glass formation through the directional properties of bonds. Non-crystallinity is thus favored in elements with a large number of polymorphic forms and a high degree of bonding anisotropy. Crystallization becomes more unlikely as bonding anisotropy is increased from isotropic metallic to anisotropic metallic to covalent bonding, thus suggesting a relationship between the group number in the periodic table and the glass forming ability in elemental solids. Testing for glass transition. Temperatures may have to be tested such as glass quartz around 2000 degrees Fahrenheit as shown above. Glass structure can be determined using infrared and Raman spectroscopy. IR rays are good mostly for silicate glasses and helps find water impurities. IR limited penetration to 1 to 25 micrometers. Electron microscopes and transmission electron microscopes can see structures to around 5 to 10 nanometers, however sample needs to be very smooth and have to interpret glass cluster variations due to electron interactions with differing terrain of glass at that scale. Chemical treatment and analysis is also used but is quite complex and prone to mistakes or contamination. See also Gardner transition Glass formation References External links Fragility VFT Eqn. Polymers I Polymers II Angell: Aqueous media DoITPoMS Teaching and Learning Package- "The Glass Transition in Polymers" Glass Transition Temperature short overview Cryobiology Glass engineering and science Glass physics Phase transitions Polymer chemistry Rubber properties Threshold temperatures