What Is a Burr in Knife Sharpening?

A burr is a very thin lip of metal that folds to the opposite side of the edge while you sharpen. It is useful because it can confirm that your sharpening has reached the apex, but the burr itself is not the finished edge.

Why does a burr form?

As abrasive removes steel from one side, the two planes of the edge finally meet. Continued abrasion pushes a tiny weakened strip of metal over to the other side.

Do you need a burr?

For many home sharpeners, deliberately raising a small continuous burr is the easiest way to confirm that the entire edge has been reached. Experienced sharpeners may use other feedback, but a burr is a practical learning tool.

How do you check safely?

Never slide a finger along the cutting edge. With dry, careful hands and the knife secured, lightly move a fingertip from the side of the blade toward the edge, perpendicular to it. A burr may feel like a tiny catch on the opposite side from the stone.

Why must the burr be complete?

If you can feel it at the heel and tip but not the centre, that section may not yet have reached the apex.

What happens if you leave the burr?

A large or weakened burr can fold during the first cuts. The knife may feel razor sharp immediately after sharpening and then seem to go dull very quickly.

How do you remove it?

Reduce pressure, alternate sides and finish with light controlled strokes. The exact method depends on the knife and stone progression. Stropping can help with final refinement, but it should not substitute for proper stone work.

See the Sharpening Guide and Honing vs Stropping vs Sharpening.