Ribbed bowls were a staple in ancient glass manufacture since the Hellenistic period, occurring in a variety of colours, sizes and designs. Bowls were manufactured via the cast-form method, wherein molten glass was poured into a mould, then later finished by hand. The ribbing on these pieces would have been achieved either through a specialised mould, or completed by hand with pincers.
Glass manufacture was a key industry in Ancient Rome, with techniques such as core-forming, casting, and glass-blowing creating a variety of tableware, cosmetic vessels, and personal adornments. Different minerals were added to create a variety of colours; the blue tint seen in this piece would have been created by adding cobalt or 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
