High temperature viscoelastic properties of two different silicate glass melts have been measured with a new high temperature rheometer between 700 and 900degreesC. Our experiments demonstrate that the viscoelastic properties in the terminal zone, a low frequency domain which has never been explored. are very sensitive to the chemical composition of the glass and to the thermal treatment applied during the preparation of the samples. The storage shear modulus G' and the loss shear modulus G" were measured at constant temperature between 10(-3) and 10(2) rad/s. The two chosen silicate glass melts have different chemical compositions and moreover one of them was prepared with two thermal treatments during the sample molding. In the experimental range of temperature, the viscoelastic properties of the two glass melts are characteristic of the ultimate theological behavior at low frequencies called the terminal zone. We tested the possibility of building the rheological master curve of the two liquids over a wide frequency domain. Experiments show that one glass melt has a Maxwell viscoelastic behavior and obeys time-temperature superposition. Its master curve shows that the glass melt follows the Williams-Landel-Ferry equation. On the other hand, the second glass is non-Maxwellian and does not obey time-temperature superposition. In that case, the master curve cannot be built showing a phase transition, or structural change transition, between 700 and 900 degreesC. (C) 2004 Elsevier B.V All rights reserved.