In spite of the nice figure, the wood seems to have fairly large pores. It appears that your finish may be "dry" between coats, but not fully cured, which can take weeks with some finishes... especially if there is raw linseed oil in the finish. Then you risk having rottenstone powder getting embedded in the incompletely cured finish in some areas.
At this point, it may be best to use mineral spirits to wipe the stock down to remove the finish that has embedded rottenstone, since those areas may appear slightly more translucent than places where it is not embedded.
Then going forward, add a bit of Japan dryer to the finish, and give it more time to cure between coats, especially if you will be using rottenstone or pumice. Personally, I've never used either rottenstone or pumice between coats. Only after the final coat, if necessary.
