Published online by Cambridge University Press: 26 May 2016
Dust formation by Wolf-Rayet stars is a powerful diagnostic of exceptional activity in their winds. Observed behaviour ranges from stars which make dust continually (e.g., WR 104, WC9d+B0.5V) to those which make dust for short episodes at periodic intervals (e.g., WR 140, WC7pd+04-5). In both examples, dust formation is related to colliding WR and OB stellar winds in binary orbits. We have been using IR photometry primarily from the SAAO and ESO and spectroscopy with ISO-sws to investigate systems having intermediate properties (WR 98a, WC8-9vd+?) or more complex behaviour (WR 48a, WC8ed+?).