Ceramic stones; what are they exactly?

[JohnPW]

At college we have several stones:
coarse diamond stone, the usual type with a grid of small circles on the top,
medium steel block with diamond particles on the top, with one continous surface,
and fine and extra fine ceramic stones which are actually Spyderco, like this pic

But what exactly are they? Spyderco's website doesn't say anything about what they're made from. They are glass-like to the touch and the blade just glides over them.

 

[bugbear]

Spyderco are Alox abrasive particles (Al2O3) AKA Corundum AKA Sapphire. The bonding agent is ceramic.

I suppose it's unusual that the stone is named after its bonding agent, not the abrasive.

BugBear

 

[JohnPW]

Aluminium oxide, as in man-made india stones? I thought it might be diamond or some high tech stuff. Maybe the high tech is in the ceramic binder.

 

[bugbear]

Aluminium oxide, as in man-made india stones? I thought it might be diamond or some high tech stuff. Maybe the high tech is in the ceramic binder.

Synthetic Sapphires not fancy enough for ya' ?

Don't underestimate the importance of the binder; it's the main differentiator in the (large) world of synthetic water stones.

Binder behaviour is very important to the working of a honing stone, which is why good natural ones are so rare.

BugBear

 

[Cheshirechappie]

I use a couple of ceramic stones, and like them. They cut quite fast, and since they're not too large are easy to store. The manufacturer says they can be used dry, but I found they tended to glaze with metal particles if used dry. I lubricate mine with water having a drop of washing-up liquid added to kill the surface tension, and that floats the metal particles off nicely. The ultra-fine stone has one face ground flat, but my other stone, a medium, is not really as flat as some would like. I find it's quite OK for normal sharpening of edge tools, but I wouldn't trust it for preparing plane iron or paring chisel backs.

On the plus side - reasonably fast cutting, easy to keep clean, hardly wears at all, easy to store, easy to use at the bench (don't need a seperate sharpening station), can be cleaned by rubbing with a panscrub in hot soapy water, or slung in the dish-washer.

On the minus side - very expensive in first cost, the medium stone isn't dead flat, the plastic box they come in may not stand the rigours of hard site use.

 

[MisterInquisitive]

I've got those, there are advantages and disadvantages. They're very hard and don't dish like water stones with softer binders. On the other hand, the examples I got didn't come perfectly flat so I had to flatten them with a diamond plate. This is easier with the medium stone, the fine and ultra-fine not so much. They cut quickly and get clogged quickly, especially on the medium stone, but it's easy to clean them with a scrubber pad and an abrasive cleaner. The fine and ultra-fine stones put a beautiful mirror finish on edges. I use the ultra-fine for my straight razors. Another point in their favor is that they are good at sharpening a variety of tool steels such as HSS, A2, and presumably Veritas's PMV-11 (sp?). I don't have experience with that last one but I've surmised from other forums that the Spydercos play well with that steel.

I'd think of them as oil stones that use soap/water instead of oil. Good for gouges because they don't dish (Spyderco also makes slips). Wish they came in larger sizes and that they were finished flat; they were originally for pocket knives, which don't necessarily require the same degree of flatness as a plane iron. Quite suitable as a substitute for a translucent Arkansas. Certainly more consistent and possibly less expensive. As always, you should follow with a strop. If you have access to them, use them and see what you think.

 

[Sawyer]

I bought a Spyderco 'medium'. It's good but 'medium' is not what I'd call it. It imparts an almost mirror finish and cuts far too slowly for 'medium' sharpening.

Is this normal, or did someone put a fine stone in the wrong box at the factory?

 

[MisterInquisitive]

If it's brown it's medium. I'd agree that the medium and fine are closer together in coarseness than with other media, such as oil stones, and that you can't really do much grinding with the medium. They're more finish stones. But if you use a grinder or coarse sandpaper to get pretty close to your initial shaping, the medium should acquit itself pretty well. In a pinch you could probably just finish off with the medium, but I wouldn't want to do heavy lapping with it. The ultra fine really puts a mirror finish on knives and tools. A trick an acquaintance taught me was to let the UF get clogged with swarf to make it a much finer polisher for straight razors, so I keep mine kind of dark for that purpose.

 

[bugbear]

I bought a Spyderco 'medium'. It's good but 'medium' is not what I'd call it. It imparts an almost mirror finish and cuts far too slowly for 'medium' sharpening.

Is this normal, or did someone put a fine stone in the wrong box at the factory?

Coarse, medium and fine are not very useful terms, since they vary so much in the minds of both speaker and listener. Whilst there's more to a sharpening medium than particle size (see my comment above), particle size is the most important single factor, and knowing it is very helpful.

BugBear