This review consists of :
The Naniwa Superstone are synthetic (man made) waterstones using a resin bond which are promoted based on the similarity to natural waterstones and the level of finish :
The Naniwa Sharpening Stones / Super Stones in the finer grits are the best for honing. With no other stone can one achieve so fine an edge.
However while they are often strongly praised, they are also strongly criticized, ironically enough for the same features that make them praise worthy under different perspectives :
One of the things to realize here is that often in stones, just like with steels, there are pairs of attributes which can not often be increased together. Making a stone cut faster tends to happen by making the abrasive more coarse or less likely to break down. This tends to make the scratch pattern more coarse. A very hard stone also will not self-condition and needs to be periodically recut or have the surface broken by extreme pressure to release fresh abrasive. As noted by Stu from TFJ :
What it does to blade edges is something that needs to seen to be believed. It is however an extreme example of good finish at the expense of speed and ability.
This is rated as a coarse stone, recommended for removing damage from the edge of a knife and in general significant shaping and removal of material. The abrasive rating is given as :
A quick check under 50X magnification shows a particle size in good agreement with the listed size. The distribution also appears to be fairly consistent which would be expected as this is a fairly high grade / expensive stone.
It also doesn't have a very open structure which is likely why it doesn't need to be soaked as water doesn't easily penetrate into the stone but just beads on top. It appears to have tightly packed abrasive with some larger opening holes periodically distributed.
It is however difficult to get high quality images of the surface as it would be interesting to see if there was any difference for example between the resin bond of the King stones and the Naniwa Superstones. The Kings are often described as similar, though softer, and full-soak stones which would imply they have a much more open structure and/or a lower bond/abrasive ratio.
This isn't an inexpensive stone and it shows in the manufacturing. Unlike inexpensive stones which can often have issues with problems regarding :
The Naniwa is ready to be used as-boxed with no modifications and immediately with just a little wetting :
An interesting comparison in terms of finish is seen when the Naniwa 400 Superstone is compared to the Bester 700. The Best is a similar coarse waterstone but aside from that one aspect, it is a fairly different abrasive.
The Bester Imanishi stones are described as a ceramic stones. This is one of those odd labels used to describe abrasives. All abrasives (alumina, silicon carbide, etc. ) are ceramics. It may refer to the type of bond used as they are fairly hard for waterstones. However finding exact details of stone manufacturing isn't trivial, especially when they are manufactured overseas.
The stones, being relatively hard, do not wear very quickly. One should allow them to soak for at least five minutes before use. The coarser stones, to cut as quickly and easily as they are capable, will often need another short dip in the water after a few minutes of use.
Taking a look at the surface of the stones, it isn't obvious there would be a significant difference in the scratch pattern the stones would produce. However in practice the Naniwa and Bester produce two completely different finishes.
To examine the finish produced, a base surface was needed to allow ease of examining the scratch pattern. A 1095 blade, a standard #1260 Mora was prepared to a near mirror surface :
This left the knife with a highly reflective surface, near mirror. As the surface is so smooth then it shows any scratch pattern very well. The #1260 Mora was chosen simply because it is so easy to polish as it has a low volume of carbides, no alloy carbides and in the Mora it is typically only moderately hard 59/60 HRC.
The difference in finish produced by both stones is dramatic :
The reason for the difference in the grinding pattern is simply due to the way that the Naniwa Superstone will generate a slurry which is colloidal meaning it stays uniformly thick and doesn't settle. This fine very mud which breaks down quickly from the surface of the stones is likely why it has the very distinctive traits :
This finish is often one which is desired by those that use/sharpen traditional Japanese knives.
Note the image on the right which is of a Yanagiba which was ground on the Naniwa Superstone. It produces that strong contrast in the laminated construction which is often desired by those that use such knives.
When you look at a traditional laminated Japanese blade you may notice that the different materials, the soft iron of the jigane or body material, and the hard carbon steel of the hagane or cutting edge steel each have a distinctive metallic sheen to them. Many times the soft iron backing metal looks dull and irregular in its granular composition when viewed next to the bright polished refined cutting steel portion of the blade.
This contrast is found to be enhanced or even exaggerated if the blade is honed on a traditional Japanese water stone known as tennen toishi, awase toishi or awasedo. Conversely when the same blade is honed on a synthetic manmade water stone the contrast between the hagane and the jigane will be noticeably lacking and the sheen can look uniform and shiny thus giving the bevel of the blade the look like it is all made out of one type of steel.
The difference between the very soft steel used on the blade body is in stark contrast to the high polish on the very hard steel which forms the edge. This contrast is obviously aesthetic in nature, a full mirror polish would in general enhance cutting ability (and increase corrosion resistance) slightly. But for traditionalists, showing the nature of the construction is often of importance and this stone does it well.
This very hazy, "shot peened" type finish has a very interesting application in regard to how the apex is formed by the Superstone and does it produce a dramatic difference there compared to other stones similar to how it produces a very different visible finish on the flats.
