Glass is made by heating chemicals in a glass furnace until they melt into molten glass. This liquid is then formed into shape and slowly cooled to prevent breaking. Glassblowing is an ancient art still practiced today. Modern industrial glass production uses a process called float glass to create sheet glass or window glass.
A glass furnace is a specialized furnace used in the production of glass. The chemicals are heated together in a glass furnace to their melting point, when they melt into molten glass. This liquid can then be formed into the shape it will hold when it cools and solidifies. The glass furnace allows glaziers to control the temperature of the glass, so it doesn’t break or lose its shape as it cools.
Glass making dates back thousands of years. The earliest glass kilns were probably kilns built for pottery, an even older craft. The first production of glass was introduced by the Egyptians and then developed by the Phoenicians and Romans in the following centuries. Much of ancient glass was formed from the practice of glassblowing, an art which is still practiced into the 21st century.
Even the first window panes were made by glass blowing; the processes were complicated, because blown glass generally takes on a round shape. Some sheet glass was made by cutting and shaping glass cylinders, a process that had to be completed quickly after the glass was removed from the furnace. The process was imperfect and the quality of the plates varied greatly until better industrial processes were created in the 20th century.
In glassblowing, molten glass is held in a specially shaped glass furnace. The glassblower collects a quantity of liquid glass on a hollow rod, then causes the glass to expand by blowing air through the unheated end of the rod. The blower keeps the glass at the optimum temperature by working fast and heating the glass in a glory hole, a special opening in the glass furnace for this purpose. Once formed, the glass is placed in another special glass furnace to slowly cool to room temperature without breaking, a process called annealing.
Modern industrial glass production works on much the same principles, only on a larger scale. Sheet glass or window glass is made by heating chemicals in a glass furnace, then delivering the molten glass to the surface of a river of molten tin or other metal; this process is known as float glass, because the glass “floats” on the surface of the metal. Liquid metal has a perfectly flat surface, and glass mimics this property as it slowly cools. Pressurized nitrogen keeps the top surface level of the glass and the rollers allow for a range of thicknesses. Once annealed, the glass can be cut into sheets or plates with special machinery.
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