Is there a another Jnat lurking on the bottom of my Jnat?

[BDF]

Probably a dumb question but anyway, my Jnat (I only have one) bottom looks like it could be turned into a honing surface. The bottom is more sandy colored than the top, which is 90% gray with blonde edges. It would require a significant amount of material removal, something between 1/8th inch and 3/16 inch. Not having a clue about how this is normally done, I would go about it with a diamond cup wheel, getting as close to flat as possible and then finishing flattening it with diamond honing plate(s).

Is there a reason(s) why this cannot or should not be done? Is there an accepted way of removing significant stock from a stone rather than using hand held power tools and 'being careful'? As long as I keep the stone from getting hot and isolate it with materials that will not cause any shock to the stone while grinding it (soft materials as opposed to sitting it on a concrete block for example), is there any downside to trying this? I have a background as a toolmaker so I do realize the precision required for the rough grinding... my plan would be to treat the diamond grinding in a similar way to scraping iron which is taking down the high spots until the remaining surface is flat w/in a reasonable range of say, 1/32" or less and then using a diamond plate such as an Atoma to do the final flattening. Unless of course there is an accepted method of doing this more directly.

My motivation here is that the bottom of the stone appears to be quite different than the top, the honing surface.... and it might provide a different Jnat to try out. ???

 

[Steve56]

That kiita layer is really thin. I think that you’d be through most of it by the time that you got a usable surface, but it’s do-able I think. You will lose that spot of shiny black skin on the back, that’s the Nakayama provenance - that shiny black kawa was the only unique marker for Nakayama according to Alex Gilmore.

 

[BDF]

So if I am following you Steve, you are saying it will devalue the stone if I cut that black speckling off the back? Interesting- as you know, I know absolutely nothing about Jnats so I simply cannot put a value on any stone.

 

[Steve56]

It will not devalue a gray stone as much as a fancy looking one. If you lap it, keep the edges chamfered as you go, sharp corners like to chip out.

 

[SliceOfLife]

Had a prefinisher for years. One day I lapped the backside and it was a darn good finisher. Could work out.

 

[BDF]

So I grabbed a coarse flattening stone and went at the other side of my Jnat hoping to free perhaps the best Japanese razor honing known in the history of edges. I certainly did get a different Jnat.... The face, the original honing surface, is mostly medium gray, quite hard and has a very slight sheen to it when dry. As I am pretty ignorant about Jnats, I say it is quite hard because it really resists producing a slurry with an Atoma 1200 diamond plate. The reverse face however is yellowish and by comparison very soft. Two or three passes with the Atoma and not only is there a slurry, it is quite thick sorta' like yellow peanut butter.

I certainly did not do a complete job of lapping the reverse face but I have a large enough flat plane to do a test hone or two. I suspect this face is soft enough to self- slurry and may be too coarse to be an effective razor hone. But another hit with cashew lacquer and the reverse can go back to being a place to sit on the bench while honing on the right or 'good' side.

 

[H Brad Boonshaft]

Natural stones can be very different from one side to the other. Go to a stone yard where Granite, Marble and other stones slabs are store in flitches as they were cut from the stone block. You will see that all the slabs are very different from one side to the other.

Over the thousands/millions of years that nature took to create the stone all manner of debris landed in the mud and decomposed to created color and texture that became stone.

So, yes, any natural stone can be very different on the back side. Hone a razor from a 1k bevel set with some 400-600 diamond slurry to test the aggressiveness and finishing ability.

 

[BDF]

Bearing in mind that this is my first and so far, only Jnat.... I find the gray face very hard and fine. I say that because it is tough to raise a slurry with a 1200 grit diamond plate. And the slurry has no 'feel' to it at all, feels like water. The reverse face of the stone slurries very quickly and leaves a slurry like mud. It seems a LOT softer than the front face. It also gives quite a bit more feedback, both in feel as well as sound in use than the front face, which has very little feedback, at least that is how it seems to me.

I honed one razor on the back side of the Jnat and it yielded what seems like, using tree- topping as a sharpness test, the edge is similar or the same as the front face. But take all of this with a gigantic grain of salt as I am about 2 months into my first and only Jnat so it is not as though I have a wide range of Jnat experience to draw on.....

 

[H Brad Boonshaft]

Jnat base stone and slurry can be very subtle or aggressive and technique dependent.

You have compounded your Jnat learning curve. Slurry itself is a deep hole, diamond slurry from 300-1200 will perform differently, again depending on technique.

When you get to Nagura you will discover a cornucopia of grit ranges. My advice is to stop comparing to synthetic stones, (feel, feedback, softer, harder) and make quantitative comparisons, like shave test to calibrate each side of your stone, and experiment.

A year from now it will be a very different stone, not really but may perform very differently.