Glass was often the preferred material for storing expensive oils, perfumes, and medicines because it was not porous. The small body and mouth of the vessel also allowed the user to carefully pour and control the amount of liquid dispensed. These small glass bottles are found frequently at Hellenistic and Roman sites, especially in cemeteries, and the liquids which filled them would have been gathered from all corners of the expansive Roman Empire.
The iridescence on ancient Roman glass was unintentional, and was caused by weathering on its surface. The extent to which a glass object weathers depends mainly on the burial conditions; however, the humidity, heat, and type of soil in which the glass was buried also all affect its preservation.