The invention of glass-blowing revolutionised the art of glass-making in the 1st century BC. The new technique allowed craftsmen to use smaller amounts of glass for each vessel and obtain much thinner walls, so enabling the creation of a variety of glass containers in new forms. Different minerals were added to create a variety of colours; the light green tint seen in this piece would have been created by adding copper and changing the oxygen levels. 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.
To find out more about Roman glass, please see our relevant blog posts: Ancient Glass and Collecting Guide: Ancient Roman Glass
