  The screening of plate-plate interactions by counterions is an age-old
problem. We revisit this classic question when counterions exhibit a
distribution of charges. While it is expected that the long-distance regime of
interactions is universal, the behaviour of the inter-plate pressure at smaller
distances should a priori depend rather severely on the nature of the ionic
mixture screening the plate charges. We show that is not the case, and that for
comparable Coulombic couplings, different systems exhibit a quasi-universal
equation of state.
