  Formation and dynamics of an Al(OH)_3 precipitation ring is studied by
diffusing NaOH into a gel containing AlCl_3. Limited feeding of the outer
electrolyte (NaOH) is found to yield an intricate ring-dynamics which involves
stopping and reversal of the direction of motion of the precipitation ring, and
evolution into stationary multi-ring structures. A model of the ring-dynamics
is developed by combining a phase separation scenario for the precipitation
with the redissolution (complex formation) of the precipitate in the excess of
the outer electrolyte.
