This piece has been created using the ancient sand core technique. The core formed or sand core glass vessels were created when a core of sand, mud or clay was formed around the end of a metal rod. Molten glass was then trailed onto the core to form the body of the vessel and decorative threads of contrasting colours were applied and dragged into various patterns, such as feathers or zigzag designs. This type of glass-working technique was developed in Egypt and Mesopotamia as early as the 15th century BC, subsequently spreading in all the Mediterranean regions.
To learn more about glass in Antiquity, visit our relevant post: How It Was Made: Roman Glass.