  Grease, as used for lubrication of rolling bearings, is a two-phase organogel
that slowly releases oil from its gelator matrix. Because the rate of release
determines the operation time of the bearing, we study this release process by
measuring the amount of extracted oil as a function of time, while we use
absorbing paper, to speed up the process. The oil concentration in the
resulting stain is determined by measuring the attenuation of light transmitted
through the paper, using a modified Lambert-Beer law. For grease the timescale
for paper imbibition is typically 2 orders of magnitude larger than for a bare
drop of the same base oil. This difference results from the high affinity, \it
i.e. wetting energy per unit volume, of the oil for the grease matrix. To
quantify this affinity, we developed a Washburn-like model describing the oil
flow from the porous grease into the paper pores. The stain radius versus time
curves for greases at various levels of oil content collapse onto a single
master curve, which allows us to extract a characteristic spreading time and
the corresponding oil-matrix affinity. Lowering the oil content results in a
small increase of the oil-matrix affinity yet in a significant change in the
spreading timescale. Even an affinity increase by a few per mill doubles the
timescale.
