  We estimate the loss angles of the materials currently used in the highly
reflective test-mass coatings of interferometric detectors of gravitational
waves, namely Silica, Tantala, and Ti-dop ed Tantala, from direct measurement
of coating thermal noise in an optical interferometer testbench, the Caltech
TNI. We also present a simple predictive theory for the material properties of
amorphous glassy oxide mixtures, which gives results in good agreement with our
measurements on Ti-doped Tantala. Alternative measure ment methods and results
are reviewed, and some critical issues are discussed.
