Natural Whetstones

by Sakai Ichimonji November 27, 2023

Although natural whetstones are produced in very small quantities, many people use them in search of a finish that can only be obtained from natural sources. We carry a range of them in our store and have some from incredibly famous places, and we're very proud of the selection we have from entry level to the most premium and rare.

Importantly though, they are measured somewhat differently from artificial whetstones. This blog will talk about the characteristics of natural whetstones in different regions and how to select one.

What is a natural whetstone?

Natural whetstones are treasures created from the Earth itself. That is to say, they are mined from the ground and mountains directly then cut into the appropriate size for use.

They are a naturally created stone that has formed for hundreds of millions of years through to the present age. These are mined from geological strata made of sedimentary rocks and tuffs.

The characteristics of these stones vary depending on the region where they're mined, influencing the final outcome of their sharpening process. For example, some may be suited more to a medium whetstone usage, whereas others will perform brilliantly as high end finishing stones to give a blade a unique shine that only they can provide.

Cherished by enthusiasts who seek to master their sharpening abilities, natural sharpening stones enhance the beauty of knives by delicately finishing the blade, showcasing an amazing surface on materials those knives cut through. If you want that "perfect" cut, look no further.

The Charm of Natural Whetstones

Some of the natural whetstones in our store!

Our rarest whetstones are in the shopfront, including one not for sale!

The allure of natural sharpening stones lies in the parts of it that remain elusive to us even today.

Created with a molecular structure different from artificial whetstones, natural stones undergo structural changes over time as they are used, resulting in a unique finish with every sharpening. In a way, they become better as they are used.

Therefore, the more a knife is sharpened, the better the finish becomes, with a slightly different outcome each time. It is precisely because there's no endpoint with these stones that knife enthusiasts love them.

The Strength Behind Natural Whetstones

A natural whetstone's strength is supposed to be an "excellent cutting taste".

Even with artificial whetstones, you can achieve amazing levels of sharpness if used correctly. In some cases, it may feel even sharper than a natural whetstone!

However, we believe there is a key difference between "sharpness" and "cutting taste."

Sometimes we talk about the "taste" behind sharpness. That is, we believe how something is cut can determine its flavour. We say that the true strength in natural whetstones is that they help you create and maintain a knife that cuts very well - and therefore impacts the taste behind food more greatly. Taste is also about mouthfeel, after all!

The Differences between Natural and Artificial Whetstones

The top side of a natural whetstone

And the bottom - note the marks in the stone that show how it may have been mined!

Let's explore and compare the differences between natural and artificial whetstones when applying them to the same kind of knife:

Natural Whetstone Performance
Scraping Performance	Spending a long time to sharpen slowly results in a superior edge Scratches on the blade are shallow Less likely to develop a rolled edge/tip Easy to remove a rolled edge/tip
Polishing Performance	Able to polish surfaces very well and make a deep luster Achieves an internal clouding effect that brings out the pattern on the blade
Finished Blade Performance	High precision due to a strong hardening effect of the blade edge Rust-resistant
Effect to Cutting Performance	Very good sharpness Creates an edge with longer retention Longer time between resharpens Increases lifespan of sharpened items

Artificial Whetstone Performance
Scraping Performance	Removes material from the blade quickly Leaves deep marks on the blade edge Prone to developing a rolled edge/tip Trickier to restore the original blade edge
Polishing Performance	Able to achieve mirror finishes Displays a white gleam
Finished Blade Performance	Lower final precision Prone to rusting
Effect to Cutting performance	Initial sharpness is very high Sharpness is lost quickly Sharpening takes more effort Shorten lifespan of the blade

Even though there is a distinction between natural and artificial materials, why is there such a significant difference?

The answer lies in the abrasive grains, the primary component of sharpening stones. You can read more about sharpening stones in general here.

Synthetic sharpening stones are primarily made with abrasive grain materials such as carbon (C) and alumina (A). These grains are hard and have sharp edges, causing them to grind excessively during use.

Even with high-grit finishing stones, scratches may remain, and a pronounced rolled edge can occur.

In contrast, natural sharpening stones have abrasive grains with rounded edges. With each time this stone is used, these grains break down into finer particles, resulting in shallower scratches and a more precise finish. This is why we say natural stones get better over time and usage.

Natural whetstones improve over time as they are used

Are synthetic whetstones inferior?

While the above might imply that artificial stones are worse than natural ones, that isn't the case. Rather, they have different purposes and objectives that they meet.

For example, synthetic whetstones have very high grinding performance, allowing you to sharpen faster. Additionally, as these whetstones are man-made they can be created for specific purposes, hence why there are many different grit numbers - in a sense, you know what results you will get and can select your whetstone accordingly.

Therefore, thanks to artificial whetstones you can get to your desired end result quickly - something that natural whetstones cannot do as easily.

Natural Whetstone Production Areas

Since natural whetstones are mined from nature itself (hence their namesake), they have been collected from various parts of Japan. Let's explore some of those regions below.

