<P> From there, escaping craftsmen (who had been forbidden to travel) otherwise advanced to the rest of Europe by building their glassblowing workshops in the north of the Alps (which is now Switzerland), and then at sites in northern Europe in present - day France and Belgium . </P> <P> One of the most prolific glassblowing centers of the Roman period was established in Cologne on the river Rhine in Germany by late 1st century BC . Stone base molds and terracotta base molds were discovered from these Rhineland workshops, suggesting the adoption and the application of mold - blowing technique by the glassworkers . Besides, blown flagons and blown jars decorated with ribbing, as well as blown perfume bottles with letters CCAA or CCA which stand for Colonia Claudia Agrippiniensis, were produced from the Rhineland workshops . Remains of blown blue - green glass vessels, for example bottles with a handle, collared bowls and indented beakers, were found in abundance from the local glass workshops at Poetovio and Celeia in Slovenia . </P> <P> Surviving physical evidence, such as blowpipes and molds which are indicative of the presence of blowing, is fragmentary and limited . Pieces of clay blowpipes were retrieved from the late 1st century AD glass workshop at Avenches in Switzerland . Clay blowpipes, also known as mouthblowers, were made by the ancient glassworkers due to the accessibility and availability of the resources before the introduction of the metal blowpipes . Hollow iron rods, together with blown vessel fragments and glass waste dating to approximately 4th century AD, were recovered from the glass workshop in Mérida of Spain, as well as in Salona in Croatia . </P> <P> The glass blowing tradition was carried on in Europe from the medieval period through the Middle Ages to the Renaissance in the demise of the Roman Empire in the 5th century AD . During the early medieval period, the Franks manipulated the technique of glassblowing by creating the simple corrugated molds and developing the claws decoration techniques . Blown glass objects, such as the drinking vessels that imitated the shape of the animal horn were produced in the Rhine and Meuse valleys, as well as in Belgium . The Byzantine glassworkers made mold - blown glass decorated with Christian and Jewish symbols in Jerusalem between late 6th century and the middle of the 7th century AD . Mold - blown vessels with facets, relief and linear - cut decoration were discovered at Samarra in the Islamic lands . </P>

Short note on glass blowing as an art