Hi, thanks for the replies! I've attached the best image I could get at this time using my phone. A bit hard to see, though.
(it can also be viewed here
It's really hard to tell if it's bare wood or sanding dust. Even after I looked at it under a loop, it was still tough to say. But it definitely might be sanding dust. After looking closely, it might be more in the grooves than on top, but not 100% so. It definitely does not come off with compressed air or wiping. And it wasn't there after the first top coat.
The poly top coat was most definitely dry. It had been put on almost 24 hours prior to the 2nd sanding, and it was over 80 degrees yesterday, so it was dry to touch within 30 min or so. And it had been put on 1.5 hours after the first coat (once lightly sanded), when it had been closer to 90 degrees out.
Wondering why it is showing so much on the top, but really nowhere else on the table?!? The only differences were that I sanded the top with the 400 sandpaper, and probably was a bit more aggressive than the rest of the table. And the poly on the top was laid on fairly heavy yesterday.
My carpenter is telling me that he thinks we can fix it by tinting the next top coat with black dye (he has some). He wants to do the whole thing so it would be uniform, I'm a bit nervous and would rather do just the top first to see what it does, since the rest of the table looks fine. I'm not convinced it will be enough, but he thinks it will.
He also tells me this wouldn't have happened if I would have used sanding sealer. I was under the impression that was optional and best for treating unfinished wood prior to top coating. Should I have used that? Remember that I specifically am going for the divits in the grain, as is fairly common for modern/contemporary furniture finishes.
Thanks for any help here!!!