Guesses about jnat vs coticule

[kohalajohn]

The received wisdom about finishing seems to be that it's done differently on jnats vs coticules. I'm trying to guess at why.

My experience with my coti is that to finish, it's best done under running water with no slurry.

But for jnats, its different. To finish, keep some slurry, but keep doing laps and wear down the slurry.

From the electron photos I have seen on Science of Sharp, the silica particles in jnats don't fragment into small pieces. But despite this, jnats do "behave" over the lapping period as if they are getting finer. And we can actually see the groove lines getting shallower.

So it must be that the particle's sharp edges are becoming dulled with use. That makes the jnat particle cut as if it has become a finer particle. The particle is the same size, but the sharp edges sticking out from it are becoming dulled and it is no longer cutting as deep into metal.

I wonder. Are the hard garnets in cotis so hard that they just don't become dulled with use? They keep cutting deep grooves, so eventually you just have to wash the slurrry away and just lap on the hard coti surface, like the slippery surface of a black ark?

 

[Steve56]

I think that’s a pretty good guess for many cotis and jnats John, but being natural stones, you will find exceptions in both categories. I definitely have jnats that make a better edge on clear water, and some folks like a little slurry on their particular coticule, though that seems more uncommon. And maybe that’s unsurprising, coticules are reportedly not that fine (and the scratch pattern under my loupe is anything but fine) but the shape of the abrasive/scratches make them shave better than you’d expect from a synth of similar grit.

 

[rideon66]

Also with Coticules it has more to do with the shape of the particules and how they shape the edge differently. The geometrical shape of these garnets is a dodecahedron. There are twelve surfaces with obtuse angles. The garnets have a diameter of 5 to 15 microns and penetrate 1 to 3 microns into the metal to be sharpened. This ideal geometric shape (obtuse angles polish the metal) and the large numbers of these garnets ensure that the blade is sharpened both very quickly and extremely finely. These also don't break down. So fast cutting and not breaking down in general is why most finish on clean water, but that isn't always the case with ever Coticule. I have some you need to finish on faint slurry. My understanding of JNATS is that the slurry particles have a friability so it does get finer and the cutting action slows. Again why many are able to finish on slurry, but not the rule either as Steve has stated. I forget off hand, but there was at least one layer of coticule that needed slurry to get a good finish.

 

[lightfoot]

If I use a Coticule as the final stone I just hone on water from my spray bottle rather than running water without slurry. To take it a step further I’ll add a thin film of shave lather and hone with the lightest strokes I’m capable of.

 

[stone and strop]

I think its really stone dependent, even within the same species.
There are exceptions like Arks that are oil or water only. Very few if any would slurry an Ark.

 

[Tomo]

I finish Coticules on oil and Jnats on soap. No slurry for the final stages on either.

 

[Slash McCoy]

The received wisdom about finishing seems to be that it's done differently on jnats vs coticules. I'm trying to guess at why.

My experience with my coti is that to finish, it's best done under running water with no slurry.

But for jnats, its different. To finish, keep some slurry, but keep doing laps and wear down the slurry.

From the electron photos I have seen on Science of Sharp, the silica particles in jnats don't fragment into small pieces. But despite this, jnats do "behave" over the lapping period as if they are getting finer. And we can actually see the groove lines getting shallower.

So it must be that the particle's sharp edges are becoming dulled with use. That makes the jnat particle cut as if it has become a finer particle. The particle is the same size, but the sharp edges sticking out from it are becoming dulled and it is no longer cutting as deep into metal.

I wonder. Are the hard garnets in cotis so hard that they just don't become dulled with use? They keep cutting deep grooves, so eventually you just have to wash the slurrry away and just lap on the hard coti surface, like the slippery surface of a black ark?

GENERALLY, yes, coticule finish should be under running water, but you may encounter exceptions. Try it that way, then try variations such as lather, soap, oil, etc. Leave the oil for last. Sometimes it takes a bit of work to "un-oil" a coticule. Dish soap clears easily, as does most shave lather. And yeah, the garnets are almost indestructible. They don't break down. The only real variable that changes during honing is how many of them are rolling around on top of the stone, and how much buffering is provided by the honing fluid. And of course things like your pressure and stroke technique. If you have a combo stone, don't forget to try the BBW side.

