From your photo, it looks like the right side corner along the length of the stone is high. rounding it will prevent your sharpening efforts from being focused on that part of the stone and allow it to be istributed over a larger area.
Nothing out of the ordinary with that picture
The Rika, more than any of my other stones, tends to get clogged/loaded. Yours looks normal for a few minutes of use, I wouldn't worry about it. But after heavier use you may notice that it starts to feel scratchy. I'm OCD about mine and flatten/clean between every knife with a diamond plate. I don't even like to flatten my other stones, just wear 'em out with normal use, but the Rika feels much better when it's clean. My two cents. I also find the longer it is in water, the better.
Agreed the rika feels buttery smooth when clean but I find I have to flatten it beyween every use. Not so much to flatten but to take clogged swarf out of it. I've started perma-soaking mine and have noticed improvement.
All normal people love meat. If I went to a barbeque and there was no meat, I would say 'Yo Goober! Where's the meat?'.- Homer Simpson
I've found that the longer Rikas soak, the better they work. Flatten it, chamfer the edges, soak it overnight, and you might be pleasantly surprised. You'll probably still get some of those black streaks, but it will feel great and work great.
I just hold it under running water and scrub it with my fingers or a paper towel and most of the clogging comes off. At least it does for me.
"Sucking at something is the first step to becoming sorta good at something." -Jake the Dog
Beveling the edges helps keeping them from chipping + you never want high edges on a stone.Also get a small spray bottle to mist the stone while sharpening,works well to loosen mud.
Sounds like you have some good stones & quality knife too.
Listen to the sound the stone makes when you are sharpening. I feel it when it starts to get clogged and swear it sounds different (less gritty?).
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