Whether sharpening a knife, honing a razor, or blade polishing using a whetstone to get the process done is a time-honored tradition. To accomplish this task, many people prefer to use synthetic whetstones with clear grit ratings and consistent results. Others prefer using natural whetstones – as has been done for thousands of years. There is no reason someone cannot use both with each requiring different proficiencies and skills to use well. I am documenting the information I have learned as I explore these topics on this website. My goals are to help others grow their own knowledge and explore the hobby I am passionate about.
Overtime, I hope to explore many different stones from all over the world and have the opportunity to use them and report on my experiences. I hope you find the following information enlightening. Should have you have any information to add or input about the items presented, please never hesitate to contact me.
How a Natural Whetstone Works & Natural Whetstone Slurry
Why are Japanese Natural Stones so Prolific?
Synthetic vs Natural Whetstones
Why use Natural Whetstones?
In-depth Information on Japanese, European, and American Natural Whetstones
How a Natural Whetstone Works & Natural Whetstone Slurry
A whetstone at first glance is a fairly simple object. An abrasive brick you run the blade over to remove metal. In many ways this is correct. However, it is missing some of the microscopic workings of the whetstone which affect how the metal is removed from the blades edge. Natural whetstones often benefit from the use of slurry (sometimes called togidoro or mud) to speed up or augment the sharpening/polishing process. Slurry is created by rubbing one small stone (sometimes called a nagura, slurry stone, or rubber) on top of your larger base stone. In modern times, this can also be done with a tool we call a diamond plate / diamond nagura which is a flat aluminum plate with diamond grit embedded onto its surface. Regardless of the tool used to generate it, slurry is a mixture of water with the binder and abrasive created from both the base stone and nagura rubbing together. If using a diamond plate, the slurry will be purely from the base stone itself.
As the blade is worked on the surface of a stone with slurry on it, the edge and bevel of the blade are both impacted by the grit in the base stone itself as well as the abrasive grit suspended in the slurry thus speeding the process up. Slurry can also help in suspending metal pieces that come off the blade during the abrasive action (called swarf) from the surface of the stone. This avoids the stone “clogging” where the metal pieces embed themselves in the pores of the stone which in turn keeps the stone performing for longer before it must be surface refreshed. Without slurry, stones will usually (especially for harder/finer finishing stones) remove metal slower but at a finer level. Slurry performs very differently based on the make-up of the stone itself, and some initial research must be done to have an understanding of how aggressive or fine the slurry will be before using it (this is especially true for Novaculite stones such as Arkansas, Charnley Forest, Llyn Idwal, Cretan/Turkish Stones, etc.)
Natural Whetstones also offer us the ability to do “surface conditioning” or “surface refreshing” to achieve different performance levels. This is where we treat the flattened surface of the stone with sandpaper, rubber/nagura/slurry stones, or some other abrasive to set up the surface to perform in a certain way. If you want the stone to act softer or faster cutting, you may surface condition with a 200-400 grit sandpaper. Alternatively, if you want to finish a razor you may surface condition with a 1000-2000 grit sandpaper or fine nagura/rubber/slurry stone. Because the grit in Natural Stone isn’t as hard as the grit used in synthetic stones, we can use this condition surfacing to unlock different behaviors from the single stone. If you tried to do this with a Synthetic stone the performance would not change as the abrasive compound (aluminum oxide) is so hard it will perform “normal” whether the surface is conditioned, refreshed, or just flattened. Usually the term “surface conditioning” is used when you treat the stone before using it, where as “surface refreshing” referring to treating the surface of the stone after it has changed attributes through use (either by using up the abrasive on the surface of the stone or by the pores in the stone becoming clogged with swarf) thus “refreshing” the surface of the stone to its previous performance.
Some whetstones are coarse enough or soft enough that they will generate slurry on their own without the use of a rubber/nagura/slurry stone. This attribute is often referred to as self-slurrying stones. For these stones, you will not be able to surface condition to achieve different performance as the stone will readily refresh its own surface. Soft stones tend to be less suitable for higher level sharpening or honing performance (this is not a hard and fast rule) but can be very useful for faster kitchen knife level sharpening and specifically are very valuable for polishing.
Why are Japanese Natural Stones so prolific?
When starting to look at the natural stone spectrum, it is quickly established that Japanese Natural Stones are some of the most common and desirable stones. Even looking at the spread of information on this site corresponds with that reality. Japan is home to a large portion of easily accessible stone suitable for whetstone production. This plays one of the factors in its popularity, a lot of it is available. However, and maybe more important, is the catalogued and studied nature of stones in Japan. Unlike other areas of the world which may be known for a single stone (Belgian Coticule, German Thuringian, UK Tam O Shanter, etc.) Japan has a storied history of testing and orally passing down the knowledge of different whetstones and their properties. The UK is probably second inline conceptually, but recorded information and knowledge of those stones still pales in comparison when compared to Japan regarding their natural whetstones.
