Stays sharp for years, never rusts, and chips if you drop or twist it.
Also called: zirconia blade, zirconium oxide
Measurement
Far harder than steel, near 9 on the Mohs scale
The basics
What to know about ceramic
A ceramic blade is not metal at all. It is a fired mineral, close to the hardness of sapphire. That is why it holds an edge many times longer than steel. It can go a year or more of light home use without attention. Rust cannot touch it, acid does nothing to it, and it adds no metal taste to delicate food. Mohs is a scratch scale of 1 to 10, where diamond is 10 and knife steel sits near 6. Little in a kitchen wears it down.
That hardness is bought with brittleness, and the trade is much sharper than it is with steel. A hard blade rolls or chips; a ceramic blade breaks. Dropping it on a tile floor or twisting it in a squash can take a piece out of the edge. So can hitting a bone or a frozen center, or levering with the tip. Any of them can also snap the point off outright. Cut on wood or plastic, never on glass, stone or a plate, since two hard surfaces meeting chip the edge in one stroke.
It also cannot be brought back at home. Steel sharpeners will not touch it, so a dulled or chipped ceramic knife goes to a service with diamond equipment or goes in the bin. Treat it as a second knife for clean slicing of fruit, vegetables and boneless food, and keep a steel knife for everything else.
Set beside a stainless blade of the same shape, ceramic weighs about a quarter less, which most people read as delicate rather than nimble. Look along the edge under a lamp every few months. Tiny white nicks show first. They turn a clean slice into a tearing one before the knife feels blunt.
How it is made
How ceramic is made
Ceramic blades are made from zirconium oxide powder, pressed into a blade shape under high pressure. Next comes sintering, meaning the shape is fired at over 1400 C until the particles fuse into a single dense solid. The blank comes out of the kiln slightly shrunken and extremely hard.
Because nothing softer will cut it, the edge is ground on diamond wheels. This is also why resharpening needs a workshop rather than a stone. The black versions are fired a second time in a controlled atmosphere, making the material a little tougher and less likely to chip than the white ones.
Best for
When it works well
Slicing fruit, vegetables and boneless meat, where nothing hard ever meets the edge.
Cooks who will not sharpen anything, since a year of light use passes before the edge fades.
Kitchens where rust or a metal taste is a problem, as a fired mineral reacts with nothing you cut.
A second knife beside a steel one, rather than the only knife in the drawer.
