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I am new to using whetstones. As such, I purchased a cheap Whetstone (manufacturer is FULUDM) and used an old cheap knife to practice.

What I've noticed is, the 1000g grit (which is a green stone) seems to generate a paint like substance. My searches online provide 0 results as to what this is.

Is this expected or does this indicate a fault or a poor technique?

My technique? Soak it for 30 minutes and ensure there is a thin layer of water on the top at all times (as per the instructions). Hold the knife at about 22 degree angle (depending on material).

You can see the state of my knife from the Whetstone enter image description here

And this gif should also show the paint like substance generated (sorry it's so low quality)

enter image description here

enter image description here

MyDaftQuestions
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2 Answers2

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This is perfectly normal.

Both faces 'suffer' from the physical action of rubbing them together, as you sharpen the knife you abrade the surface of the whetstone too.
As the grit is very fine, it forms a paste, which just needs rinsing off after you've finished.

Eventually, you'll wear a hollow where the knife has worn away the stone, just like footfall on an old stairway.

enter image description here

Tetsujin
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    I suspect this "cheap" whetstone will dish out a lot faster than a more-expensive one. But an expensive one that lasts twice as long while costing 5x as much, not exactly a bargain. – Criggie Mar 27 '23 at 01:41
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    You can always un-dish the stone... – arne Mar 27 '23 at 07:07
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    If purchased as a set, there should be an extra plate or stone for re-flattening the stones. This needs to be done to keep sharpening effective. – Jack Aidley Mar 27 '23 at 07:30
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    @JackAidley often not with cheap ones, but they're so cheap that if you use them enough that they dish, you can buy a 2nd stone for flattening – Chris H Mar 27 '23 at 10:40
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    I believe the paste that builds on the stone is called slurry, and it is very important to the process of honing. Don’t rinse it off. – Philipp Mar 27 '23 at 11:26
  • @Philipp - I clarified my original intent by adding 'afterwards'. tbh my stone never used to shed anywhere near as much as the OP's [a Global, pretty expensive] so the point was almost moot. I've since moved to an electric sharpener, so I no longer have to contend with the issue at all. It was a task I was very poor at. ;) – Tetsujin Mar 27 '23 at 12:39
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    Phillip is correct. I've added an answer which explains this. The slurry isn't a byproduct; it's the sharpening mechanism. That's aside from this specific stone maybe being trash. – FuzzyChef Mar 27 '23 at 17:07
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    @Philipp It's called /a/ slurry, and (considered from an engineering POV) it might or might not be desirable. If it is being caused by the binder in the stone failing before there is any significant abrasion to the knife, then it's undesirable: the stone's useless. OTOH, high-quality engineering grindstones have friable grit that cracks during use to expose new sharp edges, it's those sharp edges which have a cutting effect on even hard materials, and it's routine to "re-flat" the stone (using a harder stone or a diamond) on a regular basis. – Mark Morgan Lloyd Mar 28 '23 at 07:04
  • Mark: this is not an engineering grindstone, though, it's a knife sharpening stone. – FuzzyChef Mar 28 '23 at 16:24
  • @Tetsujin Sorry if my comment might have sounded rude. I own three Japanese stone (Naniwa Superstone series). They need to be activated with a nagura stone prior to honing the knives. I have not worked with other stones, but maybe there are stones that don’t require a slurry at all, in which case my comment would be incorrect. Also, I have only sharpened straight razors, not kitchen knives, although the process should be similar up to a certain point. – Philipp Mar 28 '23 at 17:36
  • @Philipp - no worries; I'm not too precious about my slurries or lack thereof ;)) tbh, I spent years with a stone which made some, but relatively little slurry. I never managed to get the damn knives properly sharp, so I gave up & bought an expensive electrical one instead. My slurry & sharpening worries are long over :) See https://cooking.stackexchange.com/a/108740/42066 for my 'journey'. – Tetsujin Mar 28 '23 at 17:42
  • Whilst you have helped me sooo many times in the past, I think the other answer is better for me as it calls out the importance of the paste remaining and being part of the process where as you suggest it needs to be rubbed off. Googling suggests the other answer is correct _despite_ the number of upvotes – MyDaftQuestions Apr 02 '23 at 17:20
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That slurry of grit is actually part of how that kind of whetstone works. It's not only normal, but necessary for it to sharpen properly. On "natural"-style fine sharpening stones, the idea is that you are sharpening the knife using a grit slurry rather than on the solid stone itself. This allows for finer sharpening and polishing than you could get from a stone that does not slurry.

In fact, with this style of sharpening stone, you generally rub the stone hard before even touching a knife to it(video) in order to create a slurry.

I have a two-sided King Japanese sharpening stone, which works like this and is how I sharpen my hand-forged knives. The stone you bought looks like a generic knockoff of a King. How well it actually works is up to you to determine; I will say that seems to be creating a lot more slurry than I'm used to.

FuzzyChef
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  • The Japanese even have separate little [nagura stones](https://toolsforworkingwood.com/store/blog/91/) for the purpose of creating a slurry. And there are quality stones of varying hardness; it mostly depends on technique and style which kind suits you better. – phipsgabler Mar 28 '23 at 08:22