Editing Glass (section)

== Production ==
{{Main|Glass production|Float glass|Glassblowing}}
[[File:Skansen, Stockholm, Sweden (Unsplash).jpg|thumb|A red hot piece of glass being blown]]
[[File:Float Glass Unloading.jpg|thumb|Industrial robots unloading float glass]]
Following the [[glass batch]] preparation and mixing, the raw materials are transported to the furnace. [[Soda–lime glass]] for [[mass production]] is melted in [[glass melting furnace|glass-melting furnace]]s. Smaller-scale furnaces for speciality glasses include electric melters, pot furnaces, and day tanks.<ref name=ullmann />
After melting, homogenization and [[refining (glass)|refining]] (removal of bubbles), the glass is [[Template:Glass forming|formed]]. This may be achieved manually by [[glassblowing]], which involves gathering a mass of hot semi-molten glass, inflating it into a bubble using a hollow blowpipe, and forming it into the required shape by blowing, swinging, rolling, or moulding. While hot, the glass can be worked using hand tools, cut with shears, and additional parts such as handles or feet attached by welding.<ref name="Brittanica-glass-blowing">{{Britannica|235045|Glassblowing}}</ref>
[[Flat glass]] for windows and similar applications is formed by the [[float glass]] process, developed between 1953 and 1957 by Sir [[Alastair Pilkington]] and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.<ref>{{cite web|url=http://www.pfg.co.za/about%20glass.htm |title=PFG Glass |publisher=Pfg.co.za |access-date=24 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20091106210357/http://www.pfg.co.za/about%20glass.htm |archive-date=6 November 2009}}</ref> [[Container glass]] for common bottles and jars is formed by [[Glass container production#Forming process|blowing and pressing]] methods.<ref>{{Cite book|url=https://books.google.com/books?id=Kbxv0oPJPK4C&pg=PA449|title=Code of Federal Regulations, Title 40,: Protection of Environment, Part 60 (Sections 60.1-end), Revised As of July 1, 2011|date=October 2011|publisher=Government Printing Office|isbn=978-0-16-088907-3}}</ref> This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance.<ref>{{Cite book|url=https://books.google.com/books?id=Pwvtj9jJd6wC&pg=PA552|title=Leachables and Extractables Handbook: Safety Evaluation, Qualification, and Best Practices Applied to Inhalation Drug Products|last1=Ball|first1=Douglas J.|last2=Norwood|first2=Daniel L.|last3=Stults|first3=Cheryl L. M.|last4=Nagao|first4=Lee M.|date=2012-01-24|publisher=John Wiley & Sons|isbn=978-0-470-17365-7|page=552|language=en}}</ref>

Once the desired form is obtained, glass is usually [[annealing (glass)|annealed]] for the removal of stresses and to increase the glass's hardness and durability.<ref name="EB1911">{{Cite EB1911|wstitle=Glass|volume=12|pages=87–105}}</ref> Surface treatments, coatings or [[lamination]] may follow to improve the chemical durability ([[Glass production#Coatings|glass container coatings]], [[Glass production#Internal treatment|glass container internal treatment]]), strength ([[toughened glass]], [[bulletproof glass]], [[windshield]]s<ref>{{cite web|url= https://www.autoglassguru.com/blog/windshields-how-theyre-made/ |title= windshields how they are made|publisher=autoglassguru |access-date=2018-02-09}}</ref>), or optical properties ([[insulated glazing]], [[anti-reflective coating]]).<ref>{{cite web|url=https://www.lehigh.edu/imi/teched/GlassProcess/Lectures/Lecture10_Pantano_Surface_Treatments.pdf |archive-url=https://web.archive.org/web/20150909081808/http://www.lehigh.edu/imi/teched/GlassProcess/Lectures/Lecture10_Pantano_Surface_Treatments.pdf |archive-date=2015-09-09 |url-status=live|title=Glass Surface Treatments: Commercial Processes Used in Glass Manufacture|last=Pantano|first=Carlo}}</ref>

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure [[chemical]]s are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as [[alkali metal|alkali]] or [[alkaline earth metal]] oxides and hydroxides, or [[boron trioxide|boron oxide]]), or that the impurities are quantified (loss on ignition).<ref name="pnnl">{{cite web|url=http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html |title=Glass melting, Pacific Northwest National Laboratory |publisher=Depts.washington.edu |access-date=24 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100505144629/http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html |archive-date=5 May 2010}}</ref> Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., [[sodium selenite]] may be preferred over easily evaporating [[selenium dioxide]] (SeO<sub>2</sub>). Also, more readily reacting raw materials may be preferred over relatively [[Chemically inert|inert]] ones, such as [[aluminium hydroxide]] (Al(OH)<sub>3</sub>) over [[Aluminium oxide|alumina]] (Al<sub>2</sub>O<sub>3</sub>). Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass [[homogeneous (chemistry)|homogeneity]] is achieved by homogenizing the raw materials mixture ([[glass batch]]), stirring the melt, and crushing and re-melting the first melt. The obtained glass is usually [[annealing (glass)|annealed]] to prevent breakage during processing.<ref name=pnnl /><ref>{{cite web |last=Fluegel |first=Alexander |url=http://glassproperties.com/melting/ |title=Glass melting in the laboratory |publisher=Glassproperties.com |access-date=24 October 2009 |url-status=live |archive-url=https://web.archive.org/web/20090213120553/http://glassproperties.com/melting/ |archive-date=13 February 2009}}</ref>

