Natural Stones Approximate Grit

[gssixgun]

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 ??

[Bill31521]

I have a few jnats that can deliver absolutely wicked sharp edges. Keener than what I could get off a suehiro 20k easily. And that's like 1/2 micron abrasives iirc.

[Longhaultanker]

Glen, I voted for 10k, but who knows. We’ve been told so many times making such comparisons are unwarranted, apple / oranges. What I’ll confidently affirm is my Arkansas hard black and translucent deliver an “ultra fine,” keen edge. The Zulu Grey ain’t too shabby either. Do these natural stones deliver an edge as keen / sharp as my Shapton Glass 30k? Yes. Maybe I should change my vote.

[Steve56]

Glen, is this a trick question after everyone telling us for years that naturals have no grit rating, lol.

I said 30k because the Gok 20k (which I have) and Shapton 30k (which I don’t have) are rated at 0.5 microns and 0.49 microns. I’ve tried a Shapton G7 that’s 0.44 micron but it was defective, it shed chunks about 200 grit, lol, so no verdict there. I have jnats that can equal the Gok fairly easily. As far as exceeding it, yes in smoothness, but maybe not a lot. So the best jnats that I have, 20-30k synth equivalent, maybe a little more if you factor in smooth.

[Gasman]

Ive gotten 20k compareable results from a jnat. I just wish i could get it more often.

[Brontosaurus]

I've always been cautious not to assign JIS grit ratings to natural stones, and I don't have a lot of experience with high-grit synths. But for what it's worth, what follows is from my experience in honing razors over the past nine years. YMMV and all that. Thus far, I have succeeded in not falling down the Jnat rabbit hole as I don't use slurries and like to use oil when the occasion arises.

I go by the edge that results: does it "get me there" followed by stropping with plain leather?

The only high-grit synth that I've tried, a Sigma Power 13k, has done the trick for me. Naturals and pastes that have worked are as follows: A.J.'s Welsh purple slate (which he rates at 10k-12k); A.J.'s Welsh "Thuringian" (which he rates at 12k-15k); Vermont slate (green, mottled, and purple); Rhode Island whiteheart; black hard, true hard, and translucent Arkansas (here I think a grit equivalent is especially difficult as these stones, when polished, seem to be burnishing the edge as much as sharpening it); Charnley Forest (similar to Arkansas in effect); Solingen red crayon paste (nominally rated at 2-4 microns); and Solingen black crayon paste (nominally rated at >1 micron).

Some hones, stones, and pastes that have come close but not quite worked for me as finishers are as follows: King 8k, Naniwa SS 10k, most coticules (often nominally rated at 6k-8k), Thuris (usually considered a bit finer than a coticule), Rozsutec (an interesting sandstone nonetheless when smoothed), Water of Ayr, and the Thiers-Issard alox-diamond crayon (nominally rated at 10k). All of these hones or stones will result in a nice edge for me if followed by Solingen red- and/or black-pasted strops.

If I take the Sigma Power 13k, the King 8k, and the Naniwa 10k as my JIS references, I would infer that a natural or paste in the equivalent range of 12k-15k gets me there, whereas a natural or paste in the equivalent range of 8k-10k comes close, but not quite enough. One exception would be the red Solingen crayon, which is rated coarser but improves a coticule edge. Perhaps that's because the spine-leading pass is less aggressive? Grit ratings higher than 12k-15k don't really concern me in the same way that achromatic magnifications much above 10x are overkill in my opinion. The shave test, based on human sense and limitation, is the final arbiter.

Given the choices in the survey, none seems to consider the subsequent effect of stropping on plain leather, which, coming off a stone or hone, changes the edge's character significantly. So if I say that sharpening or honing within an equivalent range of 12k-15k gets me there, subsequent plain-leather stropping would seem to blur this distinction, rendering a nice edge off 12k or 15k regardless of the difference in sharpness between the two. And if my honing and plain stropping were really that of a virtuoso, I suppose I could blur that distinction even more, meaning that a nice edge could be obtained off hones and stones in an equivalent range of 8k-10k (i.e., great honing raises that threshold and great stropping lowers that threshold until they overlap).

