The surface tension components and parameters for nine naturally occurring colloidal-sized volcanic ash samples were determined by thin-layer wicking. These materials include rhyolites, trachytes, phonolites, and an andesite, and were collected from deposits in California, Arizona, Italy and Martinique. The samples are principally volcanic glass (with minor amounts of mixed materials of various compositions) with silica contents ranging (average values)from 74%(rhyolite) to 57% (andesite). The surface tension components were determined by means of thin-layer wicking to provide contact angles which were used to solve the Young-Dupré equation. The Lifshitz-van der Waals component of the surface tension, γLWLWLWfor these ash samples varies between 26.6 mj/2and 38.7 mj/m2The Lewis acid parameter γ⌖ values are small with values ranging from 0 mJ/m2to 1.8 mJ/m2, while the Lewis base parameter, values varied between 15.6 mJ/m2and 45.6 mJ/m2Of the nine samples, five were hydrophobic and the other four were hy-drophilic. The hydrophobic ashes were produced by eruptions with a dominantly