A little about the making of glass - Part III

by Evelyn Allen
Issue #18 - October 1974

Let's explore the raw materials in glass. The finest grade of Silica Sand is found here in the Western Hemisphere, the widest known deposits are in the states of New Jersey, Pennsylvania, and Illinois. Sand is one of the most important factors in the making of good glass. Soda Ash is manufactured from salt -- this is in plentiful supply in the United States. Potash, formerly imported, in recent years has become a product supplied by the Chemical Industry of America. The special salts for Potash are found in California, Texas, New Mexico and other states. Nitrate of Soda and Nitrate of Potash are manufactured from raw materials and are also obtainable as natural minerals. Lime in its natural form of Limestone is found in abundance all over the United States. It is used in either of two ways; as ground raw limestone or as Burned Lime. Lead Oxide, called glass-makers lead, is manufactured from metallic lead.

Ruby or red glasses are nearly always made by adding Metallic Selenium and Sulfide of Cadmium to the glass "batch." Ruby glass can also be made with gold or copper. Green glass is made with either Chrome Oxide or Chrome Salts. Copper and Cobalt Oxides will color glass blue; Nickel will color grey. Iron will color Brown or green, depending on the manner in which it is used. Various mixtures will give various tints. Glass is a complex Silicate. Although glass is "clear" when finished, practically none of its elements are transparent.

Glass is melted from a "batch" of raw materials consisting usually of Silica Sand, Soda-Ash, Potash, Lime or Lead. The raw materials are carefully weighed and by the aid of mixing devices, blended into a uniform mass. At this stage all the raw materials are brought together and a certain amount of broken glass commonly called cullet, is added. The weight and handling operation of the materials are dusty and the men performing this work are protected by respirators or other modern safety devices. The "batch" is put into a mixing drum, which resembles a cement mixer. During shipping or in handling, impurities may get into the batch. The batch is emptied from the mixing drum onto a conveyor belt which carries it over a magnet; the magnet serves to catch and withdraw foreign matter. The mixed batch is then taken to pots or tanks for melting. More on that next month.