How to Sharpen a Japanese Knife on a Whetstone

0:00What you need to get started

Freehand sharpening looks intimidating, but it really isn't. Besides your dull knife, you need a couple of stones — I sharpen on a 1,000 grit medium and a 3,000 grit finisher — plus a spray bottle of water, a paper towel to clean the blade, and something to keep the stone from sliding, an anti-slip mat or a stone holder. One thing to know before you buy: some stones are soakers, the classic King stones being the standard example, and they need a soak in water before you sharpen. The faster modern stones do not need soaking, and in fact soaking will damage them.

your right hand will be responsible for locking the angle of the knife against the stone, so we hold the knife in a classic pinch grip position

2:46The two-coin method

How do you find the right angle? The simplest trick is the two-coin method: lift the spine of the knife and rest it on two coins laid on the stone. That gap is roughly the correct angle for most kitchen knives, and it is the fastest way to check yourself as you set up.

So you put two coins on there. That's roughly the correct angle, like so. So this is one way of determining roughly what sort of angle you are using.

5:15The Sharpie test

For a new knife, the Sharpie method is my favourite. Mark the factory bevel with a permanent marker, then take a few strokes. If the marker barely moves, your angle is too high; if you wipe away a lot, you are mostly scratching the top of the edge. When the whole edge clears to a uniform shine, that is the right angle.

7:18The angle guide

The third option is a physical angle guide, which we give out with some knife purchases here at Knives and Stones. It is fine for setting your initial angle, but I would not keep it on the stone for the whole session. In the end, experience does the work: after a while you simply know the correct way for the knife in your hands.

With experience gained, you would just know that, okay, this is the correct way for this sort of knife. It's, it all comes down to experience.

12:06Sharpen the whole edge

Always sharpen the entire blade, not just the section you happen to use. People do this all the time, and the section they favour gets sharpened a little more every time, until the profile goes flat and then hooks over. If you have seen a colleague's knife with a hooked edge, that is exactly what it is.

17:03The burr tells you to stop

We do not count strokes. The stop signal is the burr — a small wire of metal that forms on the edge once the stone has worked through to new steel. You can feel it scratching your finger, and it is much easier to feel on a 400 or 1,000 grit stone than on a fine one.

19:30Removing the burr

Once the burr has formed, remove it before you flip the knife or move to the next stone, or it will wreck your result. Trailing strokes — edge away from the stone, not into it — take most of it off. Carbon steels release theirs easily; on a stainless like VG10 or Ginsan, a light pass along a paper towel or a piece of soft timber does the rest.

25:44Two stones is enough

For a kitchen knife, a 1,000 grit stone to form the edge and a 3,000 or 5,000 grit stone to refine it is all you need. The 12,000, 20,000 and 30,000 grit stones are completely unnecessary for a knife that cuts vegetables on a hard board — that showy edge will not hold for a few cuts.

well you can certainly use them if you like it, but it's completely unnecessary, as I can totally understand the eagerness when one just started the journey of sharpening

28:52Testing the edge

A well-sharpened knife grips your nail without slipping, and it will slice a sheet of A4 paper cleanly. If a section of the edge catches on the paper, that section is not done.

There are a few ways to test the sharpness of your Edge. One very easy one being the nail test.

31:23Sharp does not mean it cuts

Here is the catch: a hair-sharp edge does not guarantee a knife that cuts well. An axe can be sharpened to a hair-shaving edge, and it will still split a potato instead of slicing one. That is the thinning problem, and it is what part two of the course covers.

0:00How many stones do I actually need?

One question I get asked all the time, either from someone just starting out or someone who's been at it for years: how many sharpening stones do I need? My answer is a small core set. 400 for thinning, 1000 as the everyday starting grit, 3000 as a solid pre-finisher, and 5000 if you want a fast, nice polish (the Naniwa one is good). Past that it's 6000, 8000, 10,000, 20,000, even 30,000 from Shapton, and honestly I don't know what the difference between an 8000 and a 5000 even is. So the list just keeps going, and unless you're super rich, it's not really feasible.

