Editing Glass (section)

=== Optical ===
{{Main|Optical glass}}
Glass is in widespread use in optical systems due to its ability to refract, reflect, and transmit light following [[geometrical optics]]. The most common and oldest applications of glass in optics are as [[Lens (optics)|lenses]], [[window]]s, [[mirror]]s, and [[Prism (optics)|prism]]s.<ref name="Bach12">{{cite book |title=The Properties of Optical Glass |first1=Hans |last1=Bach |first2=Norbert |last2=Neuroth |publisher=Springer |year=2012|url=https://books.google.com/books?id=y3nnCAAAQBAJ&pg=PA1 |pages=1–11 |isbn=978-3-642-57769-7}}</ref> The key optical properties [[refractive index]], [[Dispersion (optics)|dispersion]], and [[Transparency and translucency|transmission]], of glass are strongly dependent on chemical composition and, to a lesser degree, its thermal history.<ref name=Bach12 /> Optical glass typically has a refractive index of 1.4 to 2.4, and an [[Abbe number]] (which characterises dispersion) of 15 to 100.<ref name=Bach12 /> The refractive index may be modified by high-density (refractive index increases) or low-density (refractive index decreases) additives.<ref>{{Cite book |url=https://books.google.com/books?id=-0DOBQAAQBAJ&pg=PA70 |title=Physical Properties of Materials, Second Edition |last=White |first=Mary Anne |authorlink1=Mary Anne White |year=2011 |pages=70 |publisher=CRC Press|isbn=978-1-4398-9532-0}}</ref>

Glass transparency results from the absence of [[grain boundary|grain boundaries]] which [[diffuse reflection|diffusely scatter light]] in polycrystalline materials.<ref name="Carter-Norton">{{Cite book |url=https://books.google.com/books?id=aE_VQ8I24OoC&pg=PA583 |title=Ceramic Materials: Science and Engineering |last1=Carter |first1=C. Barry |first2=M. Grant |last2= Norton |year=2007| publisher=Springer Science & Business Media| pages=583|isbn=978-0-387-46271-4 }}</ref> Semi-opacity due to crystallization may be induced in many glasses by maintaining them for a long period at a temperature just insufficient to cause fusion. In this way, the crystalline, devitrified material, known as Réaumur's glass [[porcelain]] is produced.<ref name="EB1911-incorp">{{EB1911|inline=1 |wstitle=Glass |volume=12 |page=86}}</ref><ref name="Mysen05">{{cite book|last1=Mysen|first1=Bjorn O.|last2=Richet|first2=Pascal|title=Silicate Glasses and Melts: Properties and Structure|publisher=Elsevier|year=2005|pages=10}}</ref> Although generally transparent to visible light, glasses may be [[Opacity (optics)|opaque]] to other [[Electromagnetic spectrum|wavelengths of light]]. While silicate glasses are generally opaque to [[infrared]] wavelengths with a transmission cut-off at 4 μm, heavy-metal [[Fluoride glass|fluoride]] and [[Chalcogenide glass|chalcogenide]] glasses are transparent to infrared wavelengths of 7 to 18 μm.<ref name=brittanica-industrial /> The addition of metallic oxides results in different coloured glasses as the metallic ions will absorb wavelengths of light corresponding to specific colours.<ref name=brittanica-industrial />