to be on the anvil

from The Collaborative International Dictionary of English v.0.48

Anvil \An"vil\, n. [OE. anvelt, anfelt, anefelt, AS. anfilt,
   onfilt; of uncertain origin; cf. OHG. anafalz, D. aanbeld.]
   1. An iron block, usually with a steel face, upon which
      metals are hammered and shaped.
      [1913 Webster]

   2. Anything resembling an anvil in shape or use. Specifically
      (Anat.), the incus. See {Incus}.
      [1913 Webster]

   {To be on the anvil}, to be in a state of discussion,
      formation, or preparation, as when a scheme or measure is
      forming, but not matured. --Swift.
      [1913 Webster]