Choosing a Whetstone: Japan's Sharpening Stones

Most people buy the knife first and the stone as an afterthought — usually a wide, cheap combination block that sits in a drawer until the edge has gone properly dull. It is the wrong order. A toishi (砥石) is the thing that keeps a Japanese knife the knife you paid for, and choosing one is much simpler than the shelves suggest. Here is what the numbers mean, how many stones you actually need, and the two habits that decide whether a stone lasts a decade or a season.

The short answer

• One medium stone does almost everything. A #1000 is the everyday sharpening stone. If you buy nothing else, buy that.
• Check whether yours needs soaking. Some stones go into water until the bubbles stop; others are splash-and-go and shouldn’t sit submerged. Follow the instructions that came with the stone, not a general rule.
• A dished stone can’t sharpen straight. Flatten it with a mennaoshi stone and the rest of your technique starts working.

What the grit numbers mean

Stones are graded by the size of the abrasive particle, written as a number with a #. Lower is coarser and removes more metal; higher is finer and refines what’s already there. Japanese stones are generally numbered on the JIS scale, and abrasive scales from other regions don’t map onto it one-to-one — so compare numbers between Japanese stones rather than across systems.

Japanese has three plain words for the three jobs:

• 荒砥石 arato — the coarse stone. It removes metal fast. Its job is repair: chips, a badly rolled edge, resetting geometry.
• 中砥石 nakato — the medium stone. This is where sharpening actually happens, and where a home cook lives.
• 仕上げ砥石 shiageto — the finishing stone. It polishes an edge that is already sharp into a keener, cleaner one.

Where the boundaries fall depends on who you ask. KAI, one of Japan’s large knife makers, puts them at roughly #300–400 coarse, #800–1000 medium, and #2000–3000 finishing. Specialist stone makers extend the top end much further — Naniwa’s catalogue runs from #220 up to #12000. Both are right; the fine end is a matter of how far you want to chase polish.

The useful thing to hold onto is the ratio, not the label. When you step up through stones, roughly doubling the number each time keeps the progression sensible: #400 → #1000 → #3000. Jumping from a coarse stone straight to a very fine one just means a long time spent erasing scratches.

How many stones you actually need

Combination stones are a reasonable way to start — the trade-off is that they are usually thinner per side and wear out of flat sooner. A single thick #1000 is the better long-term buy if you only want one thing.

Skip the pull-through gadgets entirely. They tear a hard Japanese edge rather than cut it, and the damage takes a coarse stone to undo.

Soakers and splash-and-go

This is the one place where a general rule will damage your stone, so it’s worth being precise.

Stones that need soaking go into water until the bubbles stop rising — commonly around ten to fifteen minutes, depending on the stone. A saturated stone holds a slurry, cuts faster and doesn’t dry out mid-stroke.

Stones that don’t are wetted at the surface and topped up with water as you work. Splash-and-go ceramic stones are made this way, and leaving them submerged for long periods is not what they’re built for.

Tojiro’s guidance is the sensible version: soak for the time the maker specifies, and note that some modern stones don’t need soaking at all — but every stone needs water on its surface throughout sharpening. Their practical test for whether a stone is wet enough: after you tip the surface water off, the face should still look damp for 20 seconds or more.

While you sharpen, don’t rinse away the grey slurry that builds up. That togi-jiru is doing part of the cutting.

Keeping the stone flat

A whetstone wears where you use it, and nobody uses the whole face evenly. Over months the middle sinks and the stone goes concave — “dished”. On a dished stone you cannot hold a consistent angle no matter how good your hands are, so this quietly undoes everything else.

The fix is a 面直し砥石 mennaoshi toishi, a coarse flattening stone (or a diamond plate) rubbed across the wet face until the hollow disappears. A pencil grid scribbled on the surface first makes it obvious when you’re done — flatten until every line is gone. Do it often and it takes thirty seconds; leave it a year and you’re grinding away good stone.

A nagura is a different, optional tool: a small stone rubbed on the face of a fine finishing stone to raise a slurry and refresh the surface. It’s most useful on natural and very fine stones, and not something a #1000 owner needs to think about.

Storing it

Stones are more fragile than they look, and most of the damage happens in the cupboard rather than at the sink.

1. Wash it and let it dry fully in the shade. Airflow, no direct sun.
2. Don’t wrap a stone in a wet cloth. Tojiro warn that prolonged damp wrapping degrades the stone itself — abrasive shedding, cracks, splits.
3. Don’t dry it fast or hot. Sun and heat are as bad for a stone as they are for a wooden board.
4. Don’t leave a soaked stone somewhere it can freeze. Water in the pores expanding is a known way to crack one.
5. Keep its box. The original case or a wrap protects the corners, which is where chips start.

A word about natural stones

Before synthetic abrasives, Japan sharpened on quarried rock, and the finishing stones of the Kyoto region — awasedo — were the ones craftsmen prized. Kameoka, just west of Kyoto, produced both awasedo and Tamba aoto, stones that the region’s Natural Whetstone and Hone Museum credits with supporting swordmaking, cuisine, architecture and crafts over a long history. The museum is free to enter and lets you sharpen on stones from across Japan and the world — a genuinely unusual thing to be able to do.

Natural stones are beautiful and each one is its own character. They are also expensive, variable, and demanding to learn on. Nothing about them is required for a sharp kitchen knife. Buy one when you already sharpen well and want to go further — not as a first stone.

How to choose

One rule underneath all of it: the stone is a tool that also needs maintaining. A flat, wet #1000 in the hands of a beginner will out-sharpen a shelf of expensive stones that have all gone hollow.

Not sure how to hold the angle yet? See caring for a Japanese knife, and protect the edge you’ve made with the right cutting board. Or browse hand-picked, Japan-shipped blades on The Table.

Sources & Further Reading

• KAI — Sharpening with a whetstone (FAQ, Japanese) — The maker’s grit bands for coarse, medium and finishing stones, soaking until the bubbles stop, working to a burr, and why a dished stone must be flattened first.
• Tojiro — Handling a whetstone (Japanese) — Maker guidance on soaking to the stone’s specified time, the 20-second surface-damp test, why stones go out of flat, and how to dry and store one without cracking it.
• Naniwa Abrasive — Sharpening Stones — A specialist stone maker’s full lineup, showing the real grit range available from #220 through #12000.
• Natural Whetstone and Hone Museum, Kameoka — A free public museum for Japan’s natural stones, on Tamba aoto and awasedo quarried in Kameoka and their role in swordmaking, cuisine and architecture.