Kamisori toshi are a special class of stones that are considered fine enough to hone
a shaving razor (kamisori) to the sharpest degree or to be used for honing scalpels,
osteotomes and other medical instruments. It is estimated that only about 10% of the
total tonnage mined in the Kyoto mines in the old days was usable for sharpening
tools or edged blades, the other 90% was waste and left behind. From this 10% the
greater portion of the stone was designated for tools of various types and only a very
small amount, much less than 1% was deemed fine enough for razor honing.

Because this finer grade material was the most valuable category per weight taken
out of the mines, the miners were keen to spot any vein of extra fine stone they came
across and this was set aside for special processing later on. Even odd shaped and
smaller stones were set aside, although not all were necessarily finished up with
perfectly square corners or specific sizes or shapes . In the pre-WW2 era suita and
tomae and various other strata stones of different colors, sizes and sharpening
qualities were offered to barbers as hones by traveling suppliers. The barbers were
expected to choose from an assortment and to pick out through trial and error with
their own kamisori razor the stone he favored.  Some were more rare or expensive
and if stamped were done so by the stone wholesaler.
Over 400 Japanese Natural
Razor Hones in Stock, The
Most Extensive Inventory
Outside of Japan. Just a small
portion shown below.
Just ask for more info.
TheJapanBlade