Glass is usually produced when molten material cools very rapidly, not giving enough time for a regular crystal lattice to form. It is sometimes created naturally from volcanic flows in the form of obsidian.
Naturally occuring obsidian glass has been used since the stone age. The first documented glass making is in Egypt around 2000 B.C., where sheets of glass were created by the melting of sand on molten lead, which is now called "float glass" as the glass floats to the surface. During the Roman Empire many forms of glass were created, but until the 1100's [stained glass]? (which is glass with some metals added for color) glass was not widely used. Venetian? glass was highly prized between the tenth and fourteenth centuries as they kept the process secret. Around 1688, the process for casting glass was developed, which led to it being a much more commonly used material. The invention of the glass pressing machine in 1827 allowed the mass production of inexpensive glass articles.
Even with the availablity of comman glassware, there remains place for hand blown glassware. Some artists in glass include [Sidney Waugh]?, [René Lalique]?, and [Louis Tiffany]?, who were responsible for extraordinary glass objects. The term "crystal glass", derived from rock crystal, has come to denote high-grade colorless glass and is sometimes applied to any fine hand-blown glass.
It is sometimes claimed that glass may show some of the properties of liquids that flow at room temperature, albeit very slowly. As an example, it is sometimes claimed that old windows are often thicker at the bottom than at the top, and that this might be due to flow. It is a bit unclear where this belief came from, or if there was ever any evidence to support it.
The "glass flows" issue has been discussed at great length in the alt.folklore.urban newsgroup, and the consensus there (supported by citations from glass experts) is that glass does not flow at room temperature.
Arguments against glass flow:
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