  Renormalization group and Coulomb gas mappings are used to derive theoretical
predictions for the corrections to the exactly known asymptotic fractal masses
of the hull, external perimeter, singly connected bonds and total mass of the
Fortuin-Kasteleyn clusters for two-dimensional $q$-state Potts models at
criticality. For q=4 these include exact logarithmic (as well as loglog)
corrections.
