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Glass does not flow at room temperature as a high-viscosity liquid.http://en.wikipedia.org/wiki/List_of_common_misconceptions#cite_note-Curtin-280 Although glass shares some molecular properties found in liquids, glass at room temperature is an "amorphous solid" that only begins to flow above the glass transition temperature,http://en.wikipedia.org/wiki/List_of_common_misconceptions#cite_note-Halem-281 though the exact nature of the glass transition is not considered settled among theorists and scientists.http://en.wikipedia.org/wiki/List_of_common_misconceptions#cite_note-NYTglass-282 Panes of stained glass windows are often thicker at the bottom than at the top, and this has been cited as an example of the slow flow of glass over centuries. However, this unevenness is due to the window manufacturing processes used at the time. Normally the thick end of glass would be installed at the bottom of the frame, but it is also common to find old windows where the thicker end has been installed to the sides or the top.http://en.wikipedia.org/wiki/List_of_common_misconceptions#cite_note-NYTglass-282 No such distortion is observed in other glass objects, such as sculptures or optical instruments, that are of similar or even greater age. One researcher estimated in 1998 that for glass to actually flow at room temperatures would take many times the age of the earth.