Jnats are all over the board. Some finish nicely with clear water. Some don't. Most hardcore Jnat guys like to keep working the slurry and breaking it down, and thinning with water for the finish. Different stones and different slurry stones behave differently.

 

[PaulMallorca]

Some of my coticule become prety polished on water only. They slow down a great deal and with enough strokes edge surface finish changes. Under the scope is easy to see how the particles are relativelly loosely held in place, so intuitively I have the theory that once most of the surface garnets get worn and dislodged on water only, the other particles composing the stone have a chance to show what they can do. Would explain hybrids and why the BBW can occasionally be a great finisher even if the garnets tend to be bigger.
Is like a two speed stone, fast when garners can do most of the work, fine when the quartz and what else is in there gets the over hand.

As the texture of coticules changes a lot, so could do their ability to shred or retain garnets.
My soft coticules need running water and don't seem to develop a polished surface.
The hard ones go shiny and don't autoslurry, giving me overall better finishes. Work with a rubbing stone reveals a new fresh garnet loaded surface. Fast but not as capable as a finisher.

But is just a theory...

 

[SliceOfLife]

I put coticule slurry under a scope and the good ones garnets are nowhere near what the commonly believed coti garnet sizes are.

My COARSEST coticules (ones I wouldn't finish on... two vintage 10" stones that cut like coarse sandpaper) had ~12-20 micron particles.

Ones that I considered below avg (a modern LNV) had 5-8micron particles.

Average to Avg+ (Most vintages that don't feel ultra-glassy and the majority of "good" moderns I've owned... a good example would be a fast LV) 1-3 micron particles.

Top notch finishing coticules you couldn't tell the slurry from a 13k+ synth or a Thuri or finishing Jnat. All sub 1 micron.

I posted 400x images of the slurry many years ago. Basically... My favored coticules slurry was roughly the same particle size as my 13k synth (~0.7micron or given limitations of my eyesight, I'm comfortable saying <1 micron). I could put it side by side with a thuri, the nicest jnat finisher out there and a Goku 20k and I doubt anyone could tell the slurries apart. A decent modern La Verte was pretty similar to my 6k synth (~2 micron).

 

[cugel]

I like to use slurry on japanese naturals for two reasons: 1) enjoy the feedback provided by working a slurry and 2) water only can be tricky for me; water only on most of my stones requires the lightest touch.

 

[jason12768]

Probably why I find more than one vintage coti and bbw used with oil.
Dem folks of old knew what was up.

 

[kohalajohn]

I put coticule slurry under a scope and the good ones garnets are nowhere near what the commonly believed coti garnet sizes are.

My COARSEST coticules (ones I wouldn't finish on... two vintage 10" stones that cut like coarse sandpaper) had ~12-20 micron particles.

Ones that I considered below avg (a modern LNV) had 5-8micron particles.

Average to Avg+ (Most vintages that don't feel ultra-glassy and the majority of "good" moderns I've owned... a good example would be a fast LV) 1-3 micron particles.

Top notch finishing coticules you couldn't tell the slurry from a 13k+ synth or a Thuri or finishing Jnat. All sub 1 micron.

I posted 400x images of the slurry many years ago. Basically... My favored coticules slurry was roughly the same particle size as my 13k synth (~0.7micron or given limitations of my eyesight, I'm comfortable saying <1 micron). I could put it side by side with a thuri, the nicest jnat finisher out there and a Goku 20k and I doubt anyone could tell the slurries apart. A decent modern La Verte was pretty similar to my 6k synth (~2 micron).

May I ask what microscope you have?

 

[SliceOfLife]

Those pictures were probably with my old wesco 400x

I have an Olympus 800x trinoc now.

 

[kohalajohn]

Slice (and I'm John btw) what would you recommend for a microscope? I'm thinking of upgrading my wee fifty dollar amazon device.

