GlassmakingGlass is a uniform, amorphous, solid material.Itis composed mainly of silicon dioxide. This is the major raw material of sand. If raw materials contain as much as 1% iron, the glass will come out colored. So fine glass factories enrich their silicon to make it more pure.When glass is made naturally, it tends to be colored green. This is due to the iron content. But glassblowers add powdered metals to change the color of the glass. By adding sulfur and carbon, glass will become colored yellowish to black. Tin oxide can be used to create white glass. Also, a little cobalt will color glass a deep blue. And small concentrations of selenium can yield a brilliant color known as "selenium ruby."Obsidian is glass that occurs naturally from hot magma flows. This glass has been used to create sharp knives, arrowheads, and tools since the Stone Age. According to history, the first glassmakers were the Phoenicians. They used glass to coat their pottery as early as 3000 B.C.Around 1500 B.C., the ancient Egyptians made glass, jars and beads. The beads they created consisted of metal rods with melted glass wrapped around them. The beads were prized possessions. They were thought to have magic powers.The Romans developed many new glassmaking techniques. They also spread the use of glass as far as China and the British Isles.In Northern Europe, around 1000 A.D., a new method of glasswork was discovered. The use of soda glass was replaced with some other glass contained potash. This was important because potash was much more plentiful. Potash is obtained from wood ashes. From this point on, Northern European and Mediterranean glassworks were distinguishable from each other.In 11th-century Germany, the techniques for making sheet glass were invented. This led to the modern methods of making the windows we use in all houses and buildings. By the 14th century, Venice was the center for fine glassworks. In that city, all sorts of luxury items, such as mirrors, dinnerware, and vases, were made.Hand-blown glass is still considered a commodity to this day. Some of the most famous fine glass artists are Dale Chihuly, Rene Lalique, and Louis Comfort Tiffany. Their works are in museums such as the Smithsonian. Some of their works sell for many thousands of dollars.Cold work techniques are used for turning glass into fine crystal. Crystal manufacturers such as Edinburgh Crystal and Waterford Crystal used diamond saws to cut and polish glass into beautiful designs.The author discusses glass jars and beads in paragraph 4 in order to show that …