Note to the right two shots of the apexes of two knives, again formed with the Naniwa Superstone and the Bester 700. Now it is obvious that the coarse and linear scratches of the Bester go right to the apex and they make it form into a more jagged, saw like edge. The Naniwa forms a much more straight line apex which is far more even.
But here is the interesting part :
the apex naturally forms that way. However with the Bester then standard burr minimization had to be used to form that fairly clean apex :
This ability of the Naniwa Superstone 400 is so strong that it can be used directly to minimize the burrs and it makes a very great prep stone to set the edge for finishing with a micro-bevel.
However, while it works well as a prep stone, it isn't so great in setting the final micro-bevel. In regards to finishing the apex in that last step, the natural tendency of this stone to produce a thick slurry tends to round over / smooth out the apex
The very apex of the edge is of course ploughing through that very fine silt-like slurry which grinds the apex back flat as it grinds the sides of it down. This does make it non-trivial to actually use this stone to form a sharp apex though again it is great for burr removal/minimization.
The final micro-bevel and apex finish can be produced with the Naniwa and generate a decent sharpness, but requires a little technique :
In general though, unless a challenge is required, a more sensible approach is to use the Naniwa 400 Superstone to form the edge including grinding to an apex with a minimized burr and then switch to a harder stone which doesn't generate a thick slurry to set the apex.
Grinding a basic kitchen knife (Everday Essentials Chef's knife) to form an apex on a narrow bevel under low pressure :
The amount of passes to form an apex with the Naniwa and Bester :
The cutting speed with low pressure is similar which would be expected as the grit size is similar. However there is a very critical point here which is this is really pressure sensitive. The Naniwa is a soft stone and is not suitable for higher pressure. Note in the video to the right by Dutchbushcraft, when much higher force is used on the Superstone, in this case the 220 version, then two things happen immediately :
Now in general, a thick slurry doesn't actually increase cutting speed. There is this belief often in the knife industry that it does, but this is false. Three body abrasion in general (rolling abrasives) is very slow compared to two body abrasion (fixed abrasive). This is mainly because an abrasive which can move can do so instead of cutting.
As the Naniwa is shedding grit heavily under very high pressure it will not gain the expected increase in cutting speed at high pressure as would be expected from the Archard equation. The rate of abrasion (Q) is proportional to the load applied (W) and the sliding distance (L) :
as the Naniwa Superstone break down under low pressure they are not ideal choices when high cutting speed is a critical demand.
The Superstone doesn't require a soaking, it can just be sprayed with water and used, however a very light soaking is of benefit (a few minutes) because otherwise the surface dries continuously during sharpening.
However, as is common with a lot of traditional Japanese stones, there are warnings that come with the stone to avoid :
In general, it isn't that uncommon to find reports of cracking of these stones. They are not even close to the robustness and durability of the vitrified bond oil stones which are near invulnerable.
i recently bought an 8k hone to touch up my razors. and i got all set up to start honing and after the first pass i made i noticed a small crack in the hone.
Hence why a lot of people who have the very expensive versions will typically take care to minimize change of cracking :
This is one of the main criticisms of these and similar stones by wood workers who often complain they are fragile in nature compared to a basic India or Norton Crystolon.
The Naniwa forms a slurry readily and it therefore resists loading and thus the surface doesn't tend to need to be cleaned or recut. However as with all waterstones it will wear and does so at a much more rapid pace than the traditional natural stones (Arkansas) or the Norton India type oil stones.
Now uneven wear can be minimized by altering the grinding pattern on the stone, Murray Carter has talked about that extensively, however at some point wear does set in and the stone has to be flattened or else the wear will start increasing the angles by adding a curvature.
As this stone has a fairly soft bond it is very easy flattened by another stone, there is no need for a special flattening stone, though a DMT plate works well. However the simplest solution is just to lap it against another stone and vary the grinding passes so as to even out both surfaces. Flatten the surface and then round the corners.
The interesting thing about this stone is that given the way it breaks down easily under very low pressure, it constantly releases fresh abrasives and thus it can easily cut even the hardest and the highest carbide steels. Note the blade on the right is from 121REX at 69/70 HRC . 121REX is among the highest carbide high speed steels and there is no problem grinding it.
Now there is often advocation of use of silicon carbide for grinding such steels, but in general the bond type is more important than using alumina vs silicon carbide. Silicon carbide is harder than alumina, but both are softer than vanadium carbide and harder than all the other carbides in steels 2 :
As a point of comparison, this stone is very similar to a King 1000 in many aspects which also produces that fine style of mud, that hazy finish, and that natural burr minimization. The Naniwa is just harder than the King, slower wearing and doesn't require soaking.
Comments can be emailed to cliffstamp[REMOVE]@gmail.com or by posting to the following thread :
and/or the YouTube Playlist for Abrasives/Sharpening.
Most of the pictures in the above are in the PhotoBucket album.
1 : Conversion Chart Abrasives - Grit Sizes
2 : ASM Speciality Handbook, edited by Joesph R. Davis
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