=== Colour ===
{{Main|Glass coloring and color marking}}

Colour in glass may be obtained by addition of homogenously distributed electrically charged ions (or [[Transparent materials#Absorption of light in solids|colour centres]]). While ordinary [[soda–lime glass]] appears colourless in thin section, [[iron(II) oxide]] (FeO) impurities produce a green tint in thick sections.<ref name="Mukherjee13">{{cite book|last=Mukherjee|first=Swapna|title=The Science of Clays: Applications in Industry, Engineering, and Environment|publisher=Springer Science & Business Media|year=2013|pages=142|url=https://books.google.com/books?id=wALFBAAAQBAJ&pg=PA142|isbn=978-9-4007-6683-9}}</ref> [[Manganese dioxide]] (MnO<sub>2</sub>), which gives glass a purple colour, may be added to remove the green tint given by FeO.<ref>{{Cite book|title=CRC Handbook of Metal Etchants|last1=Walker|first1=Perrin|last2=Tarn|first2=William H.|publisher=CRC press|year=1990|page=798|isbn=978-1-4398-2253-1|url=https://books.google.com/books?id=-2ObmTZTq2QC&pg=PA798}}</ref> FeO and [[chromium(III) oxide]] (Cr<sub>2</sub>O<sub>3</sub>) additives are used in the production of green bottles.<ref name="Mukherjee13" /> [[Iron (III) oxide]], on the other-hand, produces yellow or yellow-brown glass.<ref name="Langhamer03">{{cite book|url=https://books.google.com/books?id=UwLCa_h3hTEC&pg=PA273|title=The Legend of Bohemian Glass: A Thousand Years of Glassmaking in the Heart of Europe|first=Antonín|last=Langhamer|pages=273|year=2003|publisher=Tigris|isbn=978-8-0860-6211-2}}</ref> Low concentrations (0.025 to 0.1%) of [[cobalt oxide]] (CoO) produce rich, deep blue [[cobalt glass]].<ref>{{cite journal |title=3. Glass, Colour and the Source of Cobalt |url=https://intarch.ac.uk/journal/issue52/3/3.html |website=Internet Archaeology |doi=10.11141/ia.52.3}}</ref> [[Chromium]] is a very powerful colouring agent, yielding dark green.<ref>[http://www.speclab.com/elements/chromium.htm Chemical Fact Sheet – Chromium] {{Webarchive|url=https://web.archive.org/web/20170815033017/http://www.speclab.com/elements/chromium.htm |date=2017-08-15 }} www.speclab.com.</ref>
[[Sulphur]] combined with [[carbon]] and iron salts produces amber glass ranging from yellowish to almost black.<ref>David M Issitt. [https://web.archive.org/web/20070305020112/http://1st.glassman.com/articles/glasscolouring.html Substances Used in the Making of Coloured Glass] 1st.glassman.com.</ref> A glass melt can also acquire an amber colour from a reducing combustion atmosphere.<ref>{{Cite book|url=https://books.google.com/books?id=-mwoDwAAQBAJ&pg=PA211|title=Introduction to Glass Science and Technology|last=Shelby|first=James E.|year=2007|page=211|publisher=Royal Society of Chemistry|isbn=978-1-84755-116-0}}</ref> [[Cadmium sulfide]] produces imperial [[red]], and combined with selenium can produce shades of yellow, orange, and red.<ref name="Mukherjee13" /><ref name="Langhamer03" /> Addition of [[copper(II) oxide]] (CuO) produces a [[turquoise (color)|turquoise]] colour in glass, in contrast to [[copper(I) oxide]] (Cu<sub>2</sub>O) which gives a dull red-brown colour.<ref name="Nicholson00">{{cite book|url=https://books.google.com/books?id=Vj7A9jJrZP0C&pg=PA208|title=Ancient Egyptian Materials and Technology|first1=Paul T.|last1=Nicholson|first2=Ian|last2=Shaw|publisher=Cambridge University Press|year=2000|pages=208|isbn=978-0-521-45257-1}}</ref>

<!-- WORKING ON FINDING MORE SUITABLE REFERENCES FOR THIS
* [[Nickel]], depending on the concentration, produces blue, or [[violet (colour)|violet]], or even [[black]] glass. [[Lead crystal]] with added nickel acquires purplish colour. Nickel together with a small amount of cobalt was used for decolourizing of [[lead glass]]. -->
<gallery mode="nolines">
File:Bottle, wine (AM 1997.80.28-1).jpg|alt=A green glass bottle|[[Iron(II) oxide]] and [[chromium(III) oxide]] additives are often used in the production of green bottles.<ref name="Mukherjee13" />
File:Bristol.blue.glass.arp.750pix.jpg|alt=Several examples of deep blue glass|[[Cobalt oxide]] produces rich, [[cobalt glass|deep blue glass]], such as [[Bristol blue glass]].
File:Colour Eclipse, Danny Lane.jpg|alt=Three glass disks, with one coloured turquoise, another purple, and a third coloured red|Different oxide additives produce the different colours in glass: [[turquoise (color)|turquoise]] ([[copper(II) oxide]]),<ref name="Nicholson00" /> purple ([[manganese dioxide]]),<ref name="Mukherjee13" /> and red ([[cadmium sulfide]]).<ref name="Mukherjee13" />
File:Chinese snuff bottle, Qing dynasty, glass bottle with amber stopper, Honolulu Museum of Art.JPG|Red glass bottle with yellow glass overlay
File:Glass ornaments.JPG|Amber-coloured glass
File:Glass garland bowl MET DP122006.jpg|Four-colour Roman glass bowl, manufactured {{Circa|1st century B.C.}}
</gallery>