Part of the slurry dried out on a Shapton Kuromaku 1k, and it changed the stone.

[Knife2meatu]

I was doing significant grinding on the sides of a stainless knife with coarse stones and decided to compare the Shapton Kuromaku 1k to the Chosera 800 by removing the coarse scratches with one stone per side.

After working up a good amount of dark metal slurry on the Shapton, I put it aside while I did the same on the other side with the Chosera. By the time I was done with the second stone, the slurry on the Shapton had partially dried -- or dried out enough that it lightened noticeably in color in one area of the stone. I tried just spraying a little water to get the slurry wet again but something was feeling off compared to before.

So I completely rinsed the entire surface at this point. To my surprise, the area where the slurry had dried out didn't look the same as the rest of the stone when the surface was rinsed: it is slightly discolored, darkened; it also now absorbs water more readily than the rest of the stone and seems softer; I think the feedback may be slightly increased as a result. Also, the discolored spot now takes longer to dry after use, presumably as a result of the extra water absorption.

This happened a few weeks ago, and tonight was my second or third time using the stone in as many weeks, so I'm sure it had time to dry out in the meantime. Furthermore, I lapped the stone when it happened; lapping until the entire surface had been refreshed, but stopping short of trying to lap until the discoloration was gone because it appears to have affected the stone deep enough that I don't want to lap away what is an already pretty thin 15mm stone.

Anybody have this experience with a Shapton Pro/Kuromaku?

 

[Ivan Hersh]

I am just guessing your stone has just absorbed, some small amounts of steel in this part of the stone.

 

[Dave Martell]

Was the knife clean before you started sharpening, all oil removed? I ask because I've had two stones get oil dripped on them (both Shapton Pros) and what you described is exactly what happened to them.

 

[Knife2meatu]

Was the knife clean before you started sharpening, all oil removed? [...]

I do not think there was oil on the knife, but you've got me wondering. On one hand, I'm sure I did clean the blade with strong dish soap before; but on the other hand, the immediately preceding stones were used with oil. And it isn't obvious to me that scrubbing with water and soap removes oil completely, particularly from inside the scratches.

However, the way it happened doesn't suggest to me that it is oil contamination -- thinking back: I work up a lot of black mud on the surface; set it aside with this wet mud and when I pick it up again, roughly a third of the surface has had time to dry out; I spray a little water all over, and although the still wet mud is immediately slick and workable, the dried part feels stuck on and isn't coming loose with just light finger rubbing; so I rinse the surface, and observe a darkening of the stone under the area where the mud dried enough to lighten in color -- the shape of the discolored stone follows the shape of the dried mud exactly.

I'm trying to think how this could be due to oil from the previous stone, supposing the cleaning didn't get it all, but I'm skeptical that's it. On most other stones, I guess this would just be considered loading and there would be little to make of it -- for instance, the Cerax 1k & Bester 1200, white stones the both of them, darken noticeably with usage and I would have to lap the surface to restore pristine color -- but the Shapton 1k usually resists this kind of discoloration comparatively well. Were it not for the Shapton usually rinsing off clean and this only happening where the mud had time to dry out, this wouldn't be too remarkable.

However, the way this area of the stone now behaves differently than the rest of the stone is pretty intriguing. It not only absorbs water slightly differently, but now loads up faster than the rest of the stone, also: sharpening now leaves noticeably darker marks across this section of stone. If I lightly rub steel against the entire surface, like rubbing a pencil lightly across a sheet of paper to reveal hidden indentations, this part of the stone stands out on account of it darkening comparatively faster than the rest.