The amount of marking caused by a caning depended on both the size and thickness of the cane, add to of course the clothing worn and the force with which it was applied.
From my experience, heads who caned over trousers and pants tendee to leave a boys bottom marked much longer than those that did it on just pants or bare. On trousers a much thicker cane was used. This in fact tended to numb the buttocks after about three strokes. After three strokes it just marked the bottom causing extensive bruising. The pain was not felt until the feeling started to return to the buttocks. Heavt canes did not bend on impact so the full impact was on the bottom. This caused massive bruising and in many cases cut and grazed the bottom.