Modeling the etching of pre-heated silica NPs is not feasible because we do not know the NP composition as a function of depth below the surface. We can say that initially, just after preheating, the NPs must have Si-rich surface layers that etch similarly to Si NPs, but the etching chemistry gives no direct information about whether the NP subsurface retains substantial oxygen content (i.e., a silica core), and how large such a O-rich core might be. There are, however, several observations that put constraints on the composition/structure of the NPs as produced by preheating, and after passivation. As discussed above, the high 532 nm absorptivity and visible/near IR emissivity of the pre-heated silica NPs implies that they must have a substantial volume of Sirich material, and while the initial etching kinetics imply that the surface layer must be Si-rich, the optical properties, which are not dissimilar to those of Si NPs, suggest that there much be substantial Si-rich material in the subsurface. Furthermore, the fact that the NPs retained their 532 nm absorptivity and visible/near IR emissivity after passivation implies that the passivated NPs still had a substantial volume of Si-rich material. This residual Si-rich material could have been a