(a–e) Yellowish organic film covering the crystal grains on experimental GSTs used to process oat (a), downy brome (b), wild grass grains (c), and millet (d); smooth domed and flat micropolish developing over the high and low microtopographies associated with oat (Avena barbata) grinding; (f) smooth flat and domed micropolish developing over the surface high and low microtopographies and characterized by narrow microstriations associated with grinding downy brome (Bromus tectorum L.); (g) smooth flat micropolish developed over the high and low microtopographies characterized by sporadic narrow striations associated with grinding wild grass grains (Aegilops ventricosa Tausch); (h) smooth domed polish developed over the high and low microtopographies associated with the grinding of foxtail millet (Setaria italica (L.) P. Beauvois); (i–l) spots of organic film, yellowish in color covering the crystal grains across the surface of archaeological GSTs; smooth domed micropolish identified on archaeological GSTs developing over the high and low surface microtopographies and associated with microstriations (m-o). Starch granules identified on archaeological GSTs. (q) Type I (GST no. INV.80); (r) Type I (GST no. INV.146); (s) Type III (GST no. INV.28); (t) Type VI (GST no. INV.67); (u) Type VI (GST no. INV.10); (v) Type VI (GST no. INV.146); (w) Type I (GST no. INV.71).