3:02The chipped-knife dilemma

Then one day you look at a knife that's super thick or just got damaged, there's a big chip on it, and even your 400 grit is going to take a long while to thin it. Do I buy a 200 grit stone for that? There's probably not a 100 grit out there. So what people do is grab an Atoma diamond plate or a DMT, and that little guy costs about 150 Australian dollars, 120 US dollars. It may actually cost more than the knife you're trying to fix. That's the dilemma this whole episode is about.

5:36Making a one-off stone from offcuts

Here's the trick I often tell my customers to do. Go to the hardware shop, pick up some plywood offcuts (MDF works even better), cut them to roughly the size of a sharpening stone, or bigger. Cut a piece of sandpaper to match, glue it on with contact adhesive or spray glue, put some weight on top and wait for it to set. Now you have a one-off base for a one-off sheet of sandpaper. Want to try a 20,000 grit for once? Or a very coarse paper to thin a broken knife? There you go, without buying a full stone.

Cut them into whatever size they desire, similar to a sharpening stone.

7:48The clamp that holds the sandpaper

If you don't want to wait on the glue, the shop sells a sandpaper holder that clamps loose sandpaper drum-tight. Once you clamp it, it generates a tremendous amount of tension, which is super important because when you're sharpening, it's very easy to push the sandpaper around. That's exactly why we have to glue them down in the first place.

Because when you are doing sharpening, it is very easy to push the sandpaper, that's what we have to glue them.

9:58Putting the 80 grit to work

Let's see how this one-off stone performs. First up, the 80 grit. As you can see, it's already flattened half of the Naniwa 8000, and it takes pretty much no time. If that feels a bit too coarse, you can go on to 200, even 400, to remove the deep scratches. The point is, because the water hasn't really penetrated through the material yet, it is more than enough, and it's very, very flat. So if you want to use it as a flattener or a thinner, you don't have nearly as much problem as a softer 300 or 400 grit stone that dishes really, really quick.

It takes pretty much no time for this 80 grit sandpaper stone to be able to flatten this naniwa 8000.

13:14Bottom line

After doing the test, I believe you have now seen that these one-off stones actually work quite well in their designated situations: thinning, refinishing, and flattening. And if you want to try out some of the grits you haven't tried before, this is definitely a good way to save you a few bucks. Of course you would not be able to replace an actual stone, because they do have different feedbacks, and the grits on sandpaper sometimes differ from the grits on a stone. But as a trick to get away with "I just need this stone and I don't have it", it works.

0:00The knife that looks sharp but won't cut

This one is a customer's knife, and it looks sharp enough, but it cannot cut at all. Years of abuse from the owner — it has been run through machines, and now it splits potatoes instead of cutting them, leaving a rough, uneven surface.

while the knife looks sharp, it cannot cut at all, that's because of years of abuse from the customer

3:05The potato test

To see the difference, I cut a potato with the problem knife and a new showroom knife as the control. The new knife slices through easily, and the cut surface reflects the light — a smooth cut, no problem. The problem knife has to force its way through: the surface comes out rough, and the blade wedges badly, thin on one side and thick on the other.

5:04Why it won't track straight

The difference between the two blades is the cladding line. On the new knife the core is exposed, and that is where the hard steel does the cutting — this is a clad knife, soft cladding on the outside, a hard steel core inside. On the customer's knife the core is gone: years of sharpening have removed it, and the knife has never been thinned at all.

7:48The fixed-angle problem

Over the years, knives get run through fixed-angle sharpeners, and that is the problem: none of them can thin the knife. And if you want to preserve the performance of a knife, you have to thin it.

they all have this similar problem, that is, you can't really thin the knife

9:41How the shoulder builds

A new factory edge is ground properly thin and sharp. Every time you sharpen, you lift the knife up at an angle, and over the years the angle stays the same. That builds a shoulder — a thick wedge of metal right behind the edge — which ends up pushing the potato instead of cutting it. That is the biggest problem.

