Glass is made by combining sand, limestone, soda ash and other minerals at more than 3,000 degrees Fahrenheit. Some substances create color in glass, and glass is formed into windows, windshields, cups, packaging and glazing. Rollers flatten glass into sheets before it is cooled on beds of liquid tin and then cut into the proper sizes in a factory.
When glass heats up, it can be molded into various shapes. The composition of the glass and the temperature at which it cools determines how the glass is used. Glass is found in electronics, automobiles, light bulbs, ceramics and optics. At room temperature, glass gradually droops and sags over many years.
Other ingredients of glass change the chemical composition of the substance and add colors. Lead oxide, alumina and zinc oxide make different types of glass. The substance is 100 percent recyclable, and waste glass makes up between 5 and 40 percent of new material.
Before factories, professional glass blowers used air to form spherical shapes in molten glass. Bits of color are added to vases, ceramics, cups, bowls and plates. Natural, glass-like substances are made in volcanoes in the form of obsidian. Ancient humans used obsidian as arrowheads to hunt animals since the substance is very hard and forms sharp edges.