Sintered ceramic stones

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Barmaley

Joined
Dec 31, 2016
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I used Norton Crystolon which made my kitchen knives sufficiently sharp to do everyday cooking. Recently I bought a complete set of cheap Chinese waterstone (400 to 8000 grit). I was blown away with the pleasure I felt just using them. Obviously I got a serious improvements in the sharpness of the knives. As Rumsfeld ones said sometimes we do not know what we do not know. I wish I would buy the waterstones sooner!

I heard good things about Spiderco ceramic stones but they seems not to be too popular or may be not as popular as waterstones. Am I missing something that I did not get them in fine and extra fine ( I do not care about medium since my diamond plate and Crystolon do cover that niche nicely). Since the only knives I care to sharpen are kitchen knives I do not need grid higher then 2000. How sintered ceramic stones compare to waterstones?

Why are they so expensive? A ceramic tile for floor made of the same material costs somewhere between $0.49 to 2.50 at Lowe's retail. Are there other brands of ceramic stones besides Spyderco?
 
Your Lowes comparison is kinda apples to oranges. Any sizeable tile job, you’ll need hundreds of tiles plus mortar, grout, spacers, maybe tools…

And it’s the color/pattern side that has to match perfectly. Whereas, a ceramic sharpening stone needs uniform grit size.

That said, I have touched up my razor knife on a scrap of bathroom tile. In fact, I’ve even cut rods and tapers from scrap tiles to fit certain abrasive tasks. But I can’t brag about it to BF members, they’ll think I’m a giant cheapskate.

They’ll be right.

Parker
 
They are great for setting the apex with edge leading strokes, which because of their strong bond will not release abrasive that can impact the apex and dull the knife at the same time you are sharpening. This also works against you in that you can get burr formation because there is also no loose grit impacting the apex to remove/reduce the burr at the same time it's being introduced. Abrasion will be slow and at some point they will need to be reconditioned to rough surface (not for the faint of heart).

If you remember to only use these stones as the last step in sharpening after you already have an edge that is near being apexed or burred and deburred, then you will likely be quite happy with them. That said, they don't come flat in general and lapping them is a nightmare unless you have something like a Nano Hone Diamond Button Lapping Plate (NL-8 or NL-10) which cost quite a bit to obtain (though well worth the cost if you lap sintered ceramics or other very hard stones like Arkansas/Crystolon/India).
 
Sintered ceramics like Spyderco's hones are at their best for the final finishing stages in sharpening.

Use them with a light touch to minimize burring issues. And ideally, using them with steels that aren't too heavy in super-hard carbides (vanadium carbide in particular) will keep them from wearing too fast or glazing over time. If you prevent that over the longer run, you'll likely never need to resurface or recondition them as mentioned earlier.

Keep them clean. Use a pink rubber eraser to wipe them down after each use, to minimize loading issues with swarf. That'll keep them cutting the steel efficiently. They'll also avoid loading issues if they're kept lubricated for heavier grinding/polishing purposes, which helps to prevent the steel swarf from clinging to the grit.

And these sintered ceramic hones are worlds apart in their makeup and manufacture as compared to something like ceramic tile (or ceramic mugs, flower pots, etc.). Their composition is almost purely aluminum oxide in a relatively uniform grit range & shape (& hardness, toughness, friability), which is much, much more complex and expensive to manufacture, as compared to something like a ceramic tile, which usually doesn't include nearly as much hard abrasive (aluminum oxide), because it serves no useful function in that application. Most other consumer 'ceramics' are made from clay materials largely silica-based in their makeup - silica is about 1/3rd as hard as aluminum oxide - and a lot less uniform or pure in composition. The word 'ceramic' itself is just a reference to the heating/baking ('firing') process used in making pottery, tile & other materials and implies absolutely nothing about the particular materials (minerals, etc) composing the ceramic.
 
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PLEASE show me where you can get sintered ceramic tiles that cheap. :D Sintered ceramic and vitrified ceramics like those used for floor tiles are not the same thing, neither in materials nor in their manufacturing methodology.

Sintered ceramics are best used as ultra-hard finishing stones, whether for final polishing/refinement or for minor touchups. They actually do not have a consistent grain size, and that is by design. They are made by subjecting a fine mix of grains, typically aluminum oxide (but sometimes other materials like silicon carbide) and subjecting them to enormous heat and pressure to cause the grains themselves to fuse together, much like a synthetic version of how sedimentary stone is used. This is different from things like vitrified water stones or India stones, which are a kind of ceramic, yes, but not sintered. They use abrasive grain held together with a binder, typically a feldspar clay, that's been molded and fired much like a brick. While pressure is often involved in these stones, it's nowhere near the tonnage used in the isostatic presses used for sintering.

The best use case for sintered stones is narrow compared to other styles of stones, and they do have some unique care requirements, but they are arguably the very best at what they do. They are exceptional for final finishing, routine touchups, and working pointed instruments that are prone towards gouging vitrified stones.
 
The term "medium" for the Spyderco Medium Stone(s) might make you think of a rather coarse stone. That is not the case. They are so much finer than a Crystolon and would be a good stone after a fine Crystolon. Grand Unified Grit Chart rates the Medium stones as ~ 1.200 JIS. It is a stone for touch ups. Whereas a Crystolon is used to set a new bevel or for edge repair.

Having a Crystolon I think the Medium is much more important than Fine + Ultra Fine. I would rather buy one of the white stones and the Medium instead of Fine and Ultra Fine and not having the Medium.
The step from a Fine Crystolon to a Spyderco Fine would be too big.
 
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The 'jump' from a very coarse stone to a typically very fine sintered ceramic may or may not be an issue. It depends on what your goals are in using the sintered ceramic. If your goal is a higher polish on the full width of the bevels, then the size of the jump is something to take into account. But there can be good reasons to deliberately make that big jump in grit, and get great results.

One of my favorite uses for either of Spyderco's medium or fine ceramics is to apply a tiny, more finely-finished microbevel atop an edge set with a relatively coarse, toothy bite. The 'jump' from something like a Coarse DMT (325 / 45 micron) or even an Extra-Coarse DMT (220 / 60 micron), to the medium or fine ceramic can leave an absolutely vicious-slicing edge with lots of toothy bite from the coarse stone, and a narrower apex width afforded by the finer ceramic. The result is an edge that dives effortlessly into a material being cut (thanks to the narrow apex) and then zips aggressively through it (thanks to the toothy bite behind the microbevel). And the ceramic can work well for just deburring such an edge as well. Nowadays, I rely more upon using a ceramic for deburring, and less upon using a loaded strop. The ceramic will leave a crisper apex which keeps its 'bite' longer than a stropped edge, which tends to become more polished and lose its toothy bite sooner via the loaded strop.

Edited to add:
In writing the above, I realized I value sintered ceramics most for their enhancement capabilities at the very apex of the edge itself. That's where they really earn their keep and work better than most anything else I could think of. Plenty of other options exist for refining & polishing the bevels behind the apex. And for polishing in particular, when I do it at all, I usually prefer a hardwood strop for that.
 
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FYI you have other options other then spyderco for sintered ceramic bench stones. Idahone is slightly less if I recall right and Nortons is much more, I have no experience with either though. If using for kitchen knives a ceramic stick might work for you and will be less then a bench stone, the idahone gets good reviews but there are others like Mac and Chicago Cultery.
 
Papilio said:
The term "medium" for the Spyderco Medium Stone(s) might make you think of a rather coarse stone. That is not the case. They are so much finer than a Crystolon and would be a good stone after a fine Crystolon. Grand Unified Grit Chart rates the Medium stones as ~ 1.200 JIS.
Having a Crystolon I think the Medium is much more important than Fine + Ultra Fine. I would rather buy one of the white stones and the Medium instead of Fine and Ultra Fine and not having the Medium.
The step from a Fine Crystolon to a Spyderco Fine would be too big.
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Rather, I would suggest getting a Fine stone and refinishing one face with coarse lapidary diamond grit. Sintered stones cut more like a file than like sandpaper, so the surface finish has a huge impact on the finish produced.
 
FortyTwoBlades said:
PLEASE show me where you can get sintered ceramic tiles that cheap. :D Sintered ceramic and vitrified ceramics like those used for floor tiles are not the same thing, neither in materials nor in their manufacturing methodology.

Sintered ceramics are best used as ultra-hard finishing stones, whether for final polishing/refinement or for minor touchups. They actually do not have a consistent grain size, and that is by design. They are made by subjecting a fine mix of grains, typically aluminum oxide (but sometimes other materials like silicon carbide) and subjecting them to enormous heat and pressure to cause the grains themselves to fuse together, much like a synthetic version of how sedimentary stone is used. This is different from things like vitrified water stones or India stones, which are a kind of ceramic, yes, but not sintered. They use abrasive grain held together with a binder, typically a feldspar clay, that's been molded and fired much like a brick. While pressure is often involved in these stones, it's nowhere near the tonnage used in the isostatic presses used for sintering.

The best use case for sintered stones is narrow compared to other styles of stones, and they do have some unique care requirements, but they are arguably the very best at what they do. They are exceptional for final finishing, routine touchups, and working pointed instruments that are prone towards gouging vitrified stones.
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Another option for the same role we are talking about here would be something like this. It will not release abrasive at all either and will likely do better across the widest range of steels. Can you think of any reasons why this wouldn't be a better choice? I'm looking at picking either this DMT MXF/EEF combo stone or the Norton Ascent Fine and Extra Fine. The DMT route gets you the same grit range at almost a third of the price. Seems like a no brainer but I like the idea of the ceramic for dealing with the high contact pressures that come with using on a micro bevel rather than a much wider bevel, especially at the tip.

www.sharpeningsupplies.com

DMT 8" Double-Sided DiaSharp Medium Extra Fine & Extra Extra Fine

The two finest DMT stones, the Medium Extra Fine 4000 grit and the Extra Extra Fine 8000 grit are now available as a combination stone!
www.sharpeningsupplies.com
 
Barmaley said:
May I ask you to elaborate on the difference of sandpaper cut and sintered stone cut?
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In the case of sandpaper the specific size of the grit directly impacts the surface finish being produced. In the case of a sintered stone the fact that they are made of assorted grit size matters little as it is a combination of the hardness and the shape of the surface finish made by that base material that creates the cutting action, much like how files are essentially a series of little metal-cutting chisels made of a steel harder than the material that they are intended to cut. So too do sintered stones rely heavily on their surface texture, because their bond is so hard that they are a fused solid which does not shed grit like a conventional vitrified bond stone does. A normal vitrified stone is intended to shed grit as that surface layer dulls, to expose fresh sharp grit and a certain natural surface texture which gives you the grit protrusion etc. Because this does not occur, blunting of the abrasive in a sintered stone is like a file's teeth going dull. Eventually you need to deliberately refresh the surface to remove the blunted abrasive grains for it to continue cutting instead of rubbing.
 
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