The customer who took this picture thought that the dark spots in the corners were due to mold; however, they appeared within just days after the finish was applied. We were able to obtain a small section of the discolored wood and just looking at it gives the impression that the discolorations could well be mold, or some flecks of dirt that may have been present at the time of staining. Even under the microscope at 10X magnification, there’s no indication of what caused the black spots.

But at 60X magnification it quickly becomes apparent that every black spot is associated with some type of fiber imbedded in the film. These fibers are bits of steel wool. Since the black spots are concentrated in the corners, it’s evident that someone had tried to wipe the wall clean but missed the corners entirely.