Abstract: A glass block (10) comprises a plurality of intermediate glass plates (12i) stacked between a top plate (12t) and a bottom plate (12b). The top and bottom plate each have a selected composition, with a particular index of refraction and a softening temperature. The intermediate plates have compositions intermediate those of the top and bottom plates and are stacked so as to provide a gradient in composition from top to bottom. Heating the assembly at a fusion temperature fuses the plates together to form the glass block. After cooling down to room temperature, the glass block can be shaped to make lenses and other light directing devices. Such lenses have a gradient in the refractive index of at least about 0.085, and gradients approaching 0.5 are achievable. The thickness of the glass block along the optic axis is fairly unlimited, and thicknesses on the order of 10 mm and more are routinely achievable by the process of the invention.