  We present high-resolution infrared (2--18 micron) images of the archetypal
periodic dust-making Wolf-Rayet binary system WR140 (HD 193793) taken between
2001 and 2005, and multi-colour (J -- [19.5]) photometry observed between 1989
and 2001. The images resolve the dust cloud formed by WR140 in 2001, allowing
us to track its expansion and cooling, while the photometry allows tracking the
average temperature and total mass of the dust. The combination of the two
datasets constrains the optical properties of the dust. The most persistent
dust features, two concentrations at the ends of a `bar' of emission to the
south of the star, were observed to move with constant proper motions of
324+/-8 and 243+/-7 mas/y. Longer wavelength (4.68-micron and 12.5-micron)
images shows dust emission from the corresponding features from the previous
(1993) periastron passage and dust-formation episode. A third persistent dust
concentration to the east of the binary (the `arm') was found to have a proper
motion ~ 320 mas/y. Extrapolation of the motions of the concentrations back to
the binary suggests that the eastern `arm' began expansion 4--5 months earlier
than those in the southern `bar', consistent with the projected rotation of the
binary axis and wind-collision region (WCR) on the sky. Comparison of model
dust images and the observations constrain the intervals when the WCR was
producing sufficiently compressed wind for dust nucleation in the WCR, and
suggests that the distribution of this material was not uniform about the axis
of the WCR, but more abundant in the following edge in the orbital plane.
