Vol. IV · Knives, Tools and the Work Space Plate 6 of 10sharpening, honing, whetstone, burr, grit, angle, steelT

Sharpening and Honing.

Honing straightens an edge that has rolled over; sharpening grinds away metal to make a new one. Both depend on holding one angle.

A sharp edge is two flat bevels meeting in a line too fine to see. Use rolls the line over and wears it round. A honing steel pushes a rolled edge back upright, which restores much of the bite for a while. When honing no longer helps, the knife needs sharpening: grinding each bevel on an abrasive stone until it meets the other cleanly. You know you have ground far enough when a burr forms — a thin wire of metal folded over to the far side all along the edge. Then you switch sides, and finally take the burr off with lighter strokes and a finer stone.

The skill is holding one angle stroke after stroke. A small trick of geometry helps: for a blade of a given width, an angle corresponds to lifting the spine a fixed height above the stone. The workshop works it out.

Below: how high to lift the spine above the stone for the angle you want, and how far the angle wanders if your hand wobbles by a millimetre; with the stones a sharpener moves through.

What you will learn
Workshop
Spine height h = blade width × sin(angle). A wobble of 1 mm in h changes the angle by about 1/width radians. Grit numbers are the usual Japanese scale (coarser numbers remove metal faster).

One angle, many strokes

A 45 mm blade sharpened at 15° needs its spine lifted 11.6 mm above the stone; at 20°, 15.4 mm. Stack coins to that height at the start of each session and let your eye learn it. A wobble of one millimetre changes the angle by about 1.3°, and a hand that rocks from stroke to stroke grinds a rounded bevel that is never really sharp. Slow, even strokes at a fixed angle beat fast ones.

Work through the grits: a coarse stone (about 220) only to repair chips or reset a badly worn edge; a medium stone (about 1 000) for ordinary sharpening, until a burr runs the full length on the far side; then switch sides; then a fine stone (3 000–6 000) and very light alternating strokes to remove the burr and refine the edge. Hone on a steel or a fine stone between sharpenings — a few light strokes at the same angle before each session of cooking.

At the stove

Run a fingertip gently from the spine towards and off the edge (never along it) after sharpening one side: a burr feels like a slight catch on the far side. Check that it runs from heel to tip before turning the blade over. Test the finished edge by slicing a sheet of paper held in the air.

Japanese whetstones are soaked in water before use; many synthetic ones are "splash and go". Oil stones were the European tradition. All work by the same abrasion; the water or oil only carries the swarf away.

Terms

Honing
Straightening a rolled edge on a steel or fine stone; removes little metal.
Sharpening
Grinding new bevels on an abrasive until they meet in a clean edge.
Burr
A thin wire of metal pushed over to the far side of the edge, showing the bevel has been ground through.
Grit
The fineness of an abrasive; higher numbers are finer.
Sharpening grinds until a burr forms, at one steady angle; honing straightens the edge between sharpenings.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.