Not too knowledgeable about axes, please don't beat me up
Was experimenting with a 2 lbs or so small hatchet (Øyo, Norwegian make) and refining its edge and this line developed as I reached the finer grits, more or less equally on both sides of the edge. I don't think its caused my abrasives. Is it really the separation between hardened and softer backing steel, or some other phenomenon?
Mac

Was experimenting with a 2 lbs or so small hatchet (Øyo, Norwegian make) and refining its edge and this line developed as I reached the finer grits, more or less equally on both sides of the edge. I don't think its caused my abrasives. Is it really the separation between hardened and softer backing steel, or some other phenomenon?

Mac