Name	Region	Characteristics
Omura whetstones	Wakayama Prefecture	Originally Omura whetstones are mined in the Omura region of Nagasaki Prefecture. As mining in Omura has stopped, they are now mined in the Shirayama region of Wakayama. This sandstone sharpening stone, with its mouse-colored appearance, has traditionally been used as a rough whetstone.
Hirashima whetstones	Nagasaki Prefecture	This sharpening stone is mined from the Toishi-yama stone quarry in the Hirashima region of Nagasaki Prefecture. It is a sandstone-based whetstone that produces a significant amount of sandy mud, making it suitable for use as a rough whetstone.
Aoto	Kyoto Prefecture	This is a medium-fine sharpening stone which is a little bit on the finer side, mined in the Tanba region of Kyoto. It's designed for intermediate sharpening, enabling a prolonged sharpness. The blade surface after use will show a beautiful luster, making this the best medium sharpening stone not only for sharpness but also for polishing Japanese swords.
Amakusa whetstones	Kumamoto Prefecture	This medium whetstone is still being mined in the Oyano area of Kumamoto Prefecture. They are classified by grade into "Joshiro (Binsui)", "Chushiro", and "Tora (Aka-tora)".
Iyoto	Ehime Prefecture	A soft, easy-to-sharpen medium-grade stone mined in the Iyo region of Ehime Prefecture. It was also used for sharpening Japanese swords.
Shiranakurado	Aichi Prefecture	A white medium whetstone mined in the Mikawa region of Aichi Prefecture. It has also been used for a long time as a nagura stone which creates a lot of liquid.
Awasedo	Kyoto Prefecture	The finest whetstones are mined in Kyoto, and this fine-grained finishing stone is the only one in the world produced exclusively in Kyoto. The characteristics of the stone vary depending on the mountain, and there are fans in various parts of the world.

Natural Whetstones from Kyoto

While many mountains are closed to mining for natural whetstones these days, many others are are still used for sourcing whetstones from all over Japan. One of the most well-known places for natural whetstones is Kyoto (for stones such as Awasedo listed above), which is where many of the natural whetstones we sell in-store come from. Do not discount other regions though - stones can be wonderful for all different kinds of purposes. Be sure to choose what is best for your needs, noting that it may not be from Kyoto.

Kyoto Prefecture also has the Natural Whetstone and Hone Museum (also called the Tennentoishi-kan, or 天然砥石館) that you can visit, which shows the regions' seriousness about the craft.

Picking a Natural Whetstone

Choosing natural whetstones has no real tried and true method. The best and really only way to gauge them is with your own eyes. Of course, talking to experts like us can help you narrow your choices down.

Unlike artificial whetstones which are made to a specific grit number and type, natural whetstones are extracted as they are. This can mean that even the difference of a few centimetres in the mining location can vastly change the quality and expected end result of the whetstone.

Therefore, selecting a natural whetstone that suits you requires a strong understanding of whetstones in general, and the ability to perceive the color and layers of the stone and what they mean. These kinds of stones are truly unique, much like a once-in-a-lifetime encounter.

A Natural Whetstone Proverb

Read this proverb about choosing a natural whetstone - note this has been translated from Japanese and slightly changed to conform to English, the original meaning may be slightly different:

First, the merchant (reliable merchant indicates that quality is also assured)
Second, the hardness (confirm the hardness is suitable for you)
There is no third and fourth (consider your budget)
But fifth is preference (if you like it, you should get it!)

In other words, the above proverb states that you should buy from a reliable store or brand. Next, consult with someone in that store who is knowledgeable about natural whetstones and choose the right whetstone for your usage (hardness is espacially important). About the budget, when it comes to personal preference, investing a bit more in a high-quality stone that you really like is a totally fine!

Natural Whetstone Key Points

Hardness

The faster it absorbs water, the softer it is; the slower it absorbs water, the harder.
The higher the sound pitch when tapped, the harder it is; the lower the sound, the softer.
The heavier it is in your hand, the harder it is, and the lighter it is, the rougher and softer.
The whiter the polishing fluid created while sharpening, the softer it is; and the darker it is, the harder.
Extreme hardness may be difficult to sharpen smoothly, while excessive softness may result in poor sharpening.
If you use a nagura (a stone for preparing and cleaning and maintaining the surface) to smooth the surface, you can sharpen without it causing drag.

How to Judge Quality

No visible defects in color or shape.
Presence of lines or grooves that don't interfere with sharpening.
Even if it is rough, the abrasive grains stand out.
Some are easily broken but have good quality.
When using a nagura, it does not cause drag on the stone, indicating good quality.
Exhibits both hardness and a certain level of viscosity.
Suits the blade and is user-friendly.
Even if expensive, the quality justifies the price.

Reference: 「京都天然砥石の魅力」京都天然砥石組合発行 - “Charm of Kyoto Natural Whetstones” Published by Kyoto Natural Whetstone Association