What is Glass?

Glass is that mysterious translucent substance of what is essentially super-heated silica sand.  Early humans in the Mediterranean made glass from a mixture of quartz sand, limestone and soda ash.  These minerals were placed in a pottery kiln and super heated until the contents melted and combined  to form molten glass

Glass is one of the most important human discoveries ranking along side other human inventions such as the wheel, ceramics, metal tools and weaving fabric.  Glass making along with other discoveries helped lift humans out of the stone age.  Ancient glass was made for beads (money and jewellery) and glazing.

In the late bronze age glass blowing and moulding was perfected and gave rise to the use of glass for it’s properties of transparency strength and magnification of light.  As a container glass allowed the user to view the contents and the amount inside without opening the container.

The first manufactured glass in prehistory was made by the Phoenicians in the eastern Mediterranean about 5000 BC. 500 years later in Mesopotamia and Egypt about 3000 BC, heated crushed quartz was used to make glazes for ceramic vessels.  These were probably accidental discoveries made during the firing of pottery kilns then utilised for ongoing pottery production.   The first glass making “manual” dates back to around 650 BC.  Instructions on how to make glass are contained in tablets from the library of the Assyrian King Ashurbanipal (669-626 BC)

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

In the Middle Ages, the Italian city of Venice was the glass making centre of the western world.   The 11th century also saw the development of 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 end 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.  In the 14th century, another important Italian glass making industry developed at Altar, near Genoa.  Its importance lies largely in the fact that it was not subject to the strict statutes of Venice as regards the exporting of glass working skills.  Thus, during the 16th century, craftsmen from Altar helped extend the new styles and techniques of Italian glass to other parts of Europe, particularly France.