# Silvering > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Silvering > Markdown URL: https://mediated.wiki/source/Silvering.md > Source: https://en.wikipedia.org/wiki/Silvering > Source revision: 1323277565 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{short description|Application of reflective coatings to mirrors}} {{About|the process of applying a metallic surface to glass|the application of silver to a metal surface using mercury|Mercury silvering|the use of electricity to apply metal coating to an object|Electroplating|the formation of metallic silver in photographic film|Photographic printing#Silver mirroring}} [[File:Silver mirror reaction.jpg|thumb|upright|Silvering on the inside of a glass [test tube](/source/test_tube)]] '''Silvering''' is the [chemical](/source/chemistry) process of coating a non-conductive substrate such as [glass](/source/glass) with a [reflective](/source/reflectivity) substance, to produce a [mirror](/source/mirror). While the metal is often [silver](/source/silver), the term is used for the application of any reflective metal. ==Process== Most common household mirrors are "back-silvered" or "second-surface", meaning that the light reaches the reflective layer after passing through the glass. A protective layer of [paint](/source/paint) is usually applied to protect the back side of the reflective surface. This arrangement protects the fragile reflective layer from corrosion, scratches, and other damage. However, the glass layer may absorb some of the light and cause distortions and [optical aberration](/source/optical_aberration)s due to [refraction](/source/refraction) at the front surface, and multiple additional reflections on it, giving rise to "ghost images" (although some optical mirrors such as [Mangin mirror](/source/Mangin_mirror)s take advantage of it). Therefore, precision [optical](/source/optics) mirrors normally are "front-silvered" or "[first-surface](/source/first-surface_mirror)", meaning that the reflective layer is on the surface towards the incoming light. The substrate normally provides only physical support, and need not be transparent. A hard, protective, transparent overcoat may be applied to prevent [oxidation](/source/oxidation) of the reflective layer and scratching of the metal. Front-coated mirrors achieve reflectivities of 90–95% when new. == History == [[File:Aluminizing tank.jpg|thumb|upright|Aluminising tank at [Mont Mégantic Observatory](/source/Mont_M%C3%A9gantic_Observatory) used for re-coating telescope mirrors.]] [Ptolemaic](/source/History_of_Ptolemaic_Egypt) [Egypt](/source/Egypt) had manufactured small glass mirrors backed by [lead](/source/lead), tin, or [antimony](/source/antimony). In the early 10th century, the Persian scientist [al-Razi](/source/Muhammad_ibn_Zakariya_al-Razi) described ways of silvering and [gilding](/source/gilding) in a book on [alchemy](/source/alchemy),{{citation needed|date=October 2016}} but this was not done for the purpose of making mirrors. Tin-coated mirrors were first made in [Europe](/source/Europe) in the 15th century. The thin tinfoil used to silver mirrors was known as "tain".{{cite OED1 |tain}} When glass mirrors first gained widespread usage in Europe during the [16th century](/source/16th_century), most were silvered with an [amalgam](/source/amalgam_(chemistry)) of [tin](/source/tin) and [mercury](/source/mercury_(element)). In 1835 [German](/source/Germany) [chemist](/source/chemist) [Justus von Liebig](/source/Justus_von_Liebig) developed a process for depositing silver on the rear surface of a piece of glass; this technique gained wide acceptance after Liebig improved it in 1856. The process was further refined and made easier by the chemist Tony Petitjean (1856). This reaction is a variation of the [Tollens' reagent](/source/Tollens'_reagent) for aldehydes. A solution of [diamminesilver](/source/diamminesilver)(I) is mixed with a sugar and sprayed onto the glass surface. Silver(I) oxidizes the sugar, reducing itself to silver(0), i.e. elemental [silver](/source/silver), which deposits onto the glass. In 1856-1857 [Karl August von Steinheil](/source/Karl_August_von_Steinheil) and [Léon Foucault](/source/L%C3%A9on_Foucault) introduced the process of depositing an ultra-thin layer of silver on the front surface of a piece of glass, making the first optical-quality [first-surface](/source/first-surface_mirror) glass mirrors, replacing the use of [speculum metal](/source/speculum_metal) mirrors in [reflecting telescope](/source/reflecting_telescope)s.