Thread: Japanese Natural Waterstones: What's in the name?

JimR has a very interesting blog entry here on Japanese natural stones.

Originally Posted by Kingfish

Maybe no book or standardization will ever be made to satisfy a very small minority of craftsman(including razor sharpeners). Certainly it would not do justice. Some things just take a long time with no instant answers available.

Kind of off topic but ..... there is a big book on the Belgian Coticule .....; so I hear .... but it hasn't been translated into English.

Wouldn't do me much good then. I took a semester of German in college about 20 years ago...only remember a couple phrases now. I am just starting to really play with the coti and am liking it. Seems to really give a smooth shave. May not leave the sharpest edge, but it's smoooooth. That's just a couple blades though.

Originally Posted by JimmyHAD

JimR has a very interesting blog entry here on Japanese natural stones.

I will agree with Jim !! Very good article !
But not for everything

I get some super edges from Charnley and Thuris same as Jnats.
But for knifes or sward polish Jnats just stands out of all Natural stones out there !!
I can not bring same finish to my knifes or Tamahagene steel on Charnley, Thuri or coticule or other stone out there.
So i guess they are very very unique stones ! And thats why they are so expensive, because sward polishers all over the world count them as best polishing stones out there !

But for razors and sharpness Jim is totally right !

Originally Posted by JimR

There is no "most used" system, everyone who puts numbers (or letters) on a stone uses their own. Even if they happen to have the same numbers (for example, 1-5) there is no standard way to decide those numbers. They might as well just use "kind of expensive-really expensive".

Yep
Those systems is just for individual seller, most for them self then for costumers or for costumers that will buy more stones from same seller, so they know they will buy harder or softer stone then they bought befor.

One seller can have lv 2 stone as soft as other sellers lv 5
So dont count on those systems ! Tell seller instead what you will use it for and what you are used too now.

But there are lv 2 stones that is more expensive then Lv 5+ so it is not price systems at all !

As for hardness of jnats there is a true way to get scientifically correct info about.
It is some kind of sclerometer or scleroscope

Whether scratch sclerometer ( AKA Turner-sclerometer), rebound (Leeb) or Brinnel type...

Sclerometer, R. Fuess, Steglitz, Berlin

this can give exact and reproducible measurments of hardness

As far as i know one of well known jnat merchant in Tokyo use some kind of sclerometer (or hardness meter) on the stone he sells
because all of the stones he sell have characteristic mark of indentor.

It seems to me that hardness meters for resin/rubber (Shore type) can be used for jnats hardness characterisation.

here it is examples of Shore durometers:
http://www.instron.ru/wa/library/str....aspx?sdoc=529


As for hardness rating like Lv1, Lv2... or so called HGAL system
with hardness rate in the range from 1 to 5
it seems to me it is non-nonsence system
it is a kind of rating system
based on comparison with reference sample
like the Mohs scale of hardness that is widely accepted in mineralogical practice
( http://www.diamond-jewelry-pedia.com/mohs-scale.html )

So the question is What are that reference samples to compare with?
we know them for the Mohs scale
but I don't know which are they for jnats...

BTW we can try to collect the database of hardness of well known jnats
with well known properties
using some standard hardness measurment method like Shore
and try to make our own scientifically based system of jnats hardness estimation.

Some more info on methods of hardness testing:
http://www7.taosnet.com/ebear/metal/hardness.html
http://www.substech.com/dokuwiki/dok...s_test_methods


We can even use some home grown Brinell-like technique like applying the hard ball with known diameter
to the surface of the stone with know pressure (force) for known time
and measuring the diameter of the round indent on the surface
using portable microscope like PEAK WIDE STAND or Dino-Lite Pro
( http://www.instron.us/wa/application...s/brinell.aspx
http://www.gordonengland.co.uk/hardness/brinell.htm )

So all we need for this are simple loading device (weight with guide ), the indentor ball and the microscope with appropriate scale.

Hi Nicolay,
Lots of good stuff there, but I think many of us using the term hardness as applied to the Jnats might be misplaced. Given that most Jnats are related fairly close geological markers like Moh's scale could be misleading. One could easily misake friability and fracture for scatch type tests IMHO.

For those not familiar with mineralogical ratings of hardness, by definition the active part of a coticule, the garnet is considerably much harder than the quartz silicate abrasive in a novaculite type like an Arkie(sounds silly but true), the abrasive particles in the Jnat would be inbetween the two. In other words we would have to differentiate which property we are trying to classify. I do believe this confusion is one of the main reasons that there is a resistance to scientifically rate Jnats that way.

I propose that they could be rated by friability differences and even then there individualist nature could make that classification less than meaningful or even worse misleading and superficial to their singular nature and quality owing to the fact they are by definition rocks (not minerals) with many factors that produce performance and as individual as the honers who use them. Not saying that an agreed way to classify them could not be made up and baptized but it would be an oversimplification at best.