Why 400 to 6000 Ruins an Edge

The stones do different jobs

A water stone is not one tool. It is a grit number, and the grit number decides what the stone is for.

荒砥（あらと）means coarse stone. 中砥（なかと）means medium stone. 仕上げ砥（しあげと）means finishing stone. Japanese sharpeners have used this three-part language for a long time, and it maps cleanly onto the numbers you will see in a shop.

| Grit | Japanese | Job | |—|—|—| | 400 | 荒砥（あらと） | Remove chips, set a new bevel | | 1000 | 中砥（なかと） | The working edge. Most of your sharpening happens here | | 3000 | 中仕上げ（なかしあげ） | Refine the scratch pattern | | 6000 | 仕上げ砥（しあげと） | Polish. Push-cutting and clean slices |

Notice that 1000 is called the medium stone, not the coarse one. If you only own one stone, own a 1000.

Soak times are not the same

Water stones are porous. They need water inside them, not just on the surface.

A 400 grit stone is soft and thirsty. Ten to fifteen minutes in a tray of water is normal. A 1000 grit stone usually wants the same, maybe ten minutes. A 3000 or 6000 grit stone is harder and denser — five to ten minutes, and some finishing stones are splash-and-go, meaning you wet the top and start.

If you are unsure, soak it, then watch. A stone that keeps drying out mid-session was not soaked long enough. A stone that has sat in water for a week is a stone you should not have left in water for a week.

Do not soak a natural stone unless you know that specific stone tolerates it. Some do not.

Why you do not jump from 400 to 6000

This is the part that matters.

Every stone leaves scratches. A 400 grit stone leaves scratches that are, roughly, the width of its particles. A 6000 grit stone leaves scratches far finer. The problem is that a fine stone cannot easily erase a deep scratch — it polishes the walls of the scratch and leaves the trench.

So if you go 400 straight to 6000, you get a blade that looks shiny and cuts worse than it should. The edge is a series of deep grooves with polished sides. It will feel sharp on your thumb and catch on a tomato skin.

Going 400 → 1000 → 3000 → 6000 is not ceremony. Each step removes the scratches of the previous step. That is the whole mechanism.

If you are in a hurry, 400 → 1000 → 6000 is acceptable for a kitchen knife. 1000 → 3000 → 6000 is fine for maintenance when there is no chip to remove. What you should not do is skip the middle entirely.

How to tell a step is finished

You need a way to know when to move up. Three signs:

1. The scratch pattern from the previous stone is gone. Look at the bevel under a light.
2. You can feel a burr（かえり）— a thin wire of metal — along the whole length of the edge on the side you are grinding. Run a fingertip across the edge, never along it.
3. The stone stops cutting as fast. That usually means the surface has loaded up with metal, not that the stone is worn out. Flatten it or rinse it.

If the burr runs the full length, the coarse work is done. Move up. If it only appears in the middle, you have more work at that grit.

Yesterday we looked at how to inspect a used knife and log what you find before you touch a stone. That log is what tells you which grit to start at — a chipped blade starts at 400, a blade that just needs refreshing starts at 1000.

A note on flattening

Stones dish. The middle wears faster than the edges, and a dished stone cannot give you a consistent angle. Flatten before a session, not after. A diamond plate or a flat concrete block with wet sandpaper will do it. You will notice the difference on the first stroke.

If you are sharpening in a small kitchen in your city, a sink bridge and a tray are worth the space. Water goes everywhere otherwise.

What the stones cannot fix

Grit progression controls the shape of the edge. It does not control the angle you hold. You can complete a perfect 400 → 1000 → 3000 → 6000 sequence and still produce a blade that will not cut, because the angle wandered while you were doing it.

That is tomorrow's problem.