#2122 Hoard Ohira Suita with renge
A super saturated red renge suita from the Ohira mine. A Hoard
stone this is a medium hard stone that is easy to use with hard
steel tools or razors. The base component of this includes yellow
sands, and red radiolarian, a silica element that was formed
by the conglomeration of ancient casts of radiolaria which filtered
to the ocean beds 225 million years ago. The yellow sands percolated
onto the radiolarian as sediment. So you can see that the stone
has a faint yellow cast with red spots.
I honed a Henckles razor after bevel setting on a 1k King stone. On this
suita without slurry, just clear water after setting the bevels edges began
to refine and I could observe this happening within just 20 strokes.
I deem this to be a very fast cutting stone. Next I made a light slurry
with a tomonagura and this speed up the cutting by many times over.
This stone can easily hone up a straight razor, or be used to sharpen
a tool or a knife blade to razor sharp. A rare stone considering that
the Ohira mine was opened in the first half of the 1800's. This stone
was mostly likely mined in the last quarter of the 19th century and
slabbed somewhere between 1880 and 1920.
There is one corner missing on this stone and the price of the
stone is reflected in the value. I also found one very minor bias
seam towards one end outlined in the bottom photo.
The stone (toishi) has been lapped flat and the
corners and edges beveled unless otherwise noted. All of my
stones come with a tested and appropriately sized tomonaguara
slurry stone, and a money back guarantee minus the return shipping.
|All stones are sold with a
money back guarantee
minus the return shipping.
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.
Copyrighted 2017© by Alex Gilmore TheJapanStone
cannot be duplicated without written permission
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|Size in mm