{{dead link|date=February 2023}} These techniques soon became standard for technical equipment. An aluminum vacuum-deposition process invented in 1930 by Caltech physicist and astronomer [John Strong](/source/John_D._Strong), led to most reflecting telescopes shifting to aluminum. Nevertheless, some modern telescopes use silver, such as the [Kepler Space Telescope](/source/Kepler_(spacecraft)). The ''Kepler'' mirror's silver was deposited using [ion-assisted evaporation](/source/electron-beam_physical_vapor_deposition). == Modern silvering processes == {{See also|Electroplating|Electroless deposition|Vacuum deposition}} [[File:Silvering of glass ornaments Lauscha.jpg|thumb|right|220px|To speed up the reaction process of the silver, the ornaments are shaken in hot water, [Lauscha](/source/Lauscha)]] ===General processes=== Silvering aims to produce a non-crystalline coating of [amorphous metal](/source/amorphous_metal) (metallic glass), with no visible artifacts from grain boundaries. The most common methods in current use are [electroplating](/source/electroplating), chemical "wet process" deposition, and [vacuum deposition](/source/vacuum_deposition). Electroplating of a substrate of glass or other non-[conductive](/source/Electrical_conductivity) material requires the deposition of a thin layer of conductive but transparent material, such as carbon. This layer tends to reduce the adhesion between the metal and the substrate.{{rp|style=ama|pp= 3 & 107}} Chemical deposition can result in better adhesion, directly or by pre-treatment of the surface. Vacuum deposition can produce very uniform coating with very precisely controlled thickness. ===Metals=== ====Silver==== The reflective layer on a second-surface mirror such as a household mirror is often actual silver. A modern "wet" process for silver coating treats the glass with [tin(II) chloride](/source/tin(II)_chloride) to improve the bonding between silver and glass. An activator is applied after the silver has been deposited to harden the tin and silver coatings. A layer of copper may be added for long-term durability. Silver would be ideal for telescope mirrors and other demanding optical applications, since it has the best initial front-surface reflectivity in the visible spectrum. However, it quickly [oxidizes](/source/Silver_oxide) and absorbs atmospheric [sulfur](/source/Silver_sulfide) to create a dark, low-reflectivity tarnish. ====Aluminum==== The "silvering" on precision optical instruments such as telescopes is usually aluminum. Although aluminum also oxidizes quickly, the thin aluminum oxide (sapphire) layer is transparent, and so the high-reflectivity underlying aluminum stays visible. In modern aluminum silvering, a sheet of glass is placed in a [vacuum](/source/vacuum) chamber with electrically heated [nichrome](/source/nichrome) coils that can evaporate aluminum. In a vacuum, the hot aluminum atoms travel in straight lines. When they hit the surface of the mirror, they cool and stick. Some mirror makers evaporate a layer of [quartz](/source/quartz) or [beryllia](/source/Beryllium_oxide) on the mirror; others expose it to pure [oxygen](/source/oxygen) or air in an oven so that it will form a tough, clear layer of [aluminum oxide](/source/aluminum_oxide). ====Tin==== The first tin-coated glass mirrors were produced by applying a tin–mercury amalgam to the glass and then heating the piece to evaporate the mercury. ====Gold==== The "silvering" on infrared instruments is usually gold. It has the best reflectivity in the infrared spectrum, and has high resistance to oxidation and corrosion. Conversely, a thin gold coating is used to create optical filters which block infrared (by reflecting it) while passing visible light. ==See also== * [Dielectric mirror](/source/Dielectric_mirror) * [List of telescope parts and construction](/source/List_of_telescope_parts_and_construction) * [Optical coating](/source/Optical_coating) * [Mercury glass](/source/Mercury_glass) * [Mercury silvering](/source/Mercury_silvering) * [Metallizing](/source/Metallizing) ==References== {{reflist|25em|refs= {{cite web |title=Ball Aerospace completes primary mirror and detector array assembly milestones for Kepler Mission |date=25 September 2007 |publisher=Ball Aerospace and Technologies Corp. |website=spaceref.com |url= http://www.spaceref.com/news/viewpr.html?pid=23610 |access-date=6 April 