Core-Formed and Cast Glass
Core-formed and cast glass vessels were first produced in Egypt and Mesopotamia as early as the 15th century BC. 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. In the glass casting technique glass vessels are created by directing molten glass into a mould. Such glass working techniques were spread throughout the Mediterranean by Phoenician merchants.
Glassblowing was then developed by Syrian-Palestinian craftsmen from Sidon and Babylon, between the 1st Century BC and the 1st Century AD, and is thought to have come to Rome with craftsmen and slaves after the area’s annexation by the Roman Empire in 64 BC. Glass was now produced in an easier and quicker way, becoming thinner and more viscous, compared to the initial thicker core-formed and cast glass.
The Invention of Glassblowing
The invention of glassblowing completely revolutionized the production of glass making in the ancient world, and thus became one of the principal and flourishing industries of the Roman Empire. Thanks to the new ease of production, Roman glass became extremely popular and was used to craft many different objects used in daily life: drinking vessels, jars and perfume bottles, amongst many others. Miniature vessels would be used as charms, or even worn as pendants. Blown glass could be made into an array of novel shapes and Roman glass makers seem to have embraced the new change for creativity, with examples of Roman glass in the shape of animals, fruits and many other ambitious shapes having been discovered. Mould-blowing was an alternative glassblowing method, which consisted in a glob of molten glass placed on the end of the blowpipe, and then inflated into a wooden or metal carved mould. In that way, the shape and the texture of the bubble of glass is determined by the design on the interior of the mould.
Colours in Roman Glass
The different colour shades of Roman glass were created by adding specific metal compounds to the basic silica and soda compost. Some colours are more rare than others, such as cobalt blue glass, which was really expensive to produce, and therefore far less commonplace. More common colours included pale blue-green (caused by iron oxide impurities), colourless (in fact an extremely light yellow that appears colourless), amber (made with iron-sulphur compounds) and purple (made with manganese). Aside from variations in colour, the Romans also experimented with new decorative elements such as marbling which was used to create particularly unique and beautiful vessels.