Why is my sharpening stone producing a lot of dust/paste or crumbling?

Question

I got this sharpening stone and soaked it in water for an hour before using it on some fairly dull pocket knives. I have never sharpened a knife like this before, and only have watched a bunch of Youtube videos to learn how.

I've got my blade somewhere around a 15~20 degree angle as far as I can tell, and am applying approx 8lbs of pressure, mostly when pulling back (and just relax when moving the knife forward across the stone). In the videos the stone just sort of sits there and maybe a fine grey/silver/metal grit/dust starts to appear on the stone's surface. This is not what is happening for me. The blade of the knife is quickly accumulating a large amount of, very wet, stone dust build-up on it (the surface of the stone is also accumulating this dust/paste). I don't see this happening in any of the videos online and don't see anyone talking about this anywhere... I sharpened for maybe 30 minutes and the knife was... kind of sharp, but definitely not razor sharp. I feel like perhaps this dust is a symptom of something I'm doing wrong.

Here's the knife I'm trying to sharpen:

Answer 1

This knife needs either a different angle for sharpening or you'll have to grind the ridge right at the sharp edge away. Also, you have a rather coarse grinding stone.

The cross-section of the blade looks something like this: (over exaggerated)

I'm no expert in knife making, but I think it's formed this way to keep the edge sharp for longer and make it resilient against nicks. If you grind at a 20° angle, you only grind the ridge down, but the actual cutting edge is not affected.

You should practice blade sharpening on an old kitchen knife that has a triangular cross section. Like this:

The coarse side (labeled "400" on your stone) is to grind the blade down to the right angle and to remove big nicks. Looking at the blade under a magnifier after grinding, you'll see many fine scratches along the direction you ground. The fine side (labeled "1000" on your stone) is to remove small nicks and scratches (from coarse grinding) on the blade. To actually polish the blade to razor sharpness you'll need a much finer grinding stone. The standard for finer stones seems to be 3000 and 8000 grit.

The finer your stone, the less stone dust I would expect. Since 400 is very coarse for a grinding stone, I'm not surprised you see a lot of stone dust while grinding the ridged blade. The ridge knocks the fine sand particles the stone is comprised of loose. You should see less stone dust when sharpening a blade with a triangular cross-section and when using less force, but the grinding will take longer.

Answer 2

I do not have experience with the product you are using (I mean, the stone). For kitchen knives, I use a much coarser stone, with a satisfying level of success. I never noticed any of the wet dust problem you mention. I also get the job done in under one minute (no perfection required in my case, just the good ability to cut).

So my 2 cents would be along the lines of:

• it is normal for that wet dust to be there (unlikely IMO);

or

• you have an under-quality product. Maybe a scam, maybe just an unlucky failure.

You can give it a try with another (kind of) stone, and compare the results.

Answer 3

To me this sounds like either the stone is of poorer quality or it has been over-soaked prior to use. Given the build up of residue, there are a few things you could try. A shorter soak time would be the obvious choice.

What I would probably do here is give the stone a very brief soak then actually sharpen the knife with the stone immersed under a couple of inches of water. Any residue should then not build up but dissipate into the water. After sharpening with the 400 and 1000 grit, I would then dry the knife and finally sharpen using a sharpening steel to finish the honing.