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||Size in mm
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
#1525 Colorful suita kiita
From the Air Raid Shelter, this suita has lots and lots of
kiita yellow sand and red, purple and black renge lotus flower
elements. A full size bench stone it has been lapped perfectly flat
and is ready to use. I have found it to be a knife or chisel
stone or it can also be used as a pre-finishing stone for
razors. The colorful pattern on the top of the stone looks like a
star cluster or even the Milky Way. This starry night continues
through to the back. There are no areas of identifiable kawa skin
and I cannot recognize which mine the stone came from. I have
honed one knife and the stone was aggressive and fast cutting
and the knife was left with only the finest tooth to the edge, and
one razor where the stone acted like a 2k to 4k synthetic. Used
without slurry it will actively cut steel and in doing so leaves
black steel swarf floating in clear water.
All of the stones in the Air Raid Shelter were from the same era
but I suggest several different mines. Each stone is totally unique
to the other and are not like any processed stones that I have
found in the past 39 years that I have been buying natural
stones from Kyoto. These stones were cut and finished, judging
from the hand cut saw sides, before 1920 and most likely in the
Meiji Era from 1850s to the early 20th century. The colors, shapes
and granular patterns of the hoard are much more organic then the
20th century stones that most of use are familiar with. I have found
and you will feel by testing this stone that the sharpening qualities
are not like the plain monolithic generally colorless stones that are
on the market in this first quarter of the 21st century. These stone
have all been superior in both cutting speed and fineness to the
modern processes stones and the hardness factor is a notch below
the current flood of stones too. These stones are very much
User Friendly as my clients are reporting back to me.
The stone (toishi) has been lapped perfectly 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.
||Size in mm