We present new infrared photometry of the WC7-type Wolf-Rayet star HD 19264
1 (WR 137) from 1985 to 1999, These data track the cooling of the dust clou
d formed in the 1982-84 dust-formation episode from 1985 to 1991, the incre
ase of the infrared flux from 1994.5 to a new dust-formation maximum in 199
7 and its subsequent fading, From these and earlier data we derive a period
of 4765 +/- 50d (13.05 +/- 0.15 yr) for the dust-formation episodes. Betwe
en dust-emission episodes, the infrared spectral energy distribution has th
e form of a power law lambdaF(lambda proportional to) lambda (-1.86) . The
rising branch of the infrared light curve (1994-97) differs in form from th
at of the episodic dust-maker WR 125, Time-dependent modelling shows that t
his difference can be attributed to a different time dependence of dust for
mation in WR 137, which occurred approximately proportional tot(2) until ma
ximum, whereas that of WR 125 could be described by a step function, akin t
o a threshold effect. For an adopted distance of 1.6 kpc, the rate of dust
formation was found to be 5.0 x 10(-8) M-circle dot yr(-1) at maximum, acco
unting for a fraction f(c) approximate to 1.5 x 10(-3) of the carbon flowin
g in the stellar wind. The fading branches of the light curves show evidenc
e for secondary 'mini-eruptions' in 1987, 1988 and 1990, behaviour very dif
ferent from that of the prototypical episodic dust-maker HD 193793 (`WR 140
), and suggesting the presence in the WR 137 stellar wind of large-scale st
ructures that are crossed by the wind-wind collision region.