The phenomenological theory of Wiseman and Feaster, based on the two-charge theory of Gross, expresses the polarization response of an absorptive dielectric as the superposition of responses to changes in the internal field, using a time-dependent specific polarization function. This theory is extended to explain quantitatively the charge decay of unshielded dielectrics of finite resistivity. From measurements of the net surface charge on unshielded Carnauba wax electrets at 40°C and 10−5 Torr, it is concluded on the basis of this theory: (i) that the internal field is the main decay agent, governing both polarization growth and real surface decay, which together account for the decay of the net surface charge; (ii) that there is no net local charge within the volume of the dielectric; (iii) that the volume resistivity is 9.0±0.5×1017 Ω-cm, and the dielectric constant at a frequency of the order of 1 cps is 3.08±0.12.