11:38Sharpening vs thinning

Sharpening lifts the knife up at an angle; thinning is the opposite — you lay the knife flat to remove the excess metal. You cannot just sharpen this little edge anymore; you have to get rid of metal, and on a double-sided knife you have to do both sides.

we basically have to lay this knife flat to remove any of the excess, excessive metal in here

14:00The re-grind

After thinning, the knife is significantly thinner than before. Re-establishing the bevel across the whole blade took a lot of work, but the result is clear: the knife cuts much better, and the bevel is straight and centred instead of sitting on one side.

16:47Watching the clad line

How do you know when to thin, and when to stop? Keep the edge and the cladding line the same distance apart — about five millimetres, give or take. Normal sharpening with the knife lifted is fine; once in a while, lay flat and remove the shoulder. That gap is the one to keep.

our goal is to always keep these two lines around the same distance, around the same distance

0:00How do you know when you're done with a stone?

People come to me all the time with a stroke count in their head — twenty on the 1000, thirty on the one above it — and that is exactly the mistake. Sharpening just removes old steel to expose fresh steel underneath, and the only signal that matters is the burr, or the wire edge, forming along the edge. Raise the burr in three strokes and keep going to thirty anyway and those extra twenty-seven do absolutely nothing for the edge.

3:53The fifty-stroke test

On this Naniwa Arata 1000 the burr came up after fifty strokes, and I stopped right there — stropped it, and took the edge to the microscope. For the second run I doubled it to a hundred strokes on the same knife so the two results could sit side by side, and a much wider wire edge appeared.

I'm able to form the burr in 50 times, 50 strokes, and let's go and have a look

5:19Once the burr is up, you're done

So what do the two results show? The same thing — after the burr has formed, extra strokes make no difference to how sharp the edge ends up. The danger with counting strokes actually runs the other way: if the burr needs fifty strokes and you stop at thirty, the burr never forms and you've wasted the session; push it out to a hundred and you've thrown away another fifty for exactly the same result.

after seeing the results, my conclusion is that both tests yield the same result

6:27When you can't feel the burr

This only really bites at the fine end: above about 3000 grit the burr becomes too fine to feel, and by 8000 you almost definitely can't feel anything at all. At that point it comes down to experience — once you've spent enough time on the stones you just know whether the burr is there or not. And it still has to come off: getting the burr off is every bit as important as raising it, and that's where the strop does its work.

0:00How is a badly damaged chef knife brought back to shape?

The knife in the video has lost its chef knife shape, so it gets a rough shaping first, removing the low damaged bit. Reprofiling is followed by major thinning, about 14 minutes in all, until the clad line is fully exposed and the blade is totally thinned down.

After reprofiling, we have to do major thinning around this lines. So we have to really thin it out.

1:18Does the knife get an edge after reprofiling?

The scratches left by thinning are refinished first, then the edge is put back through the 200 and 400 grit stages and up to 1,000. In the test at the end the knife cuts a potato instead of splitting it.

So we refinish the scratch a little bit, and then we give it an edge.

0:00Why does one spot on a knife edge wear out first?

The knife in the video shows typical uneven wear: a new knife curves up along the edge, and this one curves down in one area. The cause is using one spot of the blade heavily, sharpening only that dull spot each time, so over a longer period the area is sharpened over and over and the curve flattens out.

So what happen is, I just quickly sharpen this area and forget about the rest.

1:01How should the blade be sharpened to keep its performance?

When sharpening, the whole blade is sharpened according to the profile of the knife, not just one bit. The edge, the clad line and, on many knives, a distinct transition line run somewhat parallel; keeping all three going up together as the blade is sharpened keeps the performance of the knife.

So, first of all, when we are sharpening, we have to always sharpen according to the profile of the knife.