question: Why does a tunnel of mirrored mirrors turn "green"?
comment: It turns green because mirrors are not completely clear, they have a small green tint that gets added if you do the infinite mirror thing
passages: Section::::Colours.:Green glass.
  
  While very pale green is the typical colour of transparent glass, deeper greens can be achieved by the addition of Iron(II) oxide which results in a bluish-green glass. Together with chromium it gives glass of a richer green colour, typical of the glass used to make wine bottles.
  
  The addition of chromium yields dark green glass, suitable for flashed glass. Together with tin oxide and arsenic it yields emerald green glass.
  
  Section::::Colours.:Blue glass.
   BULLET::::- Reflected Color - Uncoated glass reflects light uniformly and does not cause reflected light to be distorted (a white light source reflected in a non-coated glass pane will still appear white). However, anti-reflective coatings typically cause some wavelengths of light to be reflected more than others, causing a "shift" in the reflected color. This way, a white light source reflected in an anti-reflected glass surface may appear green or blue or red, depending on the wavelengths that are favored by a particular anti-reflective coating design.
   BULLET::::- Intensity of Reflected Color - intensity of reflected color can be measured by its relative distance from the color neutral zone (i.e. white). Due to the variability of industrial processes, some producers design their anti-reflective coatings to have more intense colors so that the statistical deviation of outcomes falls within a specific color (green or blue, etc.). The tighter a manufacturer's control of its processes, the closer the design can be to the color neutral zone, without crossing over from a designated color.
   As the color change is persistent and energy need only be applied to affect a change, electrochromic materials are used to control the amount of light and heat allowed to pass through windows ("smart windows"), One popular application is in the automobile industry where it is used to automatically tint rear-view mirrors in various lighting conditions.
  
  Section::::Electrochromic materials.
  
  Among the metal oxides, tungsten oxide (WO), has been the most extensively studied material.
   Carnival glass gets its iridescent sheen from the application of metallic salts while the glass is still hot from the pressing. A final firing of the glass brings out the iridescent properties of the salts, giving carnival glass the distinct shine it is known for.
  
  Section::::History.
   BULLET::::- Manganese dioxide, which is black, is used to remove the green color from the glass; in a very slow process this is converted to sodium permanganate, a dark purple compound. In New England some houses built more than 300 years ago have window glass which is lightly tinted violet because of this chemical change; and such glass panes are prized as antiques. This process is widely confused with the formation of "desert amethyst glass", in which glass exposed to desert sunshine with a high ultraviolet component develops a delicate violet tint. Details of the process and the composition of the glass vary and so do the results, because it is not a simple matter to obtain or produce properly controlled specimens.
   For the explorers to have seen a green rim on and off for 35 minutes there must have been some mirage effect present.
   This color is also called "regular green". It is at precisely 120 degrees on the HSV color wheel, also known as the RGB color wheel (). Its complementary color is magenta.
  
  Another name for this color is "green" as opposed to the darker "HTML/CSS green" and the deeper "pigment green", both shown below.
  
  Green takes up a large portion of the CIE chromaticity diagram because it is in the central area of human color perception.
  
  Section::::Computer web color greens.:Green (HTML/CSS color).
   Section::::Microelectromechanical Mirrors (MEMS).
   In additive color devices such as computer displays and televisions, one of the primary light sources is typically a narrow-spectrum yellowish-green of dominant wavelength ~550nm; this "green" primary is combined with an orangish-red "red" primary and a purplish-blue "blue" primary to produce any color in betweenthe RGB color model. A unique green (green appearing neither yellowish nor bluish) is produced on such a device by mixing light from the green primary with some light from the blue primary.
  
  Section::::In science.:Lasers.
   Living cells have been used to produce laser light. The cells were genetically engineered to produce green fluorescent protein (GFP). The GFP is used as the laser's "gain medium", where light amplification takes place. The cells were then placed between two tiny mirrors, just 20 millionths of a meter across, which acted as the "laser cavity" in which light could bounce many times through the cell. Upon bathing the cell with blue light, it could be seen to emit directed and intense green laser light.
  
  Section::::Uses.
   Section::::Applications.
  
