The true origin of glass making is unknown. What is known, is that the earliest use of glass was most certainly natural glass made by volcanic eruption. Called obsidian, it's a shiny substance that can be black, orange, grey or green in color. Its sharp cutting edges made it a prized possession by prehistoric societies. Another naturally created glass is called fulgurite. Fulgurites are created when lightning strikes sandy soils.
Intentional glass making doesn't appear to have come on the scene until about 3500 B.C. in Mesopotamia. It may have originally been an accidental discovery, caused by sand being left in a ceramic kiln or during the process of copper smelting.
The intentional making of glass involves the superheating of crushed quartzite sand to produce a hot liquid, which is then allowed to cool. 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).
The Egyptians used a method called core-forming. A shaped core was made of clay and dung, then molten glass was wrapped around it and shaped by rolling it on a smooth surface. This creation of glazes for ceramic vessels is considered the first of three technological steps in the invention of glass making.
The second step was the development of molded or cast glass vessels. This process was in use by the Late Bronze Age in Mesopotamia and Egypt. Recently, a primary work shop was discovered at Piramesses, Egypt.
Finally, around the end of the 1st century BC, blown glass appears to have been created by Syrian craftsmen from the Sidon-Babylon area. Using a long thin metal tube, an experienced glassblower could quickly produce intricate and symmetrical shapes out of the "gather" of molten glass at the end of his tube. The tube used in the blowing process has changed very little since then.
With the backing of the powerful and growing Roman Empire, glass products became more accessible to the masses, and the art of glass making spread to many countries across Europe. In fact, during the reign of the emperor Augustus, glass objects began to appear throughout Italy, France, Germany and Switzerland, and even as far away as China. However, it was the Romans who discovered how to create clear glass and use it for architectural purposes. Cast glass windows, although of poor optical quality, began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii.
Around 1,000, eastern and western glassware began to acquire more distinct characteristics. Alexandria remained the most important glass making area in the East, producing luxury glass items mainly for export, while Germanic glassware became less ornate. By the 11th century, German glass craftsmen developed the production of glass sheets. The panes would be joined with lead strips and pieced together to create windows. Glazing remained a great luxury up to the late Middle Ages. 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 colored glass decorated with historical scenes and coats of arms.
In the second half of the 15th century, the craftsmen of Murano, Italy started using quartz sand and potash made from sea plants to produce particularly pure crystal, and by 1688 artisans in France created a new process for the production of plate glass, most often used in mirrors.
Improvements in the quality and processes of glass making continued throughout the Industrial Revolution and are still evolving today. For more information on the history of glass making, visit the following sites: