JNAT Scale

Grading Shiageto/Awasedo JNATs can be quite subjective! That is why we tried to come up with a comprehensive grading scale, based on objective criteria, that can be used to quantify them accurately.


Main Grades

These are the primary factors that determine how a stone will act during use. While "Hardness" and "Fineness" somewhat correlate, they can vary enough to warrant assigning them separately.


Hardness

The hardness of each stone is determined by performing a water displacement (specific gravity) test using a specially designed rig. This method is the most accurate one to determine the actual hardness level of a stone.

  • Level 5+/5 – Very Hard (>2.70 g/cm3)

    Stones in this range will be able to produce very keen edges that offer a low amount of comfort. Finished with this type of stone, edges will exhibit the lowest amount of micro-convexity at the apex.

  • Level 5/5 – Hard (2.60 g/cm3 - 2.70 g/cm3)

    Stones in this range will be able to produce highly keen edges that offer a reasonable amount of comfort. Finished with this type of stone, edges will exhibit an adequate amount of micro-convexity at the apex.

  • Level 4.5/5 – Medium/Hard (2.50 g/cm3 - 2.60 g/cm3)

    Stones in this range will be able to produce fairly keen edges that offer good amount of comfort. Finished with this type of stone, edges will exhibit a significant amount of micro-convexity at the apex.

  • Level 4/5 – Medium (2.35 g/cm3 - 2.50 g/cm3)

    Stones in this range will be able to produce moderately keen edges that offer a high amount of comfort. Finished with this type of stone, edges will exhibit the highest amount of micro-convexity at the apex.

  • Level 3.5/5 – Soft/Medium (2.25 g/cm3 - 2.35 g/cm3)

    Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.

  • Level 3/5 – Soft (2.10 g/cm3 - 2.25 g/cm3)

    Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.

    • Level 2/5 – Very Soft (2.00 g/cm3 - 2.10 g/cm3)

      Stones in this range are too soft and will dish excessively. They are therefore completely unusable for razor honing.

    • Level 1/5 – Extremely Soft (<2.00 g/cm3)

      Stones in this range are too soft and will dish excessively. They are therefore completely unusable for razor honing.


    Note: Although harder stones yield keen edges more easily, that doesn't mean softer stones can't. Their surfaces simply take longer to exhaust and therefore burnish. It's worth noting though that harder stones are more challenging to hone on.


    Fineness:

    The fineness of each stone is determined by analyzing the scratch pattern on the DOVO silver steel (115CrV3 @ ~61 HRC) straight razor at 150x to 200x magnification after performing the cutting power test described below.

    • Level 5+/5 – Very Fine (>12k JIS)

      Stones in this range will achieve a very finely blended and perfectly uniform scratch pattern. When examined under magnification, there will be no visible individual striations and/or parasitic scratches.

    • Level 5/5 – Fine (10k - 12k JIS)

      Stones in this range will achieve a finely blended and practically uniform scratch pattern. When examined under magnification, there will be faintly visible individual striations and/or parasitic scratches.

    • Level 4.5/5 – Medium/Fine (9k - 10k JIS)

      Stones in this range will achieve a thoroughly blended and predominantly uniform scratch pattern. When examined under magnification, there will be slightly visible individual striations and/or parasitic scratches.
    • Level 4/5 – Medium (7k - 9k JIS)

      Stones in this range will achieve a moderately blended and sufficiently uniform scratch pattern. When examined under magnification, there will be clearly visible individual striations and/or parasitic scratches.

    • Level 3.5/5 – Coarse/Medium (6k - 7k JIS)

      Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.

    • Level 3/5 – Coarse (4k - 6k JIS)

      Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.

    • Level 2/5 – Very Coarse (2k - 4k JIS)

      Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.

      • Level 1/5 – Extremely Coarse (<2k JIS)

        Stones in this range are not recommended for the finishing stage but can be used for the pre-finishing stages.


      Note: As the fineness of a stone increases, the apex becomes more refined and the microscopic teeth (feathers) become less jagged. This results in a smoother feeling on the skin during shaving and reduces post-shave irritation.


      Sub Grades

      These are assigned in relation to the "Main Grades." A coarse stone will, by default, remove metal faster than a fine one and a soft stone will, by default, generate more resistance and provide a different type of feedback than a hard one.


      Cutting Power

      The cutting power of each stone is determined by testing how the stone performs with its own slurry. This process involves a #1200 Atoma plate, to generate slurry, and a DOVO silver steel (115CrV3 @ ~61 HRC) straight razor.

      • Level 3+/3 – Very Fast

        Stones in this range will exhibit a very fast change in slurry color during honing. It takes around 5 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.
      • Level 3/3 – Fast

        Stones in this range will exhibit a fast change in slurry color during honing. It takes around 10 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.

      • Level 2.5/3 – Standard/Fast

        Stones in this range will exhibit a prompt change in slurry color during honing. It takes around 15 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.

      • Level 2/3 – Standard

        Stones in this range will exhibit a moderate change in slurry color during honing. It takes around 20 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.

      • Level 1.5/3 – Slow/Standard

        Stones in this range will exhibit an adequate change in slurry color during honing. It takes around 30 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.

      • Level 1/3 – Slow

        Stones in this range will exhibit a slow change in slurry color during honing. It takes around 40 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.


      Note: The harder a razor is, the higher the stroke count will be for swarf to start building on the stone. However, the cutting power does not affect the end result in any way. It simply dictates how much time you need to spend on the stone.


      Tactile Feeling

      The tactile feeling of each stone is determined by evaluating the resistance felt against the bevel of the DOVO silver steel (115CrV3 @ ~61 HRC) straight razor and the feedback it provides while performing the cutting power test described above.

      • Level 3+/3 – Very Smooth

        Stones in this range will provide a very smooth feedback without any tactile sensation felt during use. The surface of the stone will offer no resistance to the blade as it moves over it.
      • Level 3/3 – Smooth

        Stones in this range will provide a smooth feedback with a faint tactile sensation felt during use. The surface of the stone will offer almost no resistance to the blade as it moves over it.

      • Level 2.5/3 – Standard/Smooth

        Stones in this range will provide a crisp feedback with a slight tactile sensation felt during use. The surface of the stone will offer slight resistance to the blade as it moves over it.

      • Level 2/3 – Standard

        Stones in this range will provide a solid feedback with a moderate tactile sensation felt during use. The surface of the stone will offer some resistance to the blade as it moves over it.

      • Level 1.5/3 – Heavy/Standard

        Stones in this range will provide a firm feedback with a distinct tactile sensation felt during use. The surface of the stone will offer noticeable resistance to the blade as it moves over it.

      • Level 1/3 – Heavy

        Stones in this range will provide a heavy feedback with a strong tactile sensation felt during use. The surface of the stone will offer significant resistance to the blade as it moves over it.


      Note: The harder a razor is, the less resistance the stone will generate during use due to reduced friction. However, the tactile feeling does not affect the end result in any way. It simply determines the type of feedback a stone will provide.