Ceramic Sharpening Stones                                                        <back to Shop Talk articles list


The last article I wrote was on diamond plates for sharpening. I received a lot of responses wanting to know why I liked diamond better than ceramic stones.

I really don't like one over the other. I like anything that makes a smoother, finer edge.
It came down to this; I'm a clutz. Dropping a ceramic stone on a concrete floor was not good, because it broke into two pieces and chipped to a unusable state. I learned something from this.
 1. Diamond plates are tougher.
 2. Maybe I need a rubber floor.
 3. I need to stop being a clutz.

I saw a person use the backside of a ceramic mug to put an edge on a utility knife. I tried it, seemed to work well but next time I'll empty the coffee out!

What they are made of?
Zirconium oxide’s best mineral for stones. Zirconia is an very hard material, on the Moh's hardness scale, it ranks 8.5 (out of 10), compared to steel which only ranks at 6.5 at most. This is what causes ceramic knives to hold their edge so much longer than steel knives. The more expensive ceramic stones reach almost 10 on the scale, making them almost as hard as diamond.

Ceramic sharpeners can also be manufactured from alumina (aluminum oxide) or silicon carbide in a ceramic bond. Silicon carbide has a rated hardness of 9.5 out of 10. They work well for especially hard knives. Harder than glass, ceramic sharpeners will become darker as they remove layers of steel from your knife. They are resistant to rust as well.

How they are made?
Basically these stones are made from pressed and fired zirconia dioxide which is mined and refined in Australia. The miners refine the zirconia by using the old gold miners method of washing away the lighter materials with water in a corkscrew type centrifuge until the finest zirconia remains. It is then shipped as a powder to a manufacturer who presses it into a mold with a 300 ton press. From there it is fired like our coffee mug in a kiln. The stone is tempered in another lower temperature kiln to reduce its brittleness. The surface is milled with a water cooled diamond wheel to give it a flat surface. Sometimes a logo with grit size is then lasered into the stone.

Advantages & Disadvantages
 Advantages:
•Use them dry.
•Can be cleaned with a pot scrubber and dishwashing soap.
•The fine grits leave a polished edge.
•Hard ceramic stones stay flatter, longer.
•If kept clean, they should last a lifetime.

Disadvantages:
• Usually only available in fine grits, so you will have to have a rougher stone to supplement sharpening.
• Course grits fill up over time and don't work as well.
• They can be as brittle as glass, don't drop one or you will have two stones!

Cost Comparison
Overall, In my searches, a ceramic stone is about 10-15% more expensive than a diamond stone. I compared a dual grit DMT stone to dual grit Japanese ceramic stones of the same size.

Well, there you go.
Keep it sharp and keep carving.

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