  We review two procedures for constructing the vector potential of the
electromagnetic field on Kerr spacetime, namely, the classic method of Cohen &
Kegeles, yielding $A^\mu$ in a radiation gauge, and the newer method of Frolov
et al., yielding $A^\mu$ in Lorenz gauge. We demonstrate that the vector
potentials are related by straightforward gauge transformations, which we give
in closed form. We obtain a new result for a separable Hertz potential $H^{\mu
\nu}$ such that $A_{\text{lor}}^\mu = \nabla_\nu H^{\mu \nu}$.
