JNAT Scale
Grading JNAT whetstones can be a pretty subjective matter! We tried to come up with a comprehensive grading scale based upon objective criteria that can be used to quantify razor stones accurately without relying solely on how a stone feels.
Hardness
We do not stock stones below level 4 hardness because our experience has shown that stones below this threshold lack the requisite level of density for optimal razor honing performance.
- Level 4/5 – Medium: 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 micro-convexity at the apex.
- Level 4.5/5 – Medium/Hard: 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 micro-convexity at the apex.
- Level 5/5 – Hard: 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 micro-convexity at the apex.
- Level 5+/5 – Very Hard: Stones in this range will be able to produce extremely keen edges that offer a low amount of comfort. Finished with this type of stone, edges will exhibit the lowest amount micro-convexity at the apex.
The density of each stone is determined by performing a water displacement test to find . These methods are the most accurate ways to determine the actual hardness level of a stone.
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.
Abrasiveness
We do not stock stones below level 4 abrasiveness because our experience has shown that stones below this threshold lack the requisite level of cutting power to effectively hone razors.
- Level 4/5 – Medium: Stones in this range will exhibit a moderate 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.
- Level 4.5/5 – Medium/Fast: Stones in this range will exhibit prompt 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 5/5 – Fast: Stones in this range will exhibit a rapid 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 5+/5 – Very Fast: Stones in this range will exhibit an immediate change in slurry color during honing. It takes less than 5 half strokes, performed with light pressure and a medium slurry, for swarf to start building up on the stone.
The cutting power of each stone is determined after 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.
NOTES: The harder a razor is, the higher the stroke count will be for swarf to start building on the stone. However, abrasiveness does not affect the end result in any way; it simply dictates how much time you need to spend on the stone.
Fineness:
We do not stock stones below level 4 fineness because our experience has shown that stones below this threshold lack the requisite level of refinement needed to put a superior shaving edge on a razor.
- Level 4/5 – Medium: Stones in this range will achieve a reasonably blended and adequately uniform scratch pattern. When examined under magnification, there will be clearly visible individual striations and/or parasitic scratches.
- Level 4.5/5 – Medium/Fine: Stones in this range will achieve a largely blended and mostly uniform scratch pattern. When examined under magnification, there will be moderately visible individual striations and/or parasitic scratches.
- Level 5/5 – Fine: Stones in this range will achieve a virtually blended and nearly uniform scratch pattern. When examined under magnification, there will be faintly visible individual striations and/or parasitic scratches.
- Level 5+/5 – Very Fine: Stones in this range will achieve a completely blended and perfectly uniform scratch pattern. When examined under magnification, there will be no visible individual striations and/or parasitic scratches.
The fineness of each stone is determined by analyzing the scratch pattern on the DOVO silver steel (115CrV3 @ ~61 HRC) straight razor after performing the cutting power testing outlined above. This is done using a 220x Dino-Lite microscope.
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.