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JNAT review - Karasu rock

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riverie

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Thank you D. Very informative as always.
 

maxim

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Thanks Harald ! Another good review that stone look amazing :)
 

Darkhoek

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Thanks Harald ! Another good review that stone look amazing :)
It is a great stone. But like most of my really good finishers, it is very thin, which is probably the only reason I can afford it :) This is one of those stones I really would like in full size, but wife says I still need my car, so for now it is out of reach :(

Thanks everyone for your comments and interest in my blog.

DarkHOEk
 

SpikeC

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Just replace your car with a moto of some sort and yer golden!
 

DrNaka

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Nice review of your Karasu Harald-san.

Two comments about your review:

1. There is rumor that some sellers just stamp Nakayama and there are fake Nakayama stones in the market.

But I have another view of it.
About 10 years ago carpenters of kezukro-kai found that hard and fine Nakayama are best to their planes wich they use for competition.
Here some pictures of the competition:





Many carpenters bought Nakayama stones which give a keen edge on their planes.

Price of Nakayama stones went up and the quality of the remained stones went down.
Only the hype that Nakayama stones are good remained.

I think the Nakayama stones which are sold now are real Nakayama stones but just left over of the very good stones.
I think you could find a very good Nakayama because it was thin.
I write about thin stones in the next comment.

2. About thin stones
Many Jnats stone collectors with experience in Japan are looking for thin stones.
Not because thinner stones are cheaper.
The chance you find a gem stone is bigger.
The logic is that smaller sediment will take longer time to grow.
If you know about terminal velocity you will know that settling velocity goes down when the particle is smaller.
So the layer of very fine stones are thinner.
 

Darkhoek

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Nice review of your Karasu Harald-san.

Two comments about your review:

1. There is rumor that some sellers just stamp Nakayama and there are fake Nakayama stones in the market.

But I have another view of it.
About 10 years ago carpenters of kezukro-kai found that hard and fine Nakayama are best to their planes wich they use for competition.
Here some pictures of the competition:





Many carpenters bought Nakayama stones which give a keen edge on their planes.

Price of Nakayama stones went up and the quality of the remained stones went down.
Only the hype that Nakayama stones are good remained.

I think the Nakayama stones which are sold now are real Nakayama stones but just left over of the very good stones.
I think you could find a very good Nakayama because it was thin.
I write about thin stones in the next comment.

2. About thin stones
Many Jnats stone collectors with experience in Japan are looking for thin stones.
Not because thinner stones are cheaper.
The chance you find a gem stone is bigger.
The logic is that smaller sediment will take longer time to grow.
If you know about terminal velocity you will know that settling velocity goes down when the particle is smaller.
So the layer of very fine stones are thinner.
DrNaka,

Now, THIS is the kind of information I am looking for! It makes sense what you say. This tells me what to look for and where to look for it. The Karasu in question is not the finest, yet it takes my edges to unbelievable sharpness. My rather uneducated theory behind this is that because the karasu is so pronounced the grit range of the stone might have widened. The karasu or mica grit might be around #3-4000 and the grey, green,yellowish material inbetween might be #10-20000 as it breaks down. I suspect this to be one of the reasons why this stone performs so well and produce super sharp edges with such high wear resistance. As I said this is wonky logic from my rather uneducated mind in this field. :confused:

The Oohira kiita or shiro suita in one of my earlier posts http://*****************.com/2010/11/ohira-kiita-suita.html has some of the same issues. Quite thin but exceptionally clean and fine grit. This Oohira is one of my other true gemstones. The board of this stone is mustard yellow, but as I wear it down it lightens up to a white/pink/lightblue-ish colour. The stone is probably quite old and I have read that old suita stones can have a rather thick dark yellow oxidised layer on the board that will wear away over time. This looks to be right for this one. Again I would appreciate any information you might extract from the pictures regarding the true heritage of the stones in my blog. They are presented as the same kind of stone they were purchased, as I do not have the knowledge and experience to identify stones exactly by their colour, appearance, skin and performance. Hopefully I will be better at it in the future, but this presupposes that the information I base my education on is fairly correct. If you find the time and interest I would appreciate any comments to my blog if you toishi experts out there have information on the rocks reviewed in there.

Thanks again, all, for your interest. :)

DarkHOEk
 

mainaman

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The increased wear resistance of the edge, comes from shock hardening of the steel when sharpening. According to some sources a study has been done in Japan showing increased HRC at the edge of a knife sharpened with natural stones. How truthful that is I do not know, hope someone more knowledgeable will chime in, but I have seen increased edge retention from my knives too.
 

DrNaka

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Harald-san

I can estimate price of a Jnats if I know the store which sell it, the mine and the picture of the stone.
But I cannot estimate the quality of the stone with surface picture.

I see at swarf/mud ratio and the finish on the blade to estimate the quality of the stone.
If I see video of maxim I hear the sound too.

Do not be fooled by the appearance of the stone.

swarf/mud ratio , finish on the blade, sounds are the key.
 
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