Throughout the Near- and Mid- East, the Mediterranean and Europe, plant ash appears to have been the main source of alkali for glass from the beginnings of glassmaking in the 3rd millennium BC until around the 9th century BC. These types of glasses contain greater than about 2 wt% K₂O. From about the 9th century BC onward, glasses containing lower K₂O are commonly found in the archaeological record, sometimes alongside plant ash glasses, and are considered to have been made with mineral alkali. The type of alkali chosen by a glassmaker will determine the chemistry of the quartz source necessary to make a workable glass. Plant ashes normally contain significant amounts of CaO such that if more CaO is added from another source, the glass can become too viscous and may crystallize a calcium silicate phase. If plant ashes are used to make glass, then a quartz source with low CaO is usually required, for example vein quartz or relatively pure quartz-sand. Such a quartz source would be expected to contain low levels of impurities such as Al₂O₃. In this study, microprobe analyses of a suite of glasses from Hasanlu, a 10th - 9th c BC site in northwestern Iran, will be used to identify mineral and plant ash groups of glasses. The chemical compositions will also be compared for similarities, and inferences will be made on whether the glasses were made in an industry where information was shared or well-known or whether manufacturing centers had little communication with each other.