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Glass
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When making glass, all the ingredients must first be ground down with mortars. Then the silex and flux are placed in a furnace on medium heat for five or six hours, stirred repeatedly. The resulting substance is known as frit, and it can be easily turned into glass by pounding, blowing, or spinning it. Additional flux and the pyrolusite can be added now as needed to adjust the viscosity (before the shaping). There are many methods for making plate glass (or flat window-pane glass) such as the casting and running method (shown in fig. 7) and the crown method (shown in fig. 6)The crown method of making flat glass (the method most likely to be performed by a fairly primitive society lacking advanced machinery) begins with blowing a large glob of molten glass into a sphere with a blowing iron. Then we reheat the globe, attach it to a pontil, and shape it into a flat-bottomed flask. Next we would cut a hole out of the flat base and heat the glass up again. While still being heated, we would spin the glass on the pontil until the centrifugal stress caused by the spinning made the glass flare out suddenly into a disk shape. Lastly, we would remove the glass from the heat, while continuing to spin it until the glass had cooled enough to keep its shape.
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