P.S. After all that, I voted for 12k. Stropping takes this higher,in effect, but much above 12k seems more about microscopy than it does about shaving IMO.

[onimaru55]

This topic is really not helping my headache.. I guess if anything is possible, absolute highest could be 50k + but I'd argue the stone wouldn't be homogenous at that size.

[cliveruss]

I vote 8k for naturals!

A 10k Gokumyo makes a shiny surface by comparison.

Here is a photo of a few stones, a razor, two kamisoris, a piece of 2000 abrasive paper and some oil.

I estimate my natural's grit from looking at the bevels after sharpening, with a high resolution 10x loupe. The surfaces of the bevels all look about the same to me. These are all great finishing stones and the bevels look different from the finish off synthetic stones.

I can not shave directly off any 8k stone (that includes my natural stones). It takes stropping to get a shaving edge for me.

BUT, the action, and effect, of the different stones is significant.

A synthetic 8k stone like a Chosera is very fast cutting. The scratch pattern is regular and the scratch grooves are deep. It also makes a wicked burr which does not come off with stropping, so the shave is nasty.

By contrast, my natural stones grit does not cut as deeply. The grit seems to scrape a wider, thin layer of steel off the surface. The big difference in my experience is that when using slurries with Coticules, Eschers or Jnats, the slurry seems to remove the burr as it sharpens the bevel ... but the slurry also dulls the edge. The final few laps without slurry slowly put a sharp edge on the blade, but the edge still has to be polished on a strop.

My preference is to use Arkansas stones because they are all cutting surface (no mud!) and a few drops of light mineral oil (no stink) work well for me. If I take an edge that has been prepared by a fast cutting synthetic, say 5-8k, the Ark will smooth the bevels and edge, but as there is no slurry, a burr is created too (barely visible, but it glints in the light when looking through my loupe). I remove the burr by wiping a piece of abrasive paper, very lightly, along the edge. In the photo, there is a small piece of 2k paper which I use with a drop of oil. It takes two or three wipes (very light) before the burr is completely removed so that the paper no longer grabs bits of burr. I can feel the difference. Once the burr has been removed, the edge is no longer sharp enough, so I make a few more light laps, maybe ten, to make a new edge which also has a new burr, but it is very small (insignificant).

I then polish the bevels (and edge) with the small stones shown in the photo. They are Gokumyo 10, 15, and 20k. They polish the misty bevels to a high polish quickly, also refining the edge.

This is a good edge to take to a strop. I have made a loom strop (limited sag) which I pasted with 0.25µm cBN. A few light, slow laps on the strop polish the edge to make a fantastic, durable, smooth edge for shaving.

Once I have a good edge, I seldom use a stone again. Stropping keeps the edge for a long time with a good razor. If necessary, a few light strokes on an Ark, followed by the Goks and strop take very little time or effort to restore the edge.

It makes no difference which natural stone I use. None gives me a shaving edge straight from the stone. I am really shaving off the polished edge from the strop.

I have tried some of the vitreous stones, like Jade, Jasper and agate. It looks like they polish the bevels by burnishing, but a leather strop does a better job of polishing the edge for me.

My favorite finishing stones are hard Arks, used with light oil. They are rated at about 1200 grit by Dan's, and I find there is almost no difference between the black, translucent and hard for practical purposes. They are all great.

I enjoy the variety of using other stones. I bought a really nice Jnat, from Alex Gilmore, that feels very nice when lapping. An Escher or Coticule with a thinning slurry is also very satisfying to use. The techniques are slightly different, but they all give me the roughly 8k smooth finish that polishes to a keen edge for the pleasure a smooth, painless shave.

[Pithor]

Coticule and Thüringer: 20.000, at least.

For reference, I have shaved with a few Suehiro Gokumyo 20.000 edges, and found they were the same level of sharp and smooth as my coticule and Thüringer edges. Did not last as long, though.

Regards,
Pieter

[outback]

@Cliveruss.

I'm with ya on the strop.
Something I've added to my stroppin, was to start on a linen strop coated with lead, before going to leather. This is only done, after a honing session, or touch- up.