We present a series of benchmark measurements of the ionization balance of well-characterized gold plasmas with and without external radiation fields at electron densities near 10{21} cm{-3} and electron temperatures spanning the range 0.8 to 2.4 keV. We have analyzed time- and space-resolved M-shell gold emission spectra using a sophisticated collisional-radiative model with hybrid level structure, finding average ion charges Z ranging from 42 to 50. At the lower temperatures, the spectra exhibit significant sensitivity to external radiation fields and include emission features from complex N-shell ions. The measured spectra and inferred Z provide a stringent test for non-local-thermodynamic-equilibrium models of complex high-Z ions.