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Nubatama stone questions

Tue Mar 19, 2013 1:03 pm

Not so long ago I bought a 180x Nubatama from you, excellent stone.
Now - I find myself in need of something in the 5k zone.
I have Choseras and I could buy one of them but Im wondering about the Nubatama 6k stones.
I hone straights - presently I use a 3k Chosera and hop to Botan on a Jnat.
I'd like a bit more refinement before the Botan though.
Now - you have the Ume and Bamboo series.
Do you know which is harder?
By any great chance do you know the abrasive particle size on those stones?
Lastly - given that I'm honing straights - do you have any input on using either the Plum or Bamboo for this?
Im not totally sold on not getting the 5k Chosera, I do love the those stones. But - there's no harm in trying something new is there? Lol.

Thank you


Re: Nubatama stone questions

Tue Mar 19, 2013 1:46 pm

Thank you. I'm glad you are enjoying your '180'.

For your needs, I would not recommend the 5k Chocera. It is significantly softer than the 3k Chocera - in fact the 5k is the softest of the Chocera series of stones so not ideal for use with straights.

I'd go for the 6k Ume. Why? Because you like the formulation of the Choceras and the 6k Ume is similar to the Chocera formulation. Both are Magnesia based formulations in terms of the binding formulation. Both the 6k Ume and 6k Bamboo formulations are much harder than the 5k Chocera - similar to the 3k Chocera, perhaps a slight bit harder.

An 8k stone is equivalent to a 2 micron particle, and a 4k stone is equivalent to a 4 micron particle. So 6k is right inbetween - a 3 micron particle. Particle sizes are pretty consistent with the better quality stones adhering to the Japanese grit rating system.

I'm curious which natural stone you are using or - less likely - if you are using a larger piece of Botan nagura as is done by sword polishers for early polishing stages. If you have an interest I do have some ue-Botan and Koma nagura. The Ue-Botan is somewhat harder and finer than Botan nagura and is found below the Botan nagura.

I'd recommend you reviewing the 6k Ume and 6k Bamboo videos (linked on the CKTG site) and ask me any other questions you might have. I think the 6k Ume will work very well for this application.

Keith, Thanks for asking an excellent question!


Re: Nubatama stone questions

Tue Mar 19, 2013 3:00 pm

Some time ago, I've had the 5k Chosera, and used it very successfully with honing razors. You have to use it splash/go, no soaking. At any rate, the harder Ume seems intriguing, and your answer is what I was looking for; thanks for clearing that up. What is still in question though is particle size. I'm aware of the accepted JIS standard, and I'm sure you are equally aware that not every mfgr follows it to the letter.
My goal, initially was to come up with a stone that has an actual particle size that is around 40% smaller than the Chosera 3k, or perhaps a bit smaller. I did not want to go all the way to the 8k zone though. I find the 40% hop in the Chosera line to be ideal in a progression, the exception is the 1k-3k jump that I deal with. That's why I was looking for a specific, not generalized particle size.
As for Nagura, I use several large Nagura Toishi, as well as a selection of smaller Nagura on a variety of Awase. Some typical, others not so typical.
If you have interesting Nagura, Im interested in them for sure. I'm not familiar with the prefix 'ue' unless you are referring to Mikawa stone that does not have Asano stamps.

One more thing, in general - what exactly is/are the differences between the bamboo and Ume stones?

Re: Nubatama stone questions

Tue Mar 19, 2013 3:48 pm

Yes, I sort of read between the lines that you like the Chocera 'feel', hence my recommendation towards the Ume 6k.

So if we estimate the 3k Chocera to be a 6 micron particle a 40% reduction would be 6*(1-.0.40) = 6 * 0.6 or 3.6 microns or roughly 4 microns or a 4k stone. So if you are considering this sized jump the 4k Ume would be ideal for the same reason - similar formulation to the Chocera stones but firmer.

Unfortunately, as with all of the stone vendors, I can't provide exact particle size or particle size distribution ('spread' of particle sizes) data. I can provide this to you with my CBN and diamond compounds and do have a 4 micron CBN and 4 micron polycrystalline diamond preparation. These can also be used ON a waterstone, as well as on strops, using the deionized water based formulations or water soluble emulsions, giving you some very interesting effects, both abrading the stone and the carbides in the razor, enhancing the edges produced. For natural stones this both increases the slurry density and enhances the rate of slurry refinement, but this is yet another topic.

Several large nagura? I'm intrigued :) It is unusual to find this. You don't also perhaps have an interest in sword polishing too?

I do have both Koma and the ue-Botan nagura. The ue-Botan nagura is a subtype of Botan nagura, nearly indistinguishable from Koma Nagura. It is unrelated to the Asano stamps used by one vendor/supplier for certification (and to control the market IMO). Please send me a PM and we can certainly chat about both my current inventory and any other nagura you might be interested in acquiring.

Bamboo vs Ume. There isn't a clear distinction. It is largely a means of assigning names to stones to avoid confusion. This is especially the case with stones in the 1k range, approximately 9 of them. As a group, the Bamboo tend to be the more expensive stones, with exceptions like the 4k and 6k stones. You can freely intermix the two series. It is best to think of each stone individually and select for your particular purpose - harder stones, softer stones, use with natural stones, etc etc. While traditionally Bamboo would reference a higher quality than Ume or Plum, there are many stones in the Ume series that are certainly not a second tier stone.


