainly look to amakusas like this one for help with that. The additional aesthetic beauty, especially with the ‘tiger’ theme, makes it a fun stone that I use often with SS. So for those who mainly use SS, and are looking to dip their toes into the natural stone waters, this is a great option, as amakusas like this are readily available and relatively affordable.