NSK Kogyo Ltd. Diamond Stones are unlike anything we have ever used — and we have used a looooot of stones over the years. The NSK stones are profound in their incredible efficiency, hyper consistency, and extreme longevity. Masterly formulated and developed over nearly two years by Ivan Fonseca of Tosho Knife Arts directly alongside NSK Kogyo, these stones are as dialed-in as you can get. We have no doubt these stones will have a large impact on the global sharpening/polishing market — they feel like they do the work for you and perhaps even make you seem better than you are - they are like magic!
With a variety of hardness levels and sub-hardness levels targeted for different tools, steels, and user-preferences, the wide library of options from NSK is impressive and likely means there is something for your particular needs. One of the main benefits of these NSK stones is the fact that they are extremely long-lived stones that do not dish even after many, many uses. Even with professional rates of wear, these stones will last a very long time. While it is very difficult to quantify how many knives and tools can be serviced over the lifespan of a single NSK stone, it is very likely in the many hundreds, perhaps even in the thousand+ range. Additionally, further adding to their already extreme longevity, most of the stones are over 3.5mm thick, typically much thicker than most other diamond stones.
We are honored and excited to offer these amazing stones to you - we are confident you will love them as much as we do! For more information you can expand our notes below, or watch the man himself, Ivan Fonseca using and describing NSK stones here.
The sharpening experience is... incredible. The feedback has somewhat of a subtle, constant "grip" texture, allowing you to better perceive what portion of the blade you are working which reduces the chances of slipping or making an incorrect stroke. Since the diamonds are in the unique matrix of the stone and do not break apart like synthetic stones, the tactile (and auditory) feedback is much more pleasant and comfortable. Every single stroke feels like the last, providing rhythm and confidence. Given the small surface area of a knife's edge, NSK stones cut sharpening time to a substantial degree.
In terms of polishing there are no other stones that we've come across that can compete with these NSK stones, seriously. Even at the coarsest grits the scratch patterns are not "deep" like you may find with other coarse synthetic stones or diamond stones where the diamonds protrude out from their underlying plate. So while the coarse NSK stones are removing metal at an impressive rate, the finish they leave is always consistent and they feedback is very mellow.
Despite most of the NSK stones being on the harder side, the stones do not ever cause unwanted scratches, which is otherwise a constant worry when polishing on hard stones. Since every single scratch is the same width and depth it is very easy to see contrasting scratch marks from a previous stone which allows you to easily track the progress of your work - something very important in polishing. Additionally, since the stones don't dish, it is a lot easier to get hyper crisp, straight Shinogi lines and other bevel changes.
Nagura are also available and will help further increase speed of metal removal, and allow for unique grit combinations when polishing since you can easily use nagura of different grits on the stone at hand.
The orientation, composition, and quality of the diamond matrix is tuned to remove metal at an astonishing rate. Since the stones don't really wear, the surface is always flat. These wear resistance properties speed up longer sessions since you don't have to constantly pause and re-flatten the surface like standard synthetic stones, and even other diamond stones. Additionally, the NSK stones' constant flatness maximizes surface area contact between the stone and the blade, meaning you are working on as much of the knife as possible with every single stroke, leading to optimized efficiency. Those daunting whole-blade repair/refurbishing/polishing projects that have been gathering dust on your shelves can now be completed in far, far less time, not to mention with hyper consistent results and a more enjoyable experience in general. The time it takes tuning up your edge on the line during a rush is cut way, way down. The frustration of short-lived edges in any application is alleviated thanks to efficiency of NSK stones. It actually takes a minute to get used to the rate of removal despite the fact that the feedback is so mellow, it almost feels like you're not doing much work - so start slow.
We encourage users to purchase the specifically formulated flattening/dressing stones for best results when the time comes to flatten as they are purpose-built to work on NSK sharpening stones and are able to combat the wear resistance of the sharpening stones. The flattening stones are also incredibly useful for lapping natural stones without leaving any scratch marks that you may find when using other diamond plates. All NSK sharpening stones come with a small "wafer" piece of diamond stone to ready the stone's surface for optimal efficiency after having used a flattening stone.
NSK stones come with chamfered edges, but we encourage users to round them over throughout the wear of the stone. Do not use any flattening stones that may cause scratches into the surface. Do not soak more than a few minutes, NSK stones are pretty much all splash and go. Wash and clean all stones after use, and let them dry in a slow, controlled manner away from direct sunlight. All stones come in a clearly labeled, handmade kiri wood box and beautiful packaging.
