The verification of a rapid and accurate method of penetration viscometry utilizing a commercial thermal mechanical analyzer with slight modification is described. The viscosity of a National Bureau of Standards Sample Glass No. 711 measured over the range 107 - 1010.7 Pa s showed good agreement with NBS data, with a mean error of 1.2%. The technique was applied to (37AlF3, 12MgF2, 15CaF2, 9SrF2, 12BaF2, 15YF3) and (30.2AlF3, 10.2ZrF4, 3.5MgF2, 20.3CaF2, 13.2SrF2, 10.6BaF2, 8.3YF3, 3.8NaF) (mol %) glasses. No evidence for load-dependent effects was found, and any cessation of penetration was attributable to devitrification during the measurement.