Tomo Nagura Slurry

Slurry 101

Tomo Nagura Slurry 101 

The use of slurry has gained almost mythological status in the straight razor community. Me – personally - I’m not the kind of person that is going to tell anyone that there is only one way to do things, or pretend that I have all the answers. The only truth for anyone will come to him or her through personal experience. 

When finish-honing straight razors on natural Japanese water stones , we often begin this part of the process by raising an abrasive slurry with a small piece of a matching type of finishing stone called a Tomo Nagura. 

Some people want to argue about what a Tomo Nagura is, is not, or what the term actually means. Suffice to say this – a Tomo Nagura is the finest slurry stone used in a Jnat progression. It’s usually similar to the Awasedo but it does not have to be an actual piece of the Awasedo. The Tomo is a tool; it only has to work for you. If you have a small piece of Awase, and it works for you, then it is a Tomo Nagura. 

So – now what?

Assuming we have a razor that’s been honed on some kind of known sharpening system to what might be viewed as being at least 4-8k, we are ready to contemplate our final polish with Tomo Nagura on the Awasedo (aka – finishing stone) – the goal is to refine the edge to our preferred level of sharpness and smoothness.   

What to do? 

The first step, assuming the Tomo has been inspected and proven to not have any sharp edges that might shed hard bits into the slurry, is to make a slurry. 

What is slurry? 

This is the sharpening paste, or mud, that we hone the blade on. With a spritz or two of water on the stone, we rub the working surface of the Tomo against the working surface of the Awasedo. Soon, there is a puddle of stone particles suspended in the water and we call that mud - slurry. 

How do you know if the slurry is ‘right’? 

Well  -if you made slurry then it’s probably right. You might make too much or too little but those things can be corrected fairly easily and honestly – making too much slurry only means having to work on it longer. Making too little slurry means you could possibly undercook the edge but that’s normally not the case. The one thing to note though, is that the consistency of the slurry is important. 

What is too-thick slurry?

If the slurry will not drip off the blade easily, then it’s too thick. Using very thick slurry that’s very muddy might push the edge back too far, making it impossible to recover. It’s best to start with wet slurry, and to keep it wet. Thick muddy Tomo slurry is hardly ever a good thing when honing straight razors. A spritz or two from the water bottle is usually enough to rectify the issue though.   

What is too-thin slurry? 

This situation isn’t really all that problematic. Not having enough slurry and too-thin slurry are similar but they are not the same thing. You can have the right slurry density but not enough of it, or you can have enough slurry that isn’t dense enough. While it’s important to understand the difference, both can lead to an undercooked/unfinished edge. You can always rework the edge though, so this situation isn’t likely to be highly problematic.

How do you know if the slurry is too thin?

This is harder to gauge than knowing when it’s too thick and it’s best learned though practice. Looking at photos of other people’s slurry can give you an idea or two, but it’s possible to be fooled this way. Not every stone’s particles suspend the same way in water, and there are other variables also; coloring, reflections,  bad photos, etc. For me, I find that when the slurry runs off the blade instantly, it’s too thin. I get the best results when the slurry has a certain type of viscosity that gives it some ‘grab’ on the blade. 

Ok – so if the slurry doesn’t flow off the blade it’s too thick, if it does flow off then it’s too thin? WTF?

Pay attention grasshopper…. That’s not what I wrote. 

Slurry density, wetness, or whatever you want to call it, is not going to be gauged by a recipe, formula, scientific investigation or SEM imaging. Getting it right is a learned process that involves a fair bit of trial and error. If you want paint-by-numbers honing go get yourself some crappy lapping film and have at it. Working with natural stones is never going to be like that. 

Patience is key. 

So – back to slurry density; at one end of the scale you have pure water. Watch how it drips off the blade when it’s held perpendicular to the hone. At the other end, imaging how pancake batter would behave here – it won’t budge. What we want, is to be somewhere in between those two points. Where exactly we wind up isn’t terribly uber-critical, but there is a line in the sand where the slurry is just too thick and that’s that.  

My starting slurry usually has a consistency that a tad bit thicker than whole milk, but that’s a poor description because not all milk is created equal. Truthfully though, the exact viscosity isn’t all that important as long as it’s not too thick. If you can imagine the viscosity chart as a line with mud and water at each end, I’d say the good starting points are somewhere in the center 33% portion of that line, and closer to water than mud. 

What is most important is to learn to be consistent here; each time a new session is started, it’s best to start with a relatively close approximation to the previous session’s slurry. This way, when an adjustment is needed, it can be executed with confidence. Without consistency, we are hoping to hit a moving target by shooting blindly into the dark. 

In closing, the best way to learn all or any of this honing jazz is by honing. I’ve had a lot of success by trying to follow the guidelines as best possible, while taking notes and working on being as consistent as possible. Referring to those notes is important also, but sometimes, just writing stuff down helps it stick in my head. 

If you have any questions, just shoot me an email.

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© Keith V Johnson 2014 - 2018