Natural Stones Approximate Grit

Discussion in 'Straight Razors' started by gssixgun, Feb 15, 2020.

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Highest Approximate Grit rating possible in your opinion..

  1. 8k

    0 vote(s)
    0.0%
  2. 10k

    0 vote(s)
    0.0%
  3. 12k

    1 vote(s)
    7.7%
  4. 16k

    3 vote(s)
    23.1%
  5. 20k

    5 vote(s)
    38.5%
  6. 30k

    1 vote(s)
    7.7%
  7. 50k and above

    3 vote(s)
    23.1%
  1. gssixgun

    gssixgun At this point in time...

    Supporting Vendor
    What is the highest grit you think a Natural Stone can be rated at ???

    Absolute highest

    Yes most of us know how hard it actually is to rate them compared to a Synthetic but what do you think ??
     
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  2. joamo

    joamo Well-Known Member

    I'll play at 20K, however, nothing to really base that on. I go to naturals after 1K and don't really give a grit about it. :taunt002:
     
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  3. DaltonGang

    DaltonGang Ol' Itchy Whiskers

    I'll throw in at 20K, possibly a bit more, because the "Arkansas Surgical Black" feels like glass.
     
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  4. Primotenore

    Primotenore missed opera tunity

    Article Team
    No idea...:shocked029:
     
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  5. Jim99

    Jim99 Gold Water Shaver

    I went for 50k and above. “Why?” you ask. I dunno. Glenn, is it possible?
     
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  6. SilverSwarfer

    SilverSwarfer Well-Known Member

    Sinichi Watanabe measures (don’t ask me how) and labels (some of) JNATs he sells. According to his claims, some sport abrasive particles at <1.5u IIRC. Assuming this is true, that gives a theoretic starting size of around JIS >8k.

    See my favorite “grit chart” here:
    https://www.gritomatic.com/pages/grit-chart

    Considering JNAT abrasives are friable, it doesn’t take long to get to 30k+, assuming that particles cleave into halves and continue the geometric progression. I’m no expert and so claim no firm understanding. I’m posting my opinions based on my experience. I would love to hear more from anyone who knows better.

    My vote is for 50k+. I have a purple Shapton 30k as well as a dozen or so JNATs, all but 2 of which are Awasedo or finishing stones. Based on my observations of polishes I’m getting with my stones compared to 16k and 30k synthetics, I’m often seeing scratch patterns much smaller from my JNATs than my synthetics. In some cases I can’t see any scratches.

    It’s not clear whether at some point the stones are starting to burnish and “erase” scratches without traditional abrasion.

    Another point of comparison I have available is from cBN emulsion I use on my strops. Smallest I have is .125u. Synthetic stones and cBN polish much differently at my bench. It’s much more difficult if not impossible for me to get a really clean mirror from JNATs. Instead they polish to a hazy scratchless mirror. My best true mirror polishes come from sandpaper or synthetics or cBN, finished with Autosol or Simichrome buffing. These days I really much prefer the look I’m getting off the naturals. Though it’s a LOT of tedious work with much attention to detail and management of pressure, direction, water, and mud, it’s enjoyable for me. I find myself spending hours working on a nice Kasumi Polish, just to take it to work the next day and effectively ruin my work within the first half hour. Rinse and repeat. Seems crazy but it’s not if I’m having fun and improving my skills polishing over and over!

    At the risk of seeming obnoxious I’m going to repeat what’s already been said again: JNATs just work differently and it’s hard to estimate grit. For me sometimes it seems like it depends on the day. Some stones I know polish great might not always cooperate. Many mysteries remain as far as I’m concerned!
     
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  7. Steve56

    Steve56 Hone Hoarder

    Interesting post with a lot of good discussion points, though maybe tedious for those that are mostly interested in the practical aspects of honing.

    Todd Simpson, the SEM guy at Science of Sharp, says that the jnat slurry does not break down and he has the pictures to prove it. Those of us that hone on jnats know that something happens that makes the slurry act finer with continued honing. Exactly what seems to elude us, but maybe those slurry chunks are rounding off?

    i think that jnats have a much tighter distribution of grit than synths. Synthetics are an engineered distribution of different grits. Jnats, according to most speculation, were formed when a variety of particles were ejected into air, or maybe water. Coarser particles fell out sooner and closer to the ‘event’, finer particles travelled further. I believe this natural action graded the particles much better than synth manufacturing, but this is speculation on my part, though aerosol dynamics are well known.

    The hazy finish is called kasumi as you mention, and it does cover up stuff at normal magnifications.

