The reason the edge looks like that is because it happens during the blanking process. Thethickness of the clad layer is the same on both sides of the copper, but as the blanking punches go down through the strip it "smears" the layers at the edge. It is easier to uderstand if you consider what the inside of the hole in the strip would look like. As the punch goes through the strip it smears the top surface layer down over the copper and the copper layer down over the bottom layer. So if uou look at the edge of the hole you will see thick, thick, thin or non-existent. On the blank the layers smear in the opposite direction so if you were able to keep the top and bottom layer orientation the same, the edge of the blank would be thin or non-existent, thick, thick. (This is also useful in confirming "clipped" planchet errors. Since the edge of the coin is the edge of a blank, and the edge of the clipped portion is the edge of a hole, the layering thicknesses will will be reversed between the edge of the coin and the edge of the clip.)