2013 }} {{cite web |title=Daily events and images of the installation of the BBSO New Solar Telescope |publisher=[Big Bear Solar Observatory](/source/Big_Bear_Solar_Observatory) |type=blog |url=http://www.bbso.njit.edu/telblog/section4.html |website=www.bbso.njit.edu |access-date=6 January 2020 }} {{cite web |first=Kathleen Payne |last=de Chavez |date=Spring 2010 |title=Historic mercury amalgam mirrors: History, safety, and preservation |website=Williamstown Art |url=http://www.williamstownart.org/techbulletins/images/WACC%20Historic%20Mercury%20Mirrors.pdf |access-date=2014-03-11 }} {{cite magazine |first=Jim |last=Destefani |date=March 2008 |title=Mirror, mirror: Keeping the Hale Telescope optically sharp |magazine=[Products Finishing](/source/Products_Finishing) Magazine |id=PF mag article 030805 |url=http://www.pfonline.com/articles/030805.html |archive-url=https://web.archive.org/web/20091011082949/http://www.pfonline.com/articles/030805.html |archive-date=2009-10-11 }} {{cite web |first=Helen |last=Fioratti |title=The Origins of Mirrors and their uses in the Ancient World |website=L'Antiquaire & the Connoisseur |url=http://www.lantiquaire.us/origins-of-mirrors.html |access-date=2009-08-14 |url-status=dead |archive-url=https://web.archive.org/web/20110203052336/http://www.lantiquaire.us/origins-of-mirrors.html |archive-date=2011-02-03 }} {{cite journal |last1=Fulton |first1=L. Michael |last2=Dummer |first2=Richard S. |year=2011 |title=Advanced Large Area Deposition Technology for Astronomical and Space Applications |journal=Vacuum & Coating Technology |volume=2011 |issue=December |pages=43–47 |url=http://e-ditionsbyfry.com/Olive/ODE/VTC/Default.aspx?href=VTC/2011/12/01 |access-date=6 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130512233653/http://e-ditionsbyfry.com/Olive/ODE/VTC/Default.aspx?href=VTC%2F2011%2F12%2F01 |archive-date=12 May 2013 }} {{cite AV media |number=305 |series=[How It's Made](/source/How_It's_Made) |title=Episode 305 |place=[Anjou, Quebec](/source/Anjou%2C_Quebec), Canada |quote=Episode 305 filmed at [http://www.laverreriewalker.com/ Verrerie-Walker]. }} {{cite journal | first = Justus | last = Liebig | author-link = Justus Liebig | year = 1835 | title = Ueber die Producte der Oxydation des Alkohols |language=de | trans-title = Regarding the products of oxidation of alcohols | journal = [Annalen der Chemie](/source/Liebigs_Annalen) | volume = 14 | issue = 2 | pages = 133–167 | doi = 10.1002/jlac.18350140202 | bibcode = 1835AnP...112..275L | url = https://zenodo.org/record/1426914 }} {{cite journal | first = Justus | last = Liebig | author-link = Justus Liebig | year = 1856 | title = Ueber Versilberung und Vergoldung von Glas |language=de | trans-title = Regarding the silvering and gilding of glass | journal = [Annalen der Chemie und Pharmacie](/source/Liebigs_Annalen) | volume = 98 | issue = 1 | pages = 132–139 | doi = 10.1002/jlac.18560980112 | url = https://zenodo.org/record/1427076 }} {{cite patent | country = GB | number = 1681 | status = patent | title = Silvering, Gilding, and Platinizing Glass | gdate = 1856-01-12 | fdate = 1855-07-24 | inventor-last = Petitjean | inventor-first = Tony | url = https://books.google.com/books?id=nQcADAPqbO0C&q=anthony+petitjohn+silvering&pg=RA29-PA7 }} {{cite book |first1=H.K. |last1=Pulker |date=1999-03-29 |title=Coatings on Glass |publisher=[Elsevier Science](/source/Elsevier_Science) |url=https://books.google.com/books?id=ho2pYhOiEMcC |isbn=9780080525556 }} {{cite web |title=Era of huge reflectors, page 2 |series=Amazing-space |website=[Space Telescope Science Institute](/source/Space_Telescope_Science_Institute) (stsci.edu) |place=Baltimore, MD |url=http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/eras/huge-reflectors/page2.php }} {{cite book |last=Watson |first=Don Arthur |date=January 1986 |title=Construction Materials and Processes |publisher=McGraw-Hill |department=Gregg Division |isbn=9780070684768 |language=en |url=https://books.google.com/books?id=NKVRAAAAMAAJ |via=Google Books }} }} ==External links== *[https://web.archive.org/web/20110510201943/http://tions.net/CA256EA900408BD5/vwWWW/house~04~16 Tions.net], Diy mirror / mirroring / silvering Category:Chemical processes Category:Mirrors Category:Silver --- Adapted from the Wikipedia article [Silvering](https://en.wikipedia.org/wiki/Silvering) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Silvering?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.