  We compute the exact partition function of the isotropic 6-vertex model on a
cylinder geometry with free boundary conditions, for lattices of intermediate
size, using Bethe ansatz and algebraic geometry. We perform the computations in
both the open and closed channels. We also consider the partial thermodynamic
limits, whereby in the open (closed) channel, the open (closed) direction is
kept small while the other direction becomes large. We compute the zeros of the
partition function in the two partial thermodynamic limits, and compare with
the condensation curves.
