  We suggest that when zinc is substituted for copper in the copper oxide
planes of high $T_{c}$ superconductors, it does not necessarily have a valency
of 2+. Rather, the valency of a zinc impurity should be determined by its
surrounding medium. In order to study this hypothesis, we examine the effect of
static impurities inducing diagonal disorder within a one band Hubbard model
coupled to a localised state. We use this model to discuss the physics of zinc
doping in the cuprates. Specifically, we discuss the formation of local moments
near impurity sites and the modification of the transverse spin susceptibility
in the antiferromagnetic state.
