The tool here is called a Bending Fork or Scroll Fork.
It is a very useful tool in the making of scrolls for brackets, grates, rails, fences, etc
I made the tool from a flat rectangular piece of rail road tie plate.
The material has quite a high carbon percentage from what I can tell from past experiences, so the tool was tempered to a dark blue colour.
In the lower pictures depict how the tool is used.

Both the watercolour and the photograph is from a book titled "Werk und Werkzeug des Kunstschmieds" by Otto Schmirler.