  Section::::Applications.:Reductive dehalogenation.
   First generation electrochromic technologies tend to have a yellow cast in their clear states and blue hues in their tinted states. Darkening occurs from the edges, moving inward, and is a slow process, ranging from many seconds to several minutes (20-30 minutes) depending on window size. Newer electrochromic technologies eliminate the yellow cast in the clear state and tinting to more neutral shades of gray, tinting evenly rather than from the outside in, and accelerate the tinting speeds to less than three minutes, regardless of the size of the glass. Electrochromic glass provides visibility even in the darkened state and thus preserves visible contact with the outside environment. 
   Chirped mirrors are also found in structurally colored biological systems, including the shiny golden and silver color of certain beetles' elytra, e.g. Ruteline genus "Chrysina". In these cases, the chirped mirror generates complex color (such as gold or silver) when illuminated by white light by simultaneously reflecting a broad range of monochromatic colors.
  
  Section::::Simple explanation.
   Ordinary soda-lime glass appears colourless to the naked eye when it is thin, although iron oxide impurities produce a green tint which becomes evident in thick pieces or can be seen with the aid of scientific instruments. A number of additives are used to reduce the green tint, particularly if the glass is to be used for plain window glass, rather than stained glass windows. Additives that reduce the green tint include manganese dioxide which produces sodium permanganate, and may result in a slightly mauve tint, characteristic of the glass in older houses in New England. Selenium has been used for the same purpose.
   An announcement in 2009 of a direct green laser (which does not require doubling) promises much higher efficiencies and could foster the development of new color video projectors.
  
  In 2012, Nichia and OSRAM developed and manufactured merchant high-power green laser diodes (515/520 nm), which can emit green laser directly.
   Section::::Background.
   Section::::Technology.
  
  Section::::Technology.:Optical filters.
   By controlling the thickness and density of metal coatings, it is possible to decrease the reflectivity and increase the transmission of the surface, resulting in a "half-silvered mirror". These are sometimes used as "one-way mirrors".
   BULLET::::- Brise soleil is a natural lighting option that uses permanent architectural sun-shading techniques to reduce the amount of light that enters a building or a museum.
   The model is based on the idea that the perceptual colour scission following transparency
  
  is the opposite of colour fusion in a rotating episcotister, i.e. a rotating disk that alternates
  
  open and solid sectors.
  
  Metelli referred to colour fusion in a physical situation in which an episcotister rotates in
  
  front of an opaque background of reflectance A; the episcotister has an open sector of size t (a
  
  proportion of the total disk) and a solid sector of size (1-t) having reflectance r. The
  
  reflectance of the solid sectors and that of background are fused by rotation to produce a
   The effect is most commonly demonstrated with a device known as Benham's top. It can also be seen in stroboscopic lights when flashes are set at certain critical speeds. Rotating fan blades, particularly aluminum ones, can also demonstrate the effect; as the fan accelerates or decelerates, the colors appear, drift, change and disappear. The stable running speed of the fan does not (normally) produce colors, suggesting that it is not an interference effect with the frequency of the illumination flicker.
   SPDs can be manually or automatically "tuned" to precisely control the amount of light, glare and heat passing through.
  
  Section::::Electrically switchable smart glass.:Electrochromic devices.
  
  Electrochromic devices change light transmission properties in response to voltage and thus allow control over the amount of light and heat passing through. In electrochromic windows, the electrochromic material changes its opacity. A burst of electricity is required for changing its opacity, but once the change has been effected, no electricity is needed for maintaining the particular shade which has been reached. 
   Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron oxide impurities produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further metals and metal oxides can be added to glass during its manufacture to change its color which can enhance its aesthetic appeal. Examples of these additives are listed below:
  
  BULLET::::- Iron(II) oxide may be added to glass resulting in bluish-green glass which is frequently used in beer bottles. Together with chromium it gives a richer green color, used for wine bottles.
   Dichroic glass is specifically designed to be hotworked but can also be used in its raw form. Sculpted glass elements that have been shaped by extreme heat and then fused together may also be coated with dichroic afterwards to make them reflect an array of colors.
  
  Section::::Uses.:Architecture.
  
  The corporate headquarters of Amazon.com in Seattle, Washington incorporates dichroic glass into the exterior of its high-rise building, reflecting light into various colors that depend on the time of the day.
  
  Section::::External links.
  
  BULLET::::- Thesis – University of Neufchatel (Switzerland), PDF in English and French
  