I am working with wood from a locust tree that has been dead for the past few years (I live in central Illinois). After it was cut down, I cut several cross cut "disks," perpendicularly cut across the length of the logs in different parts of the tree in order to try to make end tables.

Each disk is 1 to 3 inches thick and has a width/circumference that was dependent on the placement of the cut (tree truck discs were about 20 inches in diameter, others only 5 to 6 inches diameter). I am sanding the surfaces down and revealing a really nice grain, but some of the discs have a natural split in the middle. This is not a crack or split from drying, but is a split from the natural growth of the tree. A simple crack from drying can be fixed by a simple youtube search and there are multiple methods, but this one is a little different.

Without enlarging the crack to sand/clean out the black "dirt,, what is a good method for filling this gap so I can coat in shellac and complete my end table? Yes, the gap goes through the entire disc, and can be seen from both the top and bottom. I attached two images of my cross cut disks and below is a link to what my final product will look like. The link is only for a visual perspective of what I am going for if any of this didn't make sense. (Note: image missing.)