Glass was originally solidified by acidic rocks ejected from volcanoes. Before about 3700 BC, the ancient Egyptians had made glass ornaments and simple glassware. There was only stained glass at that time. About 1000 BC, China made colorless glass. /kloc-in the 0/2 century, commercial glass appeared and began to become an industrial material. /kloc-in the 0/8th century, in order to meet the needs of developing telescopes, optical glass was manufactured. 1873, Belgium made flat glass for the first time. 1906, the United States made flat glass and introduced the machine. Since then, with the industrialization and scale of glass production, glasses with various uses and properties have come out one after another.