  A small number of dusty Wolf-Rayet stars have been resolved into pinwheel
nebulae, defined by their ``rotating'' spiral dust shells observed in the
infrared. This morphology is naturally explained by dust formation associated
with colliding winds in a binary system. In order to confirm and further
explore this hypothesis, we have observed the known pinwheel nebulae (WR 104
and WR 98a) as well as the suspected binary WR 112 at multiple radio
wavelengths with the Very Large Array to search for non-thermal radio emission
from colliding winds. The spectrum of each target is nearly flat between 5 and
22 GHz, consistent with the presence of non-thermal emission that is reduced at
low frequencies by free-free absorption. This emission must lie outside the
radio ``photosphere,'' leading us to estimate a lower limit to the physical
size of the non-thermal emitting region that is larger than expected from
current theory. Based on a radio and infrared comparison to WR 104 and 98a, we
conclude that WR 112 is a likely candidate pinwheel nebula, but its temporal
variability indicates an eccentric binary orbit or a pinwheel viewed nearly
edge-on. A sensitive radio survey of IR-bright WRs would stringently test the
hypothesis that colliding winds lie at the heart of_all_ dusty WR systems. We
also discuss the effects of dust obscuration in the ultra-violet and how
radio-determined mass-loss rates of pinwheel nebulae (and dusty WR stars in
general) may be underestimated due to shadowing effects.
