New measurements are presented on the absorption of silver thiogallate and related to fundamental mechanisms. All available data on the refractive indices of silver thiogallate, including new results for the visible, have been incorporated into sets of Sellmeier expressions. Different Sellmeier constants are given for visible and infrared wavelengths and also for crystals from different sources. Confirmation of some predictions from these Sellmeier expressions has been obtained by second-harmonic generation (SHG) experiments with a tunable optical parametric oscillator. Preliminary results on laser damage are summarized.