Increased trade on the Silk Road in the 200s BC forced traders to try to come up with new things to trade that other people would want. West Asia was already way ahead of China, India, Europe, and Africa in glass-making, so West Asian glass-makers looked for some way to make their glass even more exciting to traders.
Around 75 BC, the Phoenicians figured it out: a new, much better way to make glass, much faster and cheaper than before. They learned to blow glass. You stick a gob of hot glass onto the end of a long clay pipe, and you blow through the pipe as if you were blowing up a balloon. The air makes the gob of glass blow up, just like a balloon. Then as you blow you can shape the glass with a metal stick. This isn’t easy,but it is a lot easier than making core-formed glass!
Blowing glass at the Corning Museum in New York State
Soon after this, the Phoenicians also figured out how to just blow the glass right into a mold (this is called mold-blown glass). Then you don’t even have to shape it yourself, and you can get all sorts of fancy shapes. Glass became cheap enough to replace pottery cups for most people, and was very widely used all over the Roman Empire and the Parthian Empire.
Glass became one of West Asia’s main products for the Silk Road (so much that Chinese traders often called it the Glass Road) and international trade. By around 200-300 AD, glass-blowers were using iron pipes instead of clay ones.
There were big centers of glass production not only in Phoenicia but also further west in modern Köln (northern Germany) and other places around the Roman Empire, and further east in the Parthian Empire and at Taxila (modern Iraq and Pakistan). Roman and Parthian traders shipped glass through Central Asia and India as far as East Africa and China and Japan.
It wasn’t only the Romans and Parthians making glass, either. Indian glass factories at Arikamedu made glass beads and plaques that they sold as far east as the Philippines and west to West Africa. Southern Chinese factories made beads and plaques, but they didn’t make blown glass.
Learn by doing: go see someone blowing glass
More about glass – medieval and modern glass
How Glass Is Made, by Alan J. Paterson (1985). Easy reading, but it’s really about modern glass technology.
Studies in Ancient Technology: Leather in Antiquity – Sugar and Its Substitutes in Antiquity – Glass, by R. J. Forbes (2nd revised edition 1997). Only part of the book is about glass, but it will tell you everything you need to know about glass in ancient Greece and Rome. By a specialist, for adults.
Early Glass of the Ancient World: 1600 B.C.-A. D. 50, by E. M. Stern (1995). Marianne Stern is the leading world expert on ancient glass.
Roman, Byzantine and Early Medieval Glass: Ernesto Wolf Collection, by E. M. Stern and others (2002). Same expert author as above.