  Recently, it was realised that liquid viscosity has a lower bound which is
nearly constant for all liquids and is governed by fundamental physical
constants. This was supported by experimental data in noble and molecular
liquids. Here, we perform large-scale molecular dynamics simulations to
ascertain this bound in two other important liquid types: the ionic molten salt
system LiF and metallic Pb. We find that these ionic and metallic systems
similarly have lower viscosity bounds corresponding to the minimum of kinematic
viscosity of about 10$^{-7}$ $\frac{{\rm m}^2}{\rm s}$. We show that this
agrees with experimental data in other systems with different structures and
bonding types, including noble, molecular, metallic and covalent liquids. This
expands the universality of viscosity bounds into the main system types known.
