obtaining raw materials led to the use of potash instead of soda in Europe, while Italy continued to make soda glass. Sheet glass was developed in Germany in the 11th century, and windows containing panes of glass joined by lead strips, and even stained glass, were emerging towards the end of the Middle Ages.
Venice was the locale for Italian glass making until the end of the 13 century, and a 1271 ordinance banned imported glass and foreign glass makers. In the 14th century, a second Italian glass making industry developed in Altare, which was not strictly controlled like the Venetian industry, and helped extend new styles and techniques of Italian glass to the rest of Europe. In the second half of the 15th century, Italian glass makers were using quartz and potash to produce pure crystal. Lead crystal was developed by an English glass maker in 1674. He began using lead oxide rather than potash to produce a brilliant glass, which was well-suited to deep cutting and engraving.
In 1688, the French developed a new way of making plate glass for use in mirrors in which molten glass was poured onto a special table and rolled flat. After cooling, it was ground using rotating cast iron disks and increasingly fine abrasive sands, then polished with felt disks. A reflective coating was applied to one side to produce a mirror.
The next major change in glass making techniques came with the Industrial Revolution, when German glass maker Otto Schott used scientific methods to examine the effects of various chemicals on the optical and thermal properties of glass. He teamed with Ernst Abbe from the Carl Zeiss firm and they made significant technological advances in glass making. Another major contributor to this technology was Friedrich Siemens, who invented the tank furnace, which allowed the continuous production of greater quantities of molten glass.
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