I think I just made a useful discovery, at least a quick google didn't find anyone else writing about it.
I like ceramic knife sharpeners, but wanted something really small for an EDC tin.
Step up the ceramic lathe turning insert:
https://www.ceramtec.com/spk-cutting-mat...-ceramics/
I just bought (ebay) a pack of these, the square shaped type with the dimple in the middle, top middle of picture. £1 each, posted.
They are a little bigger than an aspirin. The flat faces will bring your knife to a razor edge, the sharp edges will cut metal off, for remedial work.
They also scratch glass easily, and as you'd expect they cut metals. I have no doubt they would smash toughened glass but I haven't tried it.
The dimple type are easy to hold, for something so small.