Burnishing and Jnats

The Arkansas threads have gotten me thinking about surface finishing, on hard jnats.

If you look across the fora, you’ll get different answers to how fine/smooth a jnat needs to be finished.

You can find posts that say ‘not that fine, in a few strokes it wears down’, or ‘not that fine and smooth it with a nagura’ - which I do for the record. And you can find others that smooth to 2k sandpaper or so, which I also do, well 1500 or 2k, whatever’s out on the bench.

But I have some jnats that are really, really hard. Not Ark hard of course, but with a tomo of equal hardness it will take 3 minutes or so to raise a light slurry with moderate to heavy pressure. They glaze to some extent, like an Ark maybe. I can de-glaze the stone (and nagura) and it works faster, but does a hard, glazed, jnat act finer like a hard burnished/glazed Ark? I think maybe a glazed hard jnat does finish finer than an unglazed one, but thought that I’d throw out this question for the jnat folks. Oz, Stefan?

I feel that on really hard Jnats the stones do benefit from that finer smooth finish. On the ones that aren't that hard you can remove the lighter scratches with nagura from the stone so it is resurfacing itself and fixing those before the blade hits them. On the harder stones not so much. Plus on the harder stones those sharper edges from scratches even the ones you can't see are not giving like a softer stone on that edge. I know there is alot more going on here with the surface friability and hardness too. The nagura with also make a difference of course.

I have to agree from my experience.

Will it work similar to an Arkansas, and polish finer if well burnished? Sure. But every time you rub a nagura over the surface, you're disturbing that burnish by releasing some of the surface grit on the hone whether you're using Tomo or something softer. So...are you willing to burnish your hard Jnat and never touch that surface with a nagura again?

Besides, when you think about it your Jnat will typically be polished according to the nagura you're using in concert with it. Mine stays polished to somewhere in the 4 to 6k range, and that's well beyond what most do to their Arkansas stones.

Ok thinking out loud....

If you are finishing on said stone with water only then yes you may see some advantage to polished jnat.

But I see where you are heading with this... burnish or polish with jnat........ a glazed stone is already “burnished”

Is that hard jnat not producing laser sharp edges, or satisfactory edges as it is?

It can’t hurt to test it. A lapping session really won’t take any years off a hard jnat. Plus I understand you have quite the collection.

I like that you are thinking outside of the box!!!

In my mind:
To an extent yes. (maybe)
The edges off a freshly lapped and somewhat smoothed hard jnat might not be as good as the edges off that same jnat if it had been used for a few months and formed a sheen.
I think that is true or it could be a figment of my imagination.

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Originally Posted by JOB15

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I think that is true or it could be a figment of my imagination.

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That’s about where I’m at!

The problem is that there are too many variations leading up to a Jnat.

The bevel set for one can make a massive difference to the end result. Then ontop of that you have what you feel or think or maybe know because some one told you.

I think that stones have spirits and it more to do with that :)

It’s also good if the honer has some spirits...

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Originally Posted by Steve56

But I have some jnats that are really, really hard. Not Ark hard of course, but with a tomo of equal hardness it will take 3 minutes or so to raise a light slurry with moderate to heavy pressure. They glaze to some extent, like an Ark maybe. I can de-glaze the stone (and nagura) and it works faster, but does a hard, glazed, jnat act finer like a hard burnished/glazed Ark? I think maybe a glazed hard jnat does finish finer than an unglazed one, but thought that I’d throw out this question for the jnat folks. Oz, Stefan?

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So if we're talking uber hard Jnats, like things that barely slurry with a diamond plate then I can't tell any difference in the final result. Such stones can be very slow cutting or sometimes "scratchy" so a bit of slurry can be a benefit. Even with scratches from an Atoma 1200 these stones will still reflect an image so it's kinda splitting hairs to me.

I think you have an apples to oranges thing when you talk Arks & Jnats but no one says you can't purpose a stone the way you wanna.

Quote:

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Originally Posted by JOB15

In my mind:
To an extent yes. (maybe)
The edges off a freshly lapped and somewhat smoothed hard jnat might not be as good as the edges off that same jnat if it had been used for a few months and formed a sheen.
I think that is true or it could be a figment of my imagination.

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In general this has been my experience as well. Whether we're talking about an Arkansas stone, my PHIG, my Jnat, or one of the Welsh slates they do seem to perform better (slower perhaps, but polish better) when they've simply been used for a few months and not lapped constantly for fear of it getting out of flat. Needless to say, at this point with harder stones I lap less, and just let the hone be what it is. If they get out of flat then I'll worry about it. My diamond plates probably appreciate this too, the PHIG really wears those poor puppies out.

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Originally Posted by Marshal

In general this has been my experience as well. Whether we're talking about an Arkansas stone, my PHIG, my Jnat, or one of the Welsh slates they do seem to perform better (slower perhaps, but polish better) when they've simply been used for a few months and not lapped constantly for fear of it getting out of flat. Needless to say, at this point with harder stones I lap less, and just let the hone be what it is. If they get out of flat then I'll worry about it. My diamond plates probably appreciate this too, the PHIG really wears those poor puppies out.

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Makes sense. Finishers shouldn't lose flatness for the few light strokes they get used for.

[I]“They glaze to some extent, like an Ark maybe. I can de-glaze the stone (and nagura) and it works faster, but does a hard, glazed, jnat act finer like a hard burnished/glazed Ark? I think maybe a glazed hard jnat does finish finer than an unglazed one.”[/I]

In theory yes, but, as said they are different stones with different shaped grits, hardness and binders. Jnats are not as hard as Arks, so while the stone can burnish, (the tops of the grit are flattened) grit comes loose and hard loose grit scratches the bevel and can result in edge chips.

I believe a lot has to do with the shape of the grit, and of course the binder. Jnat grit is flatter and therefor not as deeply suspended in the binder.

For this reason, I do not finish on water and use a lite slurry, that acts as a lubricant, preventing scratching and chipping on hard Jnats.

Glazing is different from burnishing, we see glazing, swarf build up on some synthetics, Naniwa Super Stones are notorious examples. That glazing swarf build up keeps the edge off the grit and can edge impact leading to edge chipping. The swarf is steel, grit and binder mixed and bonded to the stone surface. A quick lite lapping removes the glazing and refreshes the stone face allowing it to cut and polish.

Is some of that also occurring on a hard Jnat? Possibly.