I have always struggled with the 1-5++++ hardness scale for razors but have used a 1-10 scale for tool size stones, but in either case the stones for razors in the 1-5 scale have always fallen into the 4+, 5-, 5, 5+ and or course the famous 5+++ ranges. So what is the point of having the numbers 1,2,3 of the scale. I noticed that Takeshi of AFramesTokyo uses the 1-10 scale. Here is my take on the 1-10 scale. Any suggestions would be appreciated, comments and criticisms too.
Alex
Chart
#1 to #2: Soft Aichi/Mikawa or Odori nagura can be 1-2. The softest old mined iro-mono-toishi (literally "colored-things-stones") and light pastel or white early mined stones you can dent with your fingernail can be #1 to #2 in hardness. These soft stones if you can find them, can be used without a tomonagura and will self slurry and they soak up water very quickly even as you are looking at it.
#3 to #5: Medium soft kiita, harder nagura, softer iromono like yellow, red, orange can be 3+ to 5 hardness and cannot be dented with a fingernail. The softest green asagi can be in the 4 to 5 hardness range but these more intense green asagi are not common and they will self slurry under steel sharpening. Water is absorbed easily and you can see it soaking in while you are looking at it.
#6 to #7: Stones like the majority of the duller green asagi, the harder iromono, rich deep gray to black gousa stones can be 6 to 7 hardness. The greatest majority of average tool and knife stones fall into this hardness range. Water is slowly absorbed and a bead of water can stand on the stones in high profile for 5 minutes.
#8 to #9: Stones that are to the touch with a blade are obviously hard and repel water like the hardest asagi, dark gray gousa, many light gray tomae, majority of suita and most mizu-tomae (mizu means water-thus blue). These stones do not self-slurry and do not soak up water easily or quickly and beads of water can stand proudly for up to 20 minutes.
#10: Very hard stones to the hardest, like super hard tomae, super hard suita, dark heavy-dense gray tomae. These types of stones will not volunteer any slurry and even when a diamond plate is used to raise a slurry it is slow and takes noticably more passes to raise what is almost always a white slurry. Level #10 stones are commonly used as a platform base stone for a nagura progression. These level 10 stones do not absorb water easily and a bead of water can remain with a proud profile for an hour or more if left on the stones surface.
Alex
Chart
#1 to #2: Soft Aichi/Mikawa or Odori nagura can be 1-2. The softest old mined iro-mono-toishi (literally "colored-things-stones") and light pastel or white early mined stones you can dent with your fingernail can be #1 to #2 in hardness. These soft stones if you can find them, can be used without a tomonagura and will self slurry and they soak up water very quickly even as you are looking at it.
#3 to #5: Medium soft kiita, harder nagura, softer iromono like yellow, red, orange can be 3+ to 5 hardness and cannot be dented with a fingernail. The softest green asagi can be in the 4 to 5 hardness range but these more intense green asagi are not common and they will self slurry under steel sharpening. Water is absorbed easily and you can see it soaking in while you are looking at it.
#6 to #7: Stones like the majority of the duller green asagi, the harder iromono, rich deep gray to black gousa stones can be 6 to 7 hardness. The greatest majority of average tool and knife stones fall into this hardness range. Water is slowly absorbed and a bead of water can stand on the stones in high profile for 5 minutes.
#8 to #9: Stones that are to the touch with a blade are obviously hard and repel water like the hardest asagi, dark gray gousa, many light gray tomae, majority of suita and most mizu-tomae (mizu means water-thus blue). These stones do not self-slurry and do not soak up water easily or quickly and beads of water can stand proudly for up to 20 minutes.
#10: Very hard stones to the hardest, like super hard tomae, super hard suita, dark heavy-dense gray tomae. These types of stones will not volunteer any slurry and even when a diamond plate is used to raise a slurry it is slow and takes noticably more passes to raise what is almost always a white slurry. Level #10 stones are commonly used as a platform base stone for a nagura progression. These level 10 stones do not absorb water easily and a bead of water can remain with a proud profile for an hour or more if left on the stones surface.
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