Glass is a mixture of a large amount of silica that comes from fine white sand or pulverized sandstone, combined with smaller amounts of an alkali like soda (sodium bicarbonate) or potash to lower its melting point, and lime (from limestone) to help stabilize the mixture and ultimately make the glass stronger and water-resistant. These elements are naturally occurring throughout North America.
The silica, soda and lime are fused together at extremely high temperatures. By adding other substances during the process, the properties of the glass can be altered, including its color, how reflective it is, how brilliant or sparkling it looks, how well it acts as an insulator and more. Bits of old or broken glass from previous manufacturing, called ‘cullet’ is usually recycled into the mix. However, it is not just these additives alone that affect the final piece of glass, but also the way in which it is heated, cooled and formed.
First, the silica/soda/lime mixture is heated in melting furnaces to approximately 2,500° Fahrenheit, sometimes for as long as 24 hours. The molten glass is then cooled several hundred degrees, to a temperature at
which it can be worked. At this stage the glass is an orange-red color and looks like a thick liquid. The glass has to be worked quickly to form it into the desired shape, because as the glass cools it becomes hard. The glass can now be blown, pressed, drawn or rolled. Finally, when the glass is formed into the desired shape, it is placed in a ‘lehr’ oven to be ‘annealed.’ This special process eliminates areas of stress in the glass to strengthen it, by cooling it down at controlled temperatures.
Colored glass is made by adding chemicals into the mix, with particular chemicals creating specific colors. For example, the amber or brown glass you see used in beer bottles gets its color from iron sulphide. Iron-chromit
creates shades of green, while cobalt makes beautiful shades of blue.