    I assume that if you're ruining your kasumi in 30 minutes you're speaking of knives. You need some uchigumori fingerstones to clean and restore your kasumi on break! I’ll be glad to send you some, lol, I have a lot of uchigumori.
     
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  8. SilverSwarfer

    SilverSwarfer Well-Known Member

    Yep. I’m taking about my work tools. Knives. Sorry but that’s just my reference point. I most definitely use finger stones because I mostly try to preserve and promote some convexity in my blade roads to promote food release and improve performance. That makes Kasumi very difficult to achieve using bench stones but I still try.

    I have digressed. I thought I would share my thoughts as they flowed. No intent to argue or to profess any particular expertise. Because I have none. Just my thoughts and observations.

    In my eyes it’s not really important the answer to the question but more to gain some insight into others’ thoughts and experiences. Here I had the impression JNAT abrasive was friable but I was wrong. I’m happier to be wrong and learn than to have remained silent and ignorant. I have found considering new perspectives and shifting my approach sometimes improves results. That’s the intended spirit of my response.
     
  9. Steve56

    Steve56 Hone Hoarder

    I hope that I did not come across the wrong way too, that is a problem with the written word. This is a great discussion forum and I am a knife person too! Shigefusa (1), Takeda, many, Tarenjo (1), and many Masahiro, Dojo...
     
  10. DaltonGang

    DaltonGang Ol' Itchy Whiskers

    You guys both did a good job in explaining your thoughts. Now, for those with limited understanding of the Japanese Language, and stones, these conversations might be confusing. Me, I just pick up a little, when you guys get technical, with various JNATS. I'm sort of a JNAT newbie. But, I try to learn.
     
  11. gssixgun

    gssixgun At this point in time...

    Supporting Vendor

    Yeah I don't often listen to people that have less than 5 razors honed under their belt, sorry his study was flawed from the start when he refused the offer of experienced Canadian SR honers to help him...

    The opportunity lost by that decision was a huge loss to our hobby
     
  12. Steve56

    Steve56 Hone Hoarder

    Yep, he’s a world class material scientist and they’re known for shall we say politely, ‘personality’. He did his graduate work at ORNL under a gentleman named Lynn Boatner and I was one of the X-ray safety folks, so I’ve probably met him but it’s been maybe 25 years ago. Small world.

    I think Alex Gilmore gave or loaned him the jnats that he used to examine slurry characteristics.
     
  13. SilverSwarfer

    SilverSwarfer Well-Known Member

    Apologies for the “knife talk” here! Hopefully what follows will be received as a contribution to the conversation, and further explanation of my vote.

    Here’s is an example of finish I’d put at 50k+. The pics are awful but what I’m showing is a scratch free JNAT polish given from Ohira Suita + Uchigumori bench stones. The knife in pic 1 is Shirogami 1 Honyaki Yanagiba forged by Kenichi Shiraki. In English that’s Hitachi White Paper #1 steel, differentially hardened sashimi knife. Pic 2 is a similar knife forged by Yoshikazu Ikeda, in White 2. The Uchigumori is in the background and the Suita is in the foreground of pic 2, and these stones give similar results, broadly speaking. Pic 3 is the Uchigumori shown in its original condition when I received it.

    These stones function differently on different knives. Hard steels, scratches appear to be effectively erased, giving beautiful finishes that capture light in interesting ways. Not a deep “blue” mirror but a hazy crisp, clean reflective surface. Softer steels, scratches start at about 3k and become smaller with progressive work and pressure management.

    It’s fascinating to me and I cannot explain what’s happening to the steel. Maybe it’s not really being abraded in the conventional sense. Maybe the abrasive particles that don’t break down just react with the surface of the steel differently as the surface of the steel becomes more/less smooth with progressive work.

    Further, IME I can’t make this kind of finish without carefully controlling the direction of my strokes. That is, I have to work (nearly) perpendicular to the edge with the Suita and then work parallel to the edge with the Uchigumori. So maybe I’m really just baffling the scratches with a hash pattern so they appear to disappear. If that makes sense, I don’t know! Lol

    Thoughts?

    For razors, I use harder stones but what I see in the loupe reflects the same concepts I’m attempting to explain. Scratches diminish or disappear and the surface captures light in the same way as to resemble the blade roads shown in the pics.
     

    Attached Files:

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  14. Steve56

    Steve56 Hone Hoarder

    First of all those stones are definitely defective and dangerous - please send them to me for proper disposal.

    Uchigumori is not rated to be that fine, usually it’s considered around 3k grit, but it is a polishing stone.

