In the previous article in this series your unworthy servant listed some of the tools and accouterments necessary for sharpening Japanese tools using waterstones. In this article we will examine one especially useful stone mentioned previously: the Nagura. I know, it sounds like the name of some smelly, creepy thing that crawled out of a mountain cave in Angmar in Middle Earth, but if you don’t have this little stone, you should get one.
The Nagura Stone
Nagura stones have been used in Japan for millennia, but they are not unique to Japan. For instance, the Coticule stones of Northern Europe have been used with nagura-equivalent stones since before Roman times. And I would not be surprised if the same tradition existed elsewhere too, they are so useful.
There are several varieties of Nagura stones mined in Japan, the two most popular being the grey/black Tsushima stone pictured above and the softer white Mikawa stone pictured below. I use a soft white Mikawa Nagura stone for my straight razor.
The black Tsushima variety is cut from sedimentary stone on the ocean floor near Tsushima in Nagasaki Prefecture, located midway between Japan’s Kyushu island and South Korea. I believe it to be the best for general usage so I will discuss this stone in particular.
Like all Japanese natural stones, Tsushima Black Nagura are mined from sedimentary deposits created by airborne volcanic ash being sifted by distance and wind and filtered by waves and tides by the time they reach the ocean floor. But they have not been subjected to the metamorphic weight and heat that makes harder stones, and are relatively soft and permeable. They also tend to crack in the same plane they were laid down in, especially if subjected to wet/dry and/ or freeze/ thaw cycles, so special measures are necessary to protect them.
The Job of the Nagura Stone
The Nagura stone is typically used to perform five tasks.
1. Cleaning Finishing Stones: Finishing stones become contaminated with pixie dust and grit from rougher stones. A 10,000 grit stone with 1,000 grit particles mixed in is much less than 10,000 grit effective. If you think a stone is contaminated, wash it well with a scrub brush and clean water then work the surface with a clean Nagura stone to loosen and float up the contaminate particles, then wash off the slurry. The stone will be clean.
2. Removing Clogging: Similar to 1 above, the Nagura stone is effective at unclogging dried slurry and metal swarth from the sharpening stone’s surface helping it get back to work sooner.
3. Truing Stone Surfaces: Finishing Stones need to be trued occasionally, usually the corners and edges. Use the Nagura periodically to knock these high spots down. The resulting slurry can be used for your normal sharpening process without it all going to waste. This is wisdom.
4. Reducing Startup Time: Time is money. Waterstones abrade most efficiently when they have a slurry worked up, but it can take time to get decent slurry started on some stones, especially hard ones, and with some blades, especially those with soft jigane. Use the Nagura to quickly develop this necessary slurry saving time and money. If you focus on the corners of the stones, which tend to be high anyway, it will contribute to truing the stone as mentioned in 2 above.
5. Reducing the Average Particle Size in the Slurry: Nagura grit is quite fine. You can add Nagura slurry to a stone (by rubbing the stone to create slurry at corners and edges, BTW) to reduce the average grit size of the slurry making a stone create finer scratches and a better polish. For instance, adding Nagura slurry to a 8,000 grit stone makes it polish more like a 9,000-10,000 grit natural stone.
Using the Nagura Stone
Nagura stones are just as useful when sharpening with synthetic sharpening stones as they are with natural stones. In fact, they may be even more useful with synthetic stones since synthetic stone slurry containing nagura particles more closely approximates the performance of natural stones.
Nagura stones are easy to use. Simply wet the large stone and rub the small stone on its surface. You may need to add additional drops of clean water while doing this. The goal is to wear down the high spots on the large stone while at the same time producing a slurry mixture from both stones to use when sharpening blades.
The key is to pay attention, use your handy dandy stainless steel ruler to identify the high spots, and use the nagura on those areas first. Don’t be a ninny and rub the nagura all over the place willy nilly. Make a plan. Work the plan. Develop good habits and speed will follow.
If the large stone is already perfectly flat, and you need to produce a starting slurry, work the ends and corners of the large stone with the nagura in anticipation of those areas becoming high in the near future. That’s a good boy.
Protecting the Tsushima Nagura Stone
Nagura stones are fragile. To avoid water penetration and cracking, it is wise to use the side of the stone that was in a horizontal plane when it was formed. It is also wisdom to use only one surface of the stone and to coat the stone’s other 5 sides with paint to prevent water infiltration and cracking, and to keep skin oils from penetrating. Traditionally, natural urushi lacquer made from an irritating tree sap has been used for this purpose in Japan, but any high-solids urethane will do the job.
The Nagura stone is a subtle tool. As your skill using natural sharpening stones improves the value of this tool will become apparent.
In the next article in this depraved series about sex, drugs and rock-n-roll, we will discuss ways to maintain sharpening stones. Some people will be miffed. Others will be thrilled. What about you?
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Links to Other Posts in the “Sharpening” Series
- Sharpening Japanese Woodworking Tools Part 1
- Sharpening Part 2 – The Journey
- Sharpening Part 3 – Philosophy
- Sharpening Part 4 – ‘Nando and the Sword Sharpener
- Sharpening Part 5 – The Sharp Edge
- Sharpening Part 6 – The Mystery of Steel
- Sharpening Part 7 – The Alchemy of Hard Steel 鋼
- Sharpening Part 8 – Soft Iron 地金
- Sharpening Part 9 – Hard Steel & Soft Iron 鍛接
- Sharpening Part 10 – The Ura 浦
- Sharpening Part 11 – Supernatural Bevel Angles
- Sharpening Part 12 – Skewampus Blades, Curved Cutting Edges, and Monkeyshines
- Sharpening Part 13 – Nitty Gritty
- Sharpening Part 14 – Natural Sharpening Stones
- Sharpening Part 15 – The Most Important Stone
- Sharpening Part 16 – Pixie Dust
- Sharpening Part 17 – Gear
- Sharpening Part 18 – The Nagura Stone
- Sharpening Part 19 – Maintaining Sharpening Stones
- Sharpening Part 20 – Flattening and Polishing the Ura
- Sharpening Part 21 – The Bulging Bevel
- Sharpening Part 22 – The Double-bevel Blues
- Sharpening Part 23 – Stance & Grip
- Sharpening Part 24 – Sharpening Direction
- Sharpening Part 25 – Short Strokes
- Sharpening Part 26 – The Taming of the Skew
- Sharpening Part 27 – The Entire Face
- Sharpening Part 28 – The Minuscule Burr
- Sharpening Part 29 – An Example
- Sharpening Part 30 – Uradashi & Uraoshi