Contributors: Shaoyi Qian
Solarization refers to the color change that occurs in a material as a result of exposure to high-energy electromagnetic radiation, such as UV light or X-rays. In the case of glass, exposure to UV light can induce color in originally colorless, transparent glasses by photo-oxidizing the decolorizers in them. Solarized glasses with various shades of purple are the most commonly found since manganese dioxide has been one of the most common decolorizers. Plastics can undergo this change too. (The Corning Museum of Glass 2011)
irradiated glass, solarized glass, desert glass
Synonyms in English
Most glasses contain silica introduced in the form of sand as a raw material. Although silica itself is colorless, the iron impurity in the sand can impart a greenish tint to the final product. To offset the greenish color and produce colorless glasses, decolorizers are added to a molten glass. One of the most common decolorizers is manganese dioxide (Mn4+). The manganese oxidizes ferrous ions (Fe2+) to ferric ions (Fe3+), which has a yellowish color much less intense than the green color of Fe2+, while itself being reduced to Mn2+ and turning virtually colorless. However, after long exposure to UV light, Mn2+ will be photo-oxidized to Mn3+, which even in rather low concentrations, imparts a pinkish or purplish color to glass. The color of the solarized glass varies depending on the type of the decolorizers. For example, colors ranging from yellow to amber are said to be seen on glasses using selenium or cerium as decolorizers. Just like manganese, selenium and cerium are reduced, during the decolorizing process, from Se4+ to Se2+ and from Ce3+ to Ce2+ respectively. High-energy radiation can again photo-oxidize Se2+ and Ce2+ to higher oxidation states. Other factors that can affect this color interaction include the presence of sulphur (SO3+) and various transition metal ions at concentrations of 0.5% and above. (Abd-Allah 2009)
The optical properties of glass, especially the transmittance and transparency ratio, may also be changed by solarization. Radiation such as UV light can generate defects in the crystalline structure of solids, called color-centers or F-centers, inducing color in transparent glass (Gordon 1959). These color-centers will lead to a reduced transmittance of light. The influence that solarization has on the transmittance of visible light through glass depends on the glass type and its composition as well as on the wavelength of radiation. For example, glass with a high lead content normally exhibits only small solarization effects. Solarization can also cause permanent changes in the physical or mechanical properties of glass. (Abd-Allah 2009)
The Corning Museum of Glass. 2011. "Solarized Glass." Accessed May 3, 2019. https://www.cmog.org/article/solarized-glass.
Abd-Allah, Ramadan. 2009. "Solarization Behavior of Manganese-containing Glass: An Experimental and Analytical Study." Mediterranean Archaeology and Archaeometry 9, no. 1: 37-53. http://maajournal.com/Issues/2009/FullTextAbdAllah.pdf.
Gordon, Robert B. 1959. "Colors Centers in Crystals." American Scientist 47, no. 3: 361-375. https://www.jstor.org/stable/pdf/27827373.pdf