This phrase occurs to me from time to time. I heard it used by a demonstrator at a conference. Unfortunately I can’t recall that person who said blacksmithing tools generally fall into two categories, the very sharp and the very dull. I also recall a blacksmith who emphasized the importance of keeping punches sharp. These phrases usually come back to me when I’m dressing a tool face or making a new tool or perhaps relieving the edges on a die.
It is pretty obvious that cutting becomes fullering at some ambiguously fine line. Hammers, too, are essentially fullers until the face radius is zero in which case they become flatters.
Neither dull cutting edges or sharp fullering edges are very useful. What ever the working surface radius it seems to work best when highly polished. That is where the progressive smoothing from coarse wheel grinding to belt sanding to silicon carbide wheel preliminary polishing to hard felt wheel and buffing compound finish polishing is important. The highly polished surface seems desirable no matter whether it’s a face tool or and edge tool.
The forging atmosphere is a corrosive one. I can easily see that the rust forms on steel surfaces fastest in the forge room. Every spring die which was once polished is today rusty because it has been affected by the humidity and the chemicals in the coal smoke. It’s just not practical to keep all the tool faces mirror bright so it’s always a matter of thinking through the work process and deciding what is “good enough.”