If you are looking to only use water as your honing medium, then JNATs are particularly attractive for their range of functionality and high performance with water. This is especially true with razors, where fine JNATs and Thuringians produce the best results with water only. However, many stones can get extremely close to those performance levels for a fraction of the cost – and even more can achieve or beat those same results when glycerin or oil is considered as an alternative honing solution to water.
Lastly, very few other natural stones compare to JNATs when it comes to blade polishing. The ability and range of JNAT stones to polish a blade is far above most other regional natural stones, this combined with the well-kept recorded history of Japan’s natural whetstones allows for a predictable result when it comes to polishing performance.
Synthetic vs Natural Whetstones
There are many differences between natural and synthetic whetstones. These topics include price, grit, grit type, binder type, and more. We will start with the makeup difference between the two. Natural whetstones suitable to be whetstones are formed by geological changes within the earth’s crust over millions of years. These whetstones are primarily comprised of a clay-like binder with a natural abrasive pressed together within it. Often these stones will then undergo some metamorphic process through heating and compression. This claylike binder can comprise of many different substances and take many shapes. Japanese whetstones for instance look like platelets or flakes. Other stones can be formed into a matrix of crystals such as the Arkansas whetstones where the formations are oblong or round crystals semi-fused together. These shapes are naturally made, so difference in size, shape, and performance is to be expected even when they share a commonality. This is part of what gives natural whetstones their unique properties. While the abrasive within the binder does the majority of the cutting, the binder material can play a huge role in how the abrasive rubs against the surface of the blade thus impacting how it cuts/polishes.
Synthetic whetstones are manmade products with a synthetic abrasive suspended in a resin binding agent. The abrasive is going to take the form of a grit which is highly uniform and will be easily released from the binding agent. This quick release is one of the first distinct differences between the natural and synthetic whetstones. Synthetic whetstones will typically break down much quicker than natural whetstones but will also create their slurry much easier.
The abrasive in natural and synthetic stones are different in composition and hardness. Natural stones are using a form of silicone dioxide (silica) which is only a bit harder than the hardened steel you are sharpening/polishing. Often you will hear people claim that natural stone slurry breakdown as you use them. There is no evidence this is true, however, there is evidence though that the silicon dioxide is getting smoothed out as you sharpen due to the similar hardness. This smoothing results in the slurry acting as a higher grit and feeling broken down more. A synthetic stone typically uses silicon carbide or aluminum oxide. Both of these substances will be harder, more jagged in shape, and not smooth out when compared to silicon dioxide. This is one primary reason why synthetic whetstones cut so much faster than natural whetstones and do not have the same range that natural stones do. For this reason, a synthetic progression of stones will require many more steps/stones than a natural progression – but each step will be moved through faster.
Why use Natural Whetstones?
There are many reasons someone may choose to use Natural Whetstones over Synthetic ones. Of these many reasons, there are a few specifically worthy of mention when considering the topic for yourself. When we sharpen or hone a blade, it is altering how the microscopic teeth (called feathers) at the very edge of the metal are formed. Regardless of how fine you sharpen/hone your blade, these feathers always exist and at the most minute level all blades are still “sawing’ their way through material.
When it comes to sharpening/honing, a benefit of natural whetstones is regarding abrasive particle being naturally uneven in their size due to how they are geologically formed. When used for sharpening/honing a blade’s edge, this varying size results in these feathers being of an ununiform pattern across the spectrum of stones. Of course, a finer stone will still make smaller feathers at the blade edge than a coarse stone, but the teeth will still vary a little between one another. This variety in the size of the feathers results them will wear at different rates rather than evenly all at once, allowing the knife or razor to stay sharper for longer than the uniform teeth created by synthetic stones. This is similar to why many saw blades use varied teeth size in their construction.
Additionally, the binder in natural stones is compressed and much stronger than those of synthetic stones. A natural stone will last much longer and dish out slower than most synthetic stones. A nice quality bench sized natural stone should last the average user a lifetime if not be passed along for multiple lifetimes.
A natural stone will also allow for more options regarding blade polishing whereas synthetics are often a poor choice for such work unless you are working up to a mirror finish. This is due to many factors, but usually relates to the binder composition playing a role in the polishing process as well as the softer silica abrasive used. It is very difficult (maybe impossible) to replicate the beauty of a natural stone polishing with synthetic stones.
There is also something to be said for the history of using natural stones. If you are someone who appreciates traditional methods and how it connects us to our collective pasts, natural stones have a special place. The smell of earth they release, the traditions and methods associated with them can be a very fulfilling experience. It is a personal choice though and not for everyone, but if it intrigues you, I suggest you try one out and have a chance to experience it.
In-depth Information on Natural Whetstones
The below sections lead to additional information regarding different natural stones, blades, razors, and honing methods. This entire website is a work in progress as a hobby and not a job for me. Please excuse its incomplete nature as it is a living document, forever expanding!