 

[Adonay]

One question for experts. Rinse water in the coticule as in the jnat, or dip the coticule in the water?

 

[SliceOfLife]

The Olympus is definitely overkill. Depth of field is so low at 800x I don't like to use it, and stick to 400x most of the time anyway.

Any decent fully optical 400x should work well. Old high school/college lab scopes (metal, not the plastic toy kind) are a good deal if you find a closeout place selling them. What's way more important is that the platform works well with a razor and that you rig up a very adjustable lighting source. I'm using a ring light on a flex neck.


Wesco on left. I paid <$100 for it 10 yrs ago. Seen them for like $25+shipping if you look/wait.

Olympus on right was $200 or $300 iirc. Previous owner had done a bunch of mods to it to use it kind of like a metallurgists scope. I bought some additional lenses for it as well.

 

[kohalajohn]

Very nice, thx

 

[hobber]

my finishing on jnat hard asagi is simple. do this only if the razor is already shaving arm hair. generate a light koma haze slurry and do a bunch of x-strokes. after the koma starts to dry out and actually starts to break down, i rinse the stone and use toma nagura (same hardness as asagi) or a huffed out 1200 atoma and do a bunch of x-strokes. then, i rinse all slurry and finish on the asagi itself under water. unbelievable edges if you get all the scratches out at each stage. like, surgical sharp...almost too sharp. extreme care must be used to not apply too much pressure while shaving, else you end up with candy cane looking shave cream on your face.

my finishing on the what i like to call any of "the great coticules" (Les Latneuse, La Veinette, La Petite Blanche, and La Dressante), my process is equally as simple. if the razor can already shave hair without pulling (but maybe is still scratchy), go to finishing as follows. rinse all slurry off the stone. using a same vein slurry stone, achieve a very light misty-haze slurry and do circles or x-strokes in same number with light pressure. finish on this light misty-haze slurry with a bunch (25 to 50 for most steel types) of x-strokes to even up the edge. rinse the stone completely, and finish with light x-strokes only with only weight of razor, very delicately. LV (old Preu or new production) and LD (either upper or lower layers) give the best results on this last step. the hybrid side of a nice Les Lat is amazingly fast and will rival the best jnat edge in terms of sharpness, though maybe not as comfortable a shave as a LV or LD final edge.

 

[Biglo13]

i agree that les lats is closest to jnat, generalization. still you have to judge each specific stone on its own merits. just because stone has fancy name, lineage, provenance does not prove stone quality or ability. here is something to try a few uber light laps on dry stone.......

 

[hobber]

i agree that les lats is closest to jnat, generalization. still you have to judge each specific stone on its own merits. just because stone has fancy name, lineage, provenance does not prove stone quality or ability. here is something to try a few uber light laps on dry stone.......

biglo13, i couldn't agree more! this is especially true with jnats and all the probable fake stamps that are put on the stones these days. i mean, how many true "Nakayama" stones are really floating around out there at any given time? probably not as many as ones claiming to be on auction sites. for instance, i have a no-stamp, no-frills kiita which i purchased and had to cut the corner off of for a tomo nagura due to a very small crack being toxic, and i would put the edge it produces up against just about other jnat i own. a truly fantastic stone and one i shall never part with! it also happens to be one of the least expensive jnats i have ever purchased. lucky me, i suppose!

your statement holds true also with coticules. i have glued cots which have no identifiable vein or characteristics which would even lead me to a good guess as to which layer they are, but they sharpen any razor i have honed on them and produce wonderful comfortable shaves pretty efficiently. and, i have a few natural cots with lineage and layer-specific identifying characteristics which have proven to be "challenging" to get a good edge (La Nouvelle, in particular).

to gamma's point above, what is important is that we have stones that we can use effectively to produce the desired level of sharpness on whatever we're trying to sharpen, regardless of all the other stuff that gets us coticule fans' juices flowing.

my thoughts are...buy a few jnats and cots that look/sound good, try them out, keep the ones that work, and pass along the ones that don't. i have a particularly hard time with the latter.