I suspect it was seen than - as now, as a way of trying to get that infinitesimal extra from a blade that doesn't really need it.
Many years ago men would try much the same thing with a used blade on a window pane, trying to extend the life of a blade that was gone. That was different of course, because it would still tug regardless.
Many years ago men would try much the same thing with a used blade on a window pane, trying to extend the life of a blade that was gone. That was different of course, because it would still tug regardless.