#398 Ogura mine Heritage asagi/karasu

One of the most unique, beautiful and performance oriented
stones. I told my partner that if stones had a chance, this
one would bleed blood because it looks so very much alive.

An asagi with a karasu pattern that runs throughout the interior of
the stone and which will appear here and there from front to back
in a haphazard way. The front shows a good amount of karasu now
but you can see that as the stone is used the karasu pattern will
change as the stone is worn down and lapped.

The olive green asagi has areas that tend towards the kiita yellow
and then on the back the asagi is more purely green. The second
photo show more clearly the complicated pattern and colors of black
karasu pattern, the greens and shades of blue. All in all
a very complex stone variegated pattern. The sides and ends of
the stone give some indications as to where the karasu pattern
will appear, but only in relation to that immediate area.

There is one serious inclusion that runs in a straight pattern
diagonally through the stone and can easily be seen as holding
rough minerals and with a generally weak looking bond. For this
reason I would suggest that the Ogura be bound in Japanese
mulberry paper and lacquered with several coats.
I will include this service at no extra cost.

You will find that as the stone is used that inclusion will eventually
appear on the top and or back surface, this make take several years
of heavy use. When the inclusion does appear. it fill first be at
the end of the stone, and will only move towards the middle slowly, first one
side and then the other. At 42mm thick this will occur maybe not in our
lifetime. When it does happed it can be picked clean and maintained but
this is something to consider. The price of the stone considers this flaw.

The Ogura was a Kyoto mine in the mountains above Arashiyama and
just west of  the famous mountain Buddhist temple Daikakuji. The mine
is not very well documented but there is reference in a scientific paper
to their stones being used for the honing of surgical scalpels.

To the right is another example from the Ogura mined, an iromono
colored stone that is fully stamped by Hatanaka Company. This example
toishi from Ogura has the distinction of a matching box which has a
label that states that the Ogura mines stones were awarded the
Emperor Showa Inauguration Exposition Silver Coin in 1928.
So the mine was evidently recognized before the second world war.
All stones are sold with a
money back guarantee
minus the return shipping.
Particle Size
9 to
9+++with slurry
Size in mm
Price $4200

Japanese Natural Stones sharpening characteristics.

H or Hardness Scale Explanation.
H Level 6-8 is medium hard and these stones will self slurry under a blade with pressure.
A drop of water placed with a finger tip will sit proud for one minute and then begin to
flatten and seep into the stones surface, within five minutes the drop will be gone.
When using a diamond plate (DP) to lap or make a slurry the action is easy and fast.

H Level 9 is hard and requires concerted pressure and effort upon the blade to self slurry.
A drop of water will sit proud for one half hour and then begin to soak into the surface.
With a DP the stone feels hard and the slurry is thin even with 10 strokes.

H Level 10 stones are the hardest and will not self slurry even under extreme hand
A drop of water will sit proud and round on the surface for one hour or more.
A DP glides over the stone, abrasion happens but very slowly and only with much pressure.

PS or Particle Size Scale Explanation.
PS Level 1-3 (500 to 2,000 grit) for bevel creation are best found in synthetic stones
or with greater difficulty using Arato coarse stones from Japan from areas outside Kyoto
or from individual or successive nagura types stones with appropriate grit levels.
At this grit level steels will brighten but with dull finishes. With laminated blades some
contrasting finishes can be created especially if slurries are utilized.

PS Level 4-6 (2,000 to 4,000) leave medium deep scratches that are easily removed.

PS Level 7-8 (4,000 to 8,000) leave finer scratches that are easy to remove and difficult       
to see with the naked eye but can be seen with a quality 15x loupe. These stones can
a high carbon steel blade looking like polished aluminum to dull chrome.

PS Level 9-10 (8,000 to 25,000) leave the finest scratches at the lowest levels ie. 8k to 12k
of particle size are difficult to see with 15x, under most optical microscopes at 100x are    
easier to see. The scratches at 12k to 25k or natural stones judged to be on par with
these grit levels are difficult to see beyond the 15k level with most optical glass.
The carbon steel or stainless will be bright and polished like a mirror.   

S or Cutting Speed Scale Explanation.
S Level 1-5 at the lowest level have no abrasion power but instead act as burnishing
stones and the upper 5 Level are very slow to abrade tough steel.

S Level 5-7 will cut steel and remove previous scratches easily.

S Level 7-9 will cut steel and remove previous scratches easily and quickly.

S Level 9-10 will excel in the above and at the 10 level will amaze.
Cutting speed can be quantified for personal reference by stroke count.

Japanese Stone Sizes Explanation
Stone sizes in Japan are in millimeters and referred to as "grades" and the sizes stated are
the minimum dimensions which takes into account variables in Length and Width only.
This grade system has its roots at the mine entrance, and is based on a working adults
ability to carry a certain number of grouped and graded by size stones down an average  
mountain trail on his/her back to the valley floor. Working adult refers to a man of average
strength. Women and children also labored but some adjustments of course made.
Grade             Length     Width              Equivalent in inches.
#24 pieces     210mm       78mm             8.26         3.07
#30                205             75                  8.07         2.95
#60                185             70                  7.67         2.75
#80                180             63                  7.08         2.48
#100              160             58                  6.29         2.28
Razor            136              82                  5.35         3.22
Koppa            are by definition bits & pieces and are usually in small sizes

Sharpening Characteristics Explanations.

If all things are equal: a grit rich or silica rich stone will remove a measured amount of steel
faster than a grit poor stone will.
A soft grit rich stone will remove a measured amount of steel faster than a grit poor hard
Like wise if all things are equal: a coarse stone will remove a measured amount of steel
faster than a finer stone will.
In the same vain a slurried stone will remove steel faster than a non slurried stone will.
And again a stone used under running water (that rinses away any loose grit/slurry
particles) will act finer than a stone with standing water, with or without a slurry.

Japanese natural sharpening stones are unique in the world of sharpening for handfuls of
reasons and one of those is their ability to take on different characteristics while in a state of
being used dry, wet, with a slurry or under running water like at your kitchen sink.

One example of this would be that if any one particular high Hard Level Jnat (Japanese
Natural) is used dry and without water their sharpening qualities are diminished and they will
act more like a burnishing stone, but if that same high hardness level stone is used wet it will
act as an abrasive stone. The same goes for coarse stones. Japanese awase-do (aka
awase-to, tennen toishi) really only cut with advanced actions when wet.

And about to slurry or not to slurry. A slurry comprised of loosely bound grit particles
suspended in water, often acting as bundles of bound grit will act coarser and cut faster
strictly depending upon the mechanical action that created the slurry. A #400 diamond plate
will make a coarser acting slurry than a #1200 diamond plate. A nagura or slurry stone cut
from a similar piece of tennen toishi can if harder than the base stones encourage the base
stone to contribute slurry more freely, or if the nagura is softer it will itself provide the
majority of slurry particles. This is the principle for which the Nagura Progression System is
based and this system will only work marginally well with other base synthetic or natural
stones like Coticules, Arkansas and the other slate stones.The Japanese dedicated natural
nagura tend to favor being paired with the natural awasedo found near Kyoto because both
the base and nagura components will encourage the crush of the clays that release the
silica grit of each other.

In all the world the Japanese tennen toishi are unique because of the slurry component and
the way it can be exploited. For centuries the clay binders that comprise the glue that holds
the stones grit in place has been manipulated by sword polishers, carpenters and barbers to
suit their needs and requirements. No other stone will react with such characteristic and
predictable ways as the natural stones that the mountains in and around Kyoto offer.

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cannot be duplicated without written permission