  We observe powder ''droplets'' forming when tapping repeatidly an horizontal
flat plate initially covered with a monolayer of fine powder particles.
Starting from a simple model involving both the air flow through the porous
cake and avalanche properties, we setup an analytical model which
satisfactorily fits the experimental results. We observe a close analogy
between the governing equations of the phenomenon and the basic physics of
wetting liquids, including the equivalent of the Laplace-Young law and the
surface tension parameter leading to the familiar Rayleigh Taylor instability.
