A rapid, sensitive technique has been developed for the determination of small concentrations (about 1 microgram/cm. 2) of finely divided inorganic solids on a variety of planar substrates. The technique has been applied to a study of the removal of such inorganic deposits by flowing or agitated aqueous phases. Many of the observations have parallels in well-known colloidal phenomena. Some unusual “aging” effects are described and possible explanations for this unexpected behavior are offered.