The authors report thermal and optical properties of ternary meta-, pyro-, and ortho-zinc tin phosphate glasses, which are glasses that exhibit low glass transition temperature, small photoelastic constants (PECs), and high refractive index. Solid state 31P magic-angle nuclear magnetic resonance, micro-Raman, and infrared spectroscopies are used to characterize the phosphate anions that constitute the glass structure. Glass transition temperatures, thermal coefficient constants, and refractive index are in proportion with ZnO content. Weight loss measurements in water are studied, and then durable glasses are obtained with greater ZnO content. PECs of ternary glasses are dependent on the relative ZnO content. The ratio of measured SnO concentration divided by the fraction of measured phosphate unit predicted the composition with small PEC. High polarizable Sn2+ ions and major dimer phosphate units with non-bridging oxygens are correlated in the very small photoelastic response.