  Electromagnetism in spacetime can be treated in terms of an analogue linear
dielectric medium. In this paper, we discuss the gravitational analogue of the
linear magnetoelectric effect, which can be found in multiferroic materials.
While this is known to occur for metrics with non-zero mixed components, we
show how it depends on the choice of spatial formalism for the electromagnetic
fields, including in differences in tensor weight, and also on the choice of
coordinate chart. This is illustrated for Langevin-Minkowski, four charts of
Schwarzschild spacetime, and two charts of pp gravitational waves.
