  We are investigating the formation and evolution of dust around the
hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim
to determine the connection between the probable merger past of these stars and
their current dust-production activities. We carried out high-angular
resolution interferometric observations of three RCB stars, namely RY Sgr, V
CrA, and V854 Cen with the mid-IR interferometer, MIDI on the VLTI, using two
telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the
dusty environment at very small spatial scales (~ 50 mas or 400 stellar radii).
The observations of the RCB star dust environments were interpreted using both
geometrical models and one-dimensional radiative transfer codes. From our
analysis we find that asymmetric circumstellar material is apparent in RY Sgr,
may also exist in V CrA, and is possible for V854 Cen. Overall, we find that
our observations are consistent with dust forming in clumps ejected randomly
around the RCB star so that over time they create a spherically symmetric
distribution of dust. However, we conclude that the determination of whether
there is a preferred plane of dust ejection must wait until a time series of
observations are obtained.
