Axial gradient index lens blanks with values of (Delta) n up to 0.5, thicknesses and diameters up to 25 and 200 mm, respectively, have been produced by fusing together thin layers of glasses of progressively different indices of refraction. Smooth, step-free gradients are formed by controlled diffusion within and across the layers. Computer software has been developed to prescribe the gradient index profile and to control the diffusion process. Linear, quadratic, cubic, and a variety of other gradient index profiles can be produced by this method over a wide refractive index range. This paper discusses the diffusion software, process and metrology for a gradient blank currently in process to be used in a varifocal slide projector prototype.