Rescues · TO SHARPEN
The knife is no sharper after long effort on a stone.
Why it happens
The angle was not held, so metal was removed from the shoulder rather than the apex. Consistency matters more than pressure or time.
Recovering it
Almost any knife short of a broken tip is recoverable — a badly damaged edge is re-established on a coarse stone and then refined, which takes patience rather than skill. The failure that is not recoverable is a knife ground repeatedly at the wrong angle, which eventually changes the blade's geometry. Given how rarely genuine sharpening is needed, the honest advice is to hone often, sharpen occasionally, and never cut on glass or stone.
The mechanism
A knife edge is two ground faces meeting at an apex a fraction of a micron wide. Two different things go wrong with it. In normal use the thin apex rolls to one side; the metal is all still there, just bent, and running the blade along a honing steel pushes it back into line. That is honing, not sharpening, and it is what most people mean when they say they sharpen weekly. Actual sharpening removes metal on an abrasive stone to re-form an apex that has been worn away or chipped, and it is needed far less often. Cutting force rises steeply as the apex widens, which is why a blunt knife is dangerous: it needs more pressure, and it slides off a surface instead of biting into it, with your hand behind all that force.
The full TO SHARPEN lesson — how to tell, where to practise it, what it carries to.