Originally Posted by Andy M.
Zagat, I do believe you've jinxed me!
Seems like talking about it wasn't the trick.
I'll agree with medtran. The seam appears to have the same black. The smudge appears in the middle of the board but your problem could be coming from the seams. I doubt it's coming through the hardwood and finish.
Does it wipe off easily?
What do you wash the floor with?
Kinda/Sorta looks like mold that the spores could be spread during a damp mop.
Notice how the black is in the crevices of the grain.
If it wipes off it's on the surface on top of the finish.
If it is a mold I can only suggest using a little bleach in your wash water and keeping things as dry as you can for while.
Or perhaps refinishing the floor to help seal up the joints where moisture can penetrate.
Best of luck and keep us informed of what you find out about Casper.