Nakayama ??? Kan Asagi

I have used this stone many times but I put it away for a while and recently got it back out to use. I lapped it and used it and everything was fine, just as normal. I put it up and when I took it back out I noticed it had these spots on it. They dont effect honing and I cant feel them on the surface but it just looks strange. Within these light spots there are little black specks. I lapped it good one more time to make sure it wasnt something I had spilt on the surface and they are still there. Seems strange to me. After further inspection, I noticed that on the sides on the stone there are streaks of these really fine black dots also so I am guessing it is a natural formation. The black specks I can see on the sides are not surrounded by lighter spots of stone tho. Seems a little strange that they would just appear like that when there was no sign of them before. Maybe somebody can tell me what this is. I have pictures of the stone before in the BST section. On a side note, it appears that all but one of the sides of this stone were sanded. I can see a few places where the saw marks didnt get wiped out. Was this common Practice at one time and does this help determine the period the stone was mined? I went ahead and took a picture of the back too

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You never know what is in the stone. With use and lapping one can reveal hidden defects, or karasu/nashiji/goma.
I have seen stones that had the sides lapped, I think those are newer production stones, older production stones would have huge saw marks.

It has saw marks on the sides they were just sanded down on all but one of the ends. You can still see a few of the deeper saw marks on the sanded sides. I have taken pictures of the end not sanded and the two long sides that were sanded. I thought I had read somewhere that they sanded the sides of stones many years ago, not recently. I am not sure of this tho.

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On the first photo, the saw marks look like they were made from a cutting machine (disc?), not by hand. It could be possible that it was recently cut from a bigger piece.

what did you lap the stone with? Is it possible that there was someting on the plate/paper that could have been deposited into/onto the stone that is causing the white spots?

I have a shapton 1k that I use for final lapping. Every so often I check it for flatness too but it hardly ever needs any work. It appears like something dripped on the stone and made the marks but they are still there after relapping. It hasnt effected the performance YET so maybe I should just not worry about it.

could just be some kind of salt coming out of whatever the black dots - goma - are I suppose. Water deposits are funny - sometimes they take forever to get rid of them - I had a synth that purged some kind of white after soaking once... it finally lapped out but it kind of freaked me out. I never could tell if it came out of the stone or the water I was soaking it in.