Canada>Canada http://ileniafc.altervista.org/phpBB2/profile.php?mode=viewprofile&u=47055 cucumbertube The spin-casting process creates the essential paraboloid shape for the mirror; thanks to the spinning motion, a depression forms in the center of the casting medium as its outer edges rise up the walls of the furnace. In the case of the GMT mirrors, about 21 tons of borosilicate glass flow into a prefabricated mold to form the lightweight honeycomb structure of the mirror; this structure will be very stiff and allow the mirror to adjust rapidly to temperature fluctuations at night, preventing distortion of the images obtained. Once it is cast, the third mirror will be polished to an optical surface accuracy within approximately 25 nanometers.