I was wondering if the frame back razor had a spocific reason for its design?
Framebacks can be made sharper because they can use a steel for the blade that would not be appropriate for the frame. Something harder but more breakable.
fontenille made a frameback in Damascus steel that is truly hard to beat. The lecoultre is another great example.
My understanding is that this is the case for earlier Japanese stuff. Swedish steel for the edge and crap local steel for the rest.There is one school of thought that says they were a cheaper way to manufacture razors, using the "good" steel just for the blade and lesser quality for the, "frame"