  Spin networks appear in a number of areas, for instance in lattice gauge
theories and in quantum gravity. They describe the contraction of intertwiners
according to the underlying network. We show that a certain generating function
of intertwiner contractions leads to the partition function of the 2d Ising
model. This implies that the intertwiner model possesses a second order phase
transition, thus leading to a continuum limit with propagating degrees of
freedom.
