100 A.D.
The Roman connection
The Romans also did much to spread glassmaking technology. With its conquests, trade relations, road building, and effective political and economical administration, the Roman Empire created the conditions for the flourishing of glassworks across western Europe and the Mediterranean. During the reign of the emperor Augustus, glass objects began to appear throughout Italy, in France, Germany and Switzerland. Roman glass has even been found as far afield as China, shipped there along the silk routes.
It was the Romans who began to use glass for architectural purposes, with the discovery of clear glass (through the introduction of manganese oxide) in Alexandria around AD 100. Cast glass windows, albeit with poor optical qualities, thus began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii.
With the geographical division of the empires, glass craftsmen began to migrate less, and eastern and western glassware gradually acquired more distinct characteristics. Alexandria remained the most important glassmaking area in the East, producing luxury glass items mainly for export. The world famous Portland Vase is perhaps the finest known example of Alexandrian skills. In Rome's Western empire, the city of Köln in the Rhineland developed as the hub of the glassmaking industry, adopting, however, mainly eastern techniques. Then, the decline of the Roman Empire and culture slowed progress in the field of glassmaking techniques, particularly through the 5th century. Germanic glassware became less ornate, with craftsmen abandoning or not developing the decorating skills they had acquired.
11th century
Sheet glass skills
The 11th century also saw the development by German glass craftsmen of a technique - then further developed by Venetian craftsmen in the 13th century - for the production of glass sheets. By blowing a hollow glass sphere and swinging it vertically, gravity would pull the glass into a cylindrical "pod" measuring as much as 3 metres long, with a width of up to 45 cm. While still hot, the ends of the pod were cut off and the resulting cylinder cut lengthways and laid flat. Other types of sheet glass included crown glass (also known as "bullions"), relatively common across western Europe. With this technique, a glass ball was blown and then opened outwards on the opposite side to the pipe. Spinning the semi-molten ball then caused it to flatten and increase in size, but only up to a limited diameter. The panes thus created would then be joined with lead strips and pieced together to create windows. Glazing remained, however, a great luxury up to the late Middle Ages, with royal palaces and churches the most likely buildings to have glass windows. Stained glass windows reached their peak as the Middle Ages drew to a close, with an increasing number of public buildings, inns and the homes of the wealthy fitted with clear or coloured glass decorated with historical scenes and coats of arms.
Possibly, but high quality didn't emerge until 1,000 years later.