Oboro Knife
The newest NSK series, Oboro Knife was designed specifically for kitchen knives, and are very effective on a wide variety of steels for a wide variety of services. The abrasives in Oboro Knife tend to cut deeper and faster than other NSK lines, thus they are the most ideal series for bulk removal and full-blade servicing such as thinning, repairing, and reprofiling. Since they are harder stones, Oboro Knife is helpful when trying to get crisp, straight lines like Shinogi on single bevel and wide bevel knives. Recommended for seasoned to advanced users.
Oboro Knife grits are: 200, 400, 800, 2000, 4000, 6000
Oboro Tool
The hardest of all NSK stones, Oboro Tool are ideal for wide bevel, push-cut tools like chisels, planes, razors, or working the Ura of single bevel knives. Oboro Tool stones are the most similar in feel and finish to natural stones. Being similar to natural stones, they are graded the same way as natural stones rather than exact, specific grits like all the other NSK Kogyo series are. Recommended for seasoned to advanced users.
Oboro Tool grits are: Chu-Koma (~#2000), Chu-Shiage (~#4000), and Shiage (~#6000)
Kyokuha
The original NSK Kogyo diamond stone series, Kyokuha are built for ease of use and compatibility with a wide variety of steels from carbon, stainless, powder, even tool steel. It has a large selection of grits to fit almost every user's needs. These are the softest of the NSK series and probably easiest to learn sharpening and polishing. Recommended for beginners and seasoned users, or those who simply prefer softer stones.
Kyokuha grits: 200, 300, 400, ~500 to ~600, 800, 1000, 1500, 2000, 3000, 4000, 8000, 10,000, and 16,000
Hakuto 1
The hardest of the Hokuto series, and just a little softer than Oboro Knife. These are ideal for those who prefer firm, but not really hard stones. They can be used in many of the same ways as Oboro Knife such as bulk removal or other whole blade work; best of the Hakuto stones for straighter lines. Recommended for advanced users.
Hakuto 1 grits: 200, 400, 400S, 800, 800S, 1500, 3000, 6000, 10,000
Hakuto 2
Medium hardness, they are ideal for creating softer bevel changes and finishing full convex grinds. Given the available grits are only medium to high grit, Hakuto 2 stones are best left for use after initial, coarser work has been completed. Recommended for advanced users.
Hakuto 2 grits: 3000, 3000S, 6000, 6000S, 10,000
Hakuto 3
The softest in the Hakuto series, they are the most similar of the Hokuto stones to feeling like soft, muddy natural stones. Like Hakuto 2, they are ideal for creating softer bevel changes and finishing full convex grinds. Given the available grits are only medium to high grit, Hakuto 2 stones are best left for use after initial, coarser work has been completed. Recommended for advanced users, or for users who prefer the feel of of natural stones that are not as hard as Oboro Knife.
Hakuto 3 grits: 3000, 6000, 10,000
Flattening Stones
Although all NSK stones are very wear resistant, these flattening/dressing stones are specifically formulated to counter the wear resistance and flatten at an impressive speed. They also work very well on natural stones as well, and the higher grit flattening plates will leave a scratch-free surface unlike many other diamond plates. The flattening stones are slotted to eliminate suction when rubbing against the sharpening stone. The flattening stones are also the best tool to keep the edges and corners of the sharpening stones rounded.
If needed, coarser flattening grits can initially be used on higher grit sharpening stones to remove material quickly, but it is recommended you then condition the surface of the stone with a higher grit flattening plate before use in order to prevent overly-aggressive surface. Each grit of the flattening stones can be used on several different grits, see recommended grit ranges for each flattening stone below.
Flattening grits: 200, 400, 600, 1000, 3000, 6000
Recommended use: Flattening grits from 200-1000 can be used on all NSK sharpening stones up to 1500 grit. All NSK sharpening stones with grits above 1000 should ideally be flattened with a grit as close to the stone's grit as possible. For example, a 3000 grit sharpening stone should be flattened with grits 3000 and above. If you do not have the ideal flattening grit for the sharpening stone at hand, you can condition the surface post-flattening with the included wafer, or with the available diamond nagura.
Nagura
Nagura are very helpful in both increasing the efficiency of metal removal by adding grit on top of the stone, but also in creating unique, multi-grit slurry combinations important for polishing purposes. They can also be used to condition the surface of the sharpening stone after using a flattening plate or after extended periods of sharpening to remove particulate.
