We wish to better understand the influence of a common modifier in optical tellurite glasses, zinc. The aim is to relate structural changes in zinc tellurite glasses with the addition of modifier to the functional properties, such as Tg, density and optical response. To achieve this we propose to study a series of zinc tellurite glasses, x ZnO− (1-x) TeO2, where x = 5-50 mol.%, using neutron diffraction and X-ray diffraction (using the ISIS Ag X-ray diffractometer). Building upon previous work, a combination of direct fitting and computational analysis will then be used to determine the coordination numbers of tellurium, nTeO, and zinc, nZnO.