  We explore the viscosities of a photon gas by means of the Euler-Heisenberg
effective theory and quantum electrodynamics at zero electron chemical
potential. We find parametric estimates that show a very large shear viscosity
and an extremely small bulk viscosity (reflecting the very weak coupling
simultaneously with a very approximate dilatation invariance). The system is of
some interest because it exemplifies very neatly the influence of the breaking
of scale invariance on the bulk viscosity.
