Results are presented from a study of the field-assisted diffusion of silver ions from silver films into soda-lime glass. These indicate that it is necessary to take into consideration the concentration dependence of the self-diffusion coefficient of both the silver and the sodium ions in a pseudo-mixed-alkali effect in order to predict the silver diffusion profiles accurately. A field assisted diffusion model that incorporates this effect is developed and model coefficients are deduced. The model is applied to post-bake diffusions and deep field-assisted diffusion profiles. The model is applicable to the design and manufacture of optical waveguides and lenses in glass by field-assisted diffusion.