The Collaborative International Dictionary of English v.0.48:

Shrinking \Shrink"ing\,
   a. & n. from Shrink.
   [1913 Webster]

   Shrinking head (Founding), a body of molten metal connected
      with a mold for the purpose of supplying metal to
      compensate for the shrinkage of the casting; -- called
      also sinking head, and riser.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sinking \Sink"ing\,
   a. & n. from Sink.
   [1913 Webster]

   Sinking fund. See under Fund.

   Sinking head (Founding), a riser from which the mold is fed
      as the casting shrinks. See Riser, n., 4.

   Sinking pump, a pump which can be lowered in a well or a
      mine shaft as the level of the water sinks.
      [1913 Webster]