glass blowing is a technique that dates from roman times
As a novel glass forming technique created in the middle of the 1st century BC, glassblowing exploited a working property of glass that was previously unknown to glassworkers, inflation, the expansion of a molten blob of glass by introducing a small amount of air to it. That is based on the liquid structure of glass where the atoms are held together by strong chemical bonds in a disordered and random network, therefore molten glass is viscous enough to be blown and gradually hardens as it loses heat.
Glassblowing