Best sharpener for ceramic kitchen knives?

[Tim+]

I have a ceramic knife that I use a lot but it?s definitely beginning to lose its edge.

Are they worth sharpening, and if so, what?s the best tool? Diamond file? If so, what grade?

Tim

[jrwalliker]

How about the finest grade of diamond grinding/polishing paste on a sheet of glass?

[Chris Hogg]

Ceramic knives are made of zirconia. It has a hardness of about 9.5; diamond has a hardness of 10. You will need a diamond file, the finest grade you can lay your hands on.

[Brian Gaff (Sofa 2)]

I was given to understand that it was a throw away if it went blunt, but I suppose it might be sharpened, but something hard enough and yet fine enough to make cut smoothly could be hard to find. I wonder how they make them in the first place? Brian

[tabbypurr]

Diamond. A set of 3 in different grits is a good plan.

[Chris Hogg]

(I note that the Wiki article says Zirconia has Mohs hardness of 8.5, not 9.5 as I said earlier. Either way, it's hard!)

A nominally dry powder (say around 2% moisture), usually derived from spray-drying a high-solids suspension, is pressed under high pressure in a mould. Pressures are usually several tens of tonnes per square inch, up to say 50 tonnes per sq. in. Isostatic pressing can be used in place of uniaxial pressing. It is then fired to temperatures typically around 1500 - 1600°C, and subsequently finished using diamond grinding wheels.

[newshound]

I'm half way between you and Chris, I'd use my double sided diamond file, coarse side first!

Interestingly, there is a difference between "polishing" and sharpening by grinding. As I am sure you are all aware, the Moh's scale is based on finding one material that will actually scratch another, and I suspect that diamond will not scratch zirconia.

But you can, actually, polish diamond with a material that is less hard. The surface gets smoothed by a process of deformation rather than material removal, caused at least in part by softening associated with frictional heating. So you may be able to improve the cutting of a ceramic knife with a softer material.

See "Bielby layer".

[The Natural Philosopher]

stropping a razor?

[newshound]

Yes, another good example. Another thing this is doing is removing any little curls of swarf left by the previous process. I think that is also one of the things behind the Ray Mears trick of finishing off a knife blade against the edge of a car window.