    Are you in Sonoma by any chance? Just curious, you remind me of a gentleman that I used to talk with on another forum a few years back.
     
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  15. SilverSwarfer

    SilverSwarfer Well-Known Member

    Sure thing Steve! Right away... what’s your address??

    the Uchigumori is frustrating to work with on softer knives. I don’t use it for anything but Honyaki, in which application it shines! I know they’re “sword stones,” but truly magic for Honyaki.

    I’m native to WV but cut my teeth in Charlotte, NC. Spent a good chunk of my adult life in CO. Currently I’m hanging my hats in Cincinnati. Never lived in CA but I visited once or twice!
     
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  16. Steve56

    Steve56 Hone Hoarder

    Thank you for your reply sir. You’re not him, lol.

    A cording to So Yamashita’s site, the 4 tenjou layers were uchigumori, nagagumori, sotogumori, and shiro.

    Here’s some eye candy for you, a piece of ‘crow’ tenjou suita bench stone with renge, a Narutaki from Alex Gilmore. Fantastic knife finisher, and it’s it’s fine enough to finish a razor with a bunch of light clear water strokes. I don’t know what layer it’s from, but it’s not hard or soft as things go. The second stone was sold to me out of Japan as uchigumori, but obviously much of it is shiro, packed with red and purple renge. I use this stone after finishing a razor to ‘de-burr’, with a few circles and maybe 3-4 straight strokes. It does boost the HHT a little. I talked with Takeshi about that and he immediately mentioned the be-burring as in what Iwasaki did with the CrOx on the zukka cloth.

    Anyway, fun stuff. They’re both quite impressive face-to-face

    67918A8B-3F6B-4173-B48B-F7BAA72D01DF.jpeg
     
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  17. SilverSwarfer

    SilverSwarfer Well-Known Member

    Beautiful stuff! I have a Suita with similar Renge to the 2nd stone. I never put a razor on it (yet), and I wonder if it would function similarly. Mine is rated at 3.5 (out of 5-5+)on the JNS (Maksim) scale. The stone is wet in this pic but dry, it’s nearly as white as yours. If you were to guess as to your stone’s hardnesses, how would they rate?

    Now, I call my stones what the sellers told me they were. In the world of JNATs I feel like we never really know what are the true origins. And most importantly, you never can tell how useful it might be until you but steel to stone.

    This Suita finishes much finer than the giant pink Renge pictured in my previous post. The bigger stone is also harder, probably just above the “4” rating on Maksim’s scale.

    I have not been honing razors very long so I’m trying to stay focused on what I think is my most appropriate razor stone. That’s a Narutaki (unknown tomae) that I glued to an old Kitayama base, shown in the 2nd pic. I’m happy with the results given my level of experience but I expect to improve. It’s hard to make progress if you keep changing stones/slurries; IME you need to focus on changing 1 thing at a time, much in the same philosophy of the 30 Day Rule threads.

    I’d guess the Narutaki I mention is probably hardness level 5 and finishing around 15-18k, very similar to my Glass 16k, but yet different. This stone cuts slower. It’s not as aggressive. It probably seems contradictory to my claim of 50k+ re: subject of this thread, and it is but this is a different example. It seems to me that the 50k+ is possible with the right steel + stone combination.
    7041B272-2C24-46C0-A004-E4CF7D1EF6AD.jpeg
    51A34BD5-AD35-42F4-8E90-91385EECAFC4.jpeg
     
  18. Keithmax

    Keithmax Breeds Pet Rocks

    I haven’t a clue
     
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  19. SevenEighth

    SevenEighth Well-Known Member

    I'm out of my depth with all this Jnat talk. I have a few stones that do some weird stuff at the high end of finishing. Not sure I could rate them. All I know if that they put an edge on that appears sharper than a fine paste.

    A very dense Charnley Forest
    A very fine vintage coticule
    A vintage yellow lake

    These three I use with oil and the edges go way further than I would expect. It depends on the oil though. Clock oil pushes the edges really far.

    The fourth stone is a strange one. It was advertised as a Yellow Dalmore but so obviously wasn't even before I bought it. It was pretty though and my HAD was in full steam. In appearance it has the veins of a Dalmore blue with a yellow tinge. It came dished and chipped. That stone took so long to lap, I can't tell you. Weeks. Going at it every day. It's a capricious piece of rock. Pretty slow. If you hone just right with water it will maddeningly slowly put the sharpest edge I can get with a natural stone.

    Grit rating? I dunno.
     
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  20. Steve56

    Steve56 Hone Hoarder

    Lol, jnat folks can wax esoteric at times.

    Oh, we like pics of hones!
     
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