White dwarfs, stellar embers depleted of nuclear energy sources, are condemned to cool down for billions of years. As this cooling can be modeled, the age of a white dwarf can be determined from its temperature, mass and chemical composition. The coolest - and thus oldest - white dwarfs can therefore be used to place constraints on the age of the components of the Milky Way. However, until recently, the atmosphere models of cool helium-rich white dwarfs were inappropriate for the fluid-like densities encountered at the photosphere of those objects, implying that the calculated ages were incorrect. Using modern ab initio calculations, we have developed a new generation of atmosphere models that include an accurate description of the constitutive physics. We have focused our efforts on cool metal-polluted white dwarfs, which offer more opportunities for comparisons between models and observations than pure helium atmospheres. We have demonstrated that our new models satisfactorily reproduce the observed spectra of the most peculiar cool white dwarfs. Once validated, this new code has enabled us to precisely map the chemical evolution of cool white dwarfs, showing among other things that accretion of hydrogen from the interstellar medium does not play an important role in the evolution of those objects. (LA-UR-19-29924)