Re: Nubatama stone questions

Tue Mar 19, 2013 6:24 pm

From a western POV, paying more for a stone would suggest getting a better stone. From other perspectives though - I suppose choice of characteristics may be what drives the price-point. We all want the best we can afford, and although best is a subjective term, one can't help but wonder why one 6k costs more than another.
So - the Choseras, the 3k is mapped on the grit chart as having 4 um particles. That's why the 5k C with it's 2.8 um particles is a nice fit after the 3k for me.
And - there's the crux of my wonderment about the Ume/Bamboo 6k.
About the Nagura Toishi. They are uncommon for sure - but they are very nice to work with. I do have an interest in sword polishing but only at an informational level. I like to try new/different techniques and stones. Basically - I like to prove to myself whether or not something will or will not work.
A subtype of Botan - not sure that would even be possible since Botan is a Layer, Yae Botan being the only true other version.
Still - I would like to know more; there is no learning without experimentation. I will send a PM after dinner.

Re: Nubatama stone questions

Tue Mar 19, 2013 10:31 pm

Botan is a layer but there is a upper and lower portion to the layer that can be differentiated.

"one can't help but wonder why one 6k costs more than another. "

Well a stone may be better than another but that is one cause for price differentials. Another one is rarity. Something could be rarer raising it's cost but not necessarily more suited to a specific application. Other things affecting cost are things affecting supply and demand. Ease of manufacturing a product, expenses in obtaining an item - postage costs, etc. When pricing natural stones for instance, rarity is certainly an issue, but a perception of the stone's beauty (primarily affected by a Japanese sense of beauty moreso than an American sense of beauty) all effect pricing.

What I try to do is try to understand a customer's needs and try to select what I feel will provide a maximized perceived value for their needs, which are often quite unique. So for instance, I don't provide a standard edge for sharpening a knife, but a more customized solution. It does a butcher little good to put a high grit edge on a soft knife that will be wiped off the first time they swipe it on a ribbed steel.

For the Nubatama stones, it is hard to imagine why the 2k Bamboo stone costs so much for instance. If one is using it on stainless steel, it works but no better than other available alternatives. But on carbon steel, especially in conjunction with natural stones, it is most certainly a truly amazing stone. This is also true of the 3k and 15k stones. I was HIGHLY skeptical of their value until I used them. Having used them it amazes me every time trying to conceive not just how they work but the minds that created such a stone to do what they do. It is hard for me to fathom the generations of knowledge behind such an invention.


Re: Nubatama stone questions

Wed Mar 20, 2013 6:50 am

The layer that Botan is extracted from isn't known to be particularly thick, even if the spotted layer, Yae Botan, is included.
I'm more inclined to find differences in Botan, or any other layer, to be the result of the vein's location when the stone was mined. Stones taken from the original tunnel are markedly different than others. Of course those samples aren't readily available on the market so it's not so easy to experience this. At any rate, for all intents and purposes, all roads lead to Rome and the subtleties become somewhat less important when function is the primary focus.

It's funny, you recommend the Ume 6k and my head says get the Bamboo because its 'better'.
I have always wished for there to be a be a place here in NY where one could go to try stones side-by-side.

Re: Nubatama stone questions

Sat Mar 30, 2013 8:23 pm

OK - bought the Ume 6k even though I wanted the Bamboo. The Ume was in stock, the Bamboo was not, so..s

Anyway - 1st impressions
Nice box, reminds me of some of the Jnat boxes I've had.
Inside- waxy paper covering over the stone - nice touch.
First visuall - stone has a mottled appearance, seems to have a whitish powdery substance on it, but it's not on top of the stone, it's in the stone.
Same on both sides. The top has some wierder mottling though.
Not happy. For 100 bucks I don't think a stone should look like it was soaked in tap water and left to dry poorly.
Anyway -
Lapped it - the stone is in fact hard, definitely harder than the Chosera 5k.
Seems to be a bit thirsty too, but that's not an issue really.
A small chip fell off one corner during the lapping.
Again - not happy. I smoothed it out but this isn't looking good at this point.
It took a while to lap the Ume on a 220x DMT - but it finally trued-up.
First test - a beater blade, a W&B hollow grind razor. The bevel has seen a lot of different stones so it's pretty marked up.
Surprisingly - the stone showed itself to be more than a pretty polisher, it took out a good amount of existing scratches and it polished nicely too.
Second test - W&B 1/2 hollow - following 3k Chosera. I think the Ume has what I'm looking for. There's a good balance of cutting and enough polishing. The Chosera 5k was a good stone but it was softer and did not cut as much. This Ume is still doing a good amount of edge refinement which is what I wanted. I'm convinced this is a good fit for the missing link in the chain. If I had to guess, the 6k Ume is a hair more coarse (grit) than the 5k Chosera. I'm going on memory here - so don't hold me to that.
Under a 4x loupe - the scratch pattern is perfect - no disparate gouges anywhere. The grooves look like perfect wooden soldiers lined up for review.
Now I really want the 6k Bamboo - just to compare.
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