Whetstones and flattening plates 砥石

What is a whetstone, and what does the grit number mean?

A whetstone, or sharpening stone, is used to sharpen the edges of steel tools such as knives through grinding and honing. Wikipedia's entry on the tool explains that stones used with water for this purpose are usually called water stones. Grit is the measure that matters most: Wikipedia's own definition is that grit size is given as a number indicating the density of abrasive particles in the stone, where a higher number means smaller particles packed more densely, giving a finer finish. A low number cuts fast and coarse; a high number cuts slowly and leaves a smoother edge. Traditional Japanese stones are graded a little differently again: Wikipedia sorts them into ara-to, a rough stone, roughly 500 to 1000 grit on a non-Japanese numbering system; naka-to, a middle stone, roughly 3000 to 5000 grit; and shiage-to, a finishing stone, roughly 7000 to 10000 grit, with a nagura block used to raise a slurry on the hardest finishing stones rather than sharpening directly with it.

Do you need to soak the stone, or is it splash and go?

It depends entirely on the stone, and mixing the two up either wastes time or starts you sharpening too dry. Our Imanishi Dragon 800 grit stone is a soaking stone, and our Imanishi Kitayama 8000 grit finishing stone wants about 15 minutes of soaking before use. Naniwa's Chosera and Gouken Arata ranges make soaking optional instead, suggesting no more than about 15 minutes if you do soak, with a spray bottle to keep the surface wet as you work; the listings warn against leaving a Chosera stone standing in water, since it can affect the stone's bonding. Shapton's RockStar range is splash and go: wet the surface and start, no soak needed at all. If you are not sure which kind you have bought, treat it as splash and go first and only soak it if the surface stays dry and dusty once you start.

What do we stock, by grit?

Coarse. Naniwa's Chosera 400 grit stone is rated for establishing a new bevel angle or removing chips from the blade, and the same 400 grit is available in the smaller Gouken Arata format. Medium. Naniwa's Chosera and Gouken Arata both come in 800 grit for routine resharpening, and our Imanishi Dragon 800 grit stone sits in the same band. Mid to fine. Naniwa's Chosera and Gouken Arata both come in 3000 and 5000 grit, and Suehiro's Ouka finishing stone is 3000 grit with its own nagura included. Fine. Naniwa's Junpaku Snow White and Imanishi's Kitayama are both 8000 grit finishing stones, Shapton's RockStar range covers 8000 and 16000 grit and the Naniwa Gouken Arata tops out at 10000 grit. Browse the current range to see what is in stock, since it shifts as pieces sell through.

What is a flattening plate, and do you need one?

Yes, eventually, for the same reason any stone needs one: Wikipedia's entry on sharpening stones explains that a whetstone wears unevenly with use, typically hollowing out in the middle, so a knife sharpened against a dished stone comes out with an uneven edge. A flattening plate or stone, rubbed across the surface, levels it back out. We stock two kinds. Atoma's diamond flattening plates come in 140 grit for coarse, heavier flattening and 600 grit for a finer touch up, both handled so the plate does not stick to the stone as mud builds up between them; a 600 grit replacement abrasive sheet is also available on its own once the original wears out, since the diamond sheet tapes onto a separate base rather than being fixed to it. Suehiro's ceramic flattening stones, in a coarse and a medium cut, are the cheaper option; the listing itself is candid that a diamond plate probably flattens best, but its upfront cost can be more than the waterstone it is meant to true up.

What about a two-sided combination stone?

We don't currently stock one. A combination stone puts two grits on either face of the same brick, useful if you want one stone to cover both a routine sharpen and a finish, but everything we stock right now is single grit. A coarse and a fine single-grit stone from the same range, Naniwa's Chosera line for example, covers similar ground in two stones instead of one.

How does this connect to sharpening and choosing a knife?

A stone on its own does not do much without the technique behind it. Our sharpening a Japanese knife guide covers soaking, angle, burr and flattening in full, stone by stone; our Japanese kitchen knife guide covers which shape and steel you are actually sharpening. Start with a middle grit stone, something in the 800 to 3000 range, if you are buying your first one. Add a coarser or a finer stone later once you know what your knives actually need.

Quick answers

These are the questions people ask us most often about choosing a whetstone, answered briefly.

Do all whetstones need soaking? No. Some, like our Imanishi Dragon and Kitayama stones, are soaking stones; Naniwa's Chosera range makes soaking optional; and Shapton's RockStar range is splash and go, wet the surface and start. Check the specific stone before you buy it if this matters to you.

What grit should I start with? Something in the middle of the range, around 800 to 3000 grit, covers routine sharpening on a knife that is not badly chipped or blunt. Add a coarser stone for reshaping and chip repair, and a finer stone once you want to polish the edge further.

Do you sell flattening plates? Yes. We stock Atoma diamond flattening plates at 140 and 600 grit, plus a 600 grit replacement abrasive sheet and Suehiro ceramic flattening stones in a coarse and a medium cut as the cheaper option.

What's the difference between the Chosera and the Gouken Arata? Both are Naniwa's ceramic stone line and cut the same way; the Gouken Arata, also called the Baby Chosera, is a slimmer 15mm stone without the permanent base or large nagura the full Chosera ships with, sold on a removable box base instead.

Do you stock a two-sided combination stone? Not currently. Everything we stock right now is single grit; pair a coarse and a fine stone from the same range, Naniwa's Chosera line for example, to cover similar ground instead.