The sessile drop method has been used to determine the time dependence of the contact angle at 850 degreesC in vacuo for Ag-28 wt% Cu, Ag-35 wt% Cu-1.5 wt% Ti, and Ag-27 wt% Cu-12 wt% In-2 wt% Ti on vitreous and devitrified fused quartz substrates. Nonwetting behavior (theta > 90 degrees) was observed for Ag-28 wt% Cu on both substrates vvith no evident effect of time at temperature. The silica substrate structure, whether crystalline or amorphous, as well as its surface condition, whether smooth or rough, made no significant difference. In contrast, with Ag-35 wt% Cu-1.5 wt% Ti and Ag-27 wt% Cu-12 wt% In-2 wt% Ti the contact angle continuously decreased with time for both silica substrates, and the structure and surface condition of the substrates had a negligibie effect in the case of Ag-27 wt% Cu-12 wt% In-2 wt% Ti, which produced essentially the same contact angles on both silica substrates at a given time of hold at 850 degreesC. The contact angles produced by Ag-35 wt% Cu-1.5 wt% Ti on devitrified fused quartz were consistently higher than those produced on the vitreous substrates, with increasing holding time at 850 degreesC. This is attributable to the presence of extensive cracks in the alpha -cristobalite layer at the surface of the devitrified substrates, which obstruct wetting and spreading. These results, when correlated with the wettability of preoxidized silicon carbide by the same alloys reported in previous work, could account for the adverse effect on wetting of the high-temperature silica films formed on the surface of the SIC in that work.