Glass

Ordinary window gla is a silicate of calcium and sodium, made by heating together lime, sand, and soda; the purer the materials, the better the gla . Plate gla is made of the same materials, but when in a molten condition it is run into molds instead of being blown. Colors are given to gla gla by adding various substances: copper oxide makes a red gla ; compounds of cobalt, blue, chromium and copper, green. The color of bottle gla is due to impurities. Gla , ANCIENT. The art of the gla -blower is represented in paintings of the Fifth Dynasty of Egypt, but the oldest-dated entire ve el is a small, polychromatic vase of opaque gla of the time of Thothmes IV.. ab. 1000 В.С. The Phenic i ans are no longer considered the fathers of this art, which they obtained from Egypt. Syria continued an important center of the manufacture until late in the Middle Ages. From Egypt and Syria the art was transferred to Greece and Rome In Greece gla was a rarity in the 5th century B.C. Its use grew rapidly after that time. The finest collections of ancient gla are the Slade, of the British Museum, and the Charoet, of the N.Y. Metropolitan Museum. The most famous piece of ancient The Portland Vase (British Museum). gla is the Portland Vase in the British Museum. It was found ab. the middle of the 16th century 21 m. from Rome. It is cameo-gla , white on a blue ground 10 in. high. for the opening of the Chicago Auditorium.