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Glass
Glass
coloring and color marking may be obtained by 1) addition of coloring ions,[1][2] by 2) precipitation of nanometer sized colloides (so-called striking glasses[1] such as "gold ruby"[3] or red "selenium ruby"),[2] 3) by colored inclusions (as in milk glass and smoked glass), 4) by light scattering (as in phase separated glass),[2] 5) by dichroic coatings (see dichroic glass), or 6) by colored coatings.

Contents

1 Coloring ions 2 Striking glasses 3 Colored inclusions 4 Color
Color
caused by scattering 5 Dichroic
Dichroic
glass 6 See also 7 References

Coloring ions[edit]

Iron(II) oxide
Iron(II) oxide
glass

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:

Amber Glass

Uranium glass
Uranium glass
glowing under UV light

Cobalt glass
Cobalt glass
for decoration

Iron(II) oxide
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. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black. In borosilicate glasses rich in boron, sulfur imparts a blue color. With calcium it yields a deep yellow color.[4] Manganese
Manganese
can be added in small amounts to remove the green tint given by iron, or in higher concentrations to give glass an amethyst color. Manganese
Manganese
is one of the oldest glass additives, and purple manganese glass was used since early Egyptian history. Manganese
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
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.[5] Small concentrations of cobalt (0.025 to 0.1%) yield blue glass. The best results are achieved when using glass containing potash. Very small amounts can be used for decolorizing. 2 to 3% of copper oxide produces a turquoise color. Nickel, depending on the concentration, produces blue, or violet, or even black glass. Lead crystal
Lead crystal
with added nickel acquires purplish color. Nickel
Nickel
together with a small amount of cobalt was used for decolorizing of lead glass. Chromium
Chromium
is a very powerful colorizing agent, yielding dark green[6] or in higher concentrations even black color. Together with tin oxide and arsenic it yields emerald green glass. Chromium
Chromium
aventurine, in which aventurescence was achieved by growth of large parallel chromium(III) oxide plates during cooling, was also made from glass with added chromium oxide in amount above its solubility limit in glass. Cadmium
Cadmium
together with sulphur forms cadmium sulfide and results in deep yellow color, often used in glazes. However, cadmium is toxic. Together with selenium and sulphur it yields shades of bright red and orange.[7] Adding titanium produces yellowish-brown glass. Titanium, rarely used on its own, is more often employed to intensify and brighten other colorizing additives. Uranium
Uranium
(0.1 to 2%) can be added to give glass a fluorescent yellow or green color.[8] Uranium glass
Uranium glass
is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. When used with lead glass with very high proportion of lead, produces a deep red color. Didymium
Didymium
gives green color (used in UV filters) or lilac red.[7]

Striking glasses[edit]

Cranberry glass
Cranberry glass
bowl

Photochromic eyeglass lens. The coloring is caused by silver nanoparticles.

Selenium, like manganese, can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish color, caused by selenium nanoparticles dispersed in glass. It is a very important agent to make pink and red glass. When used together with cadmium sulfide,[9] it yields a brilliant red color known as " Selenium
Selenium
Ruby". Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-colored glass. Metallic gold, in very small concentrations (around 0.001%, or 10 ppm), produces a rich ruby-colored glass (" Ruby
Ruby
Gold" or "Rubino Oro"), while lower concentrations produces a less intense red, often marketed as "cranberry". The color is caused by the size and dispersion of gold particles. Ruby
Ruby
gold glass is usually made of lead glass with added tin. Silver
Silver
compounds such as silver nitrate and silver halides can produce a range of colors from orange-red to yellow. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. Also photochromic lenses and photosensitive glass are based on silver.

Colored inclusions[edit] Tin
Tin
oxide with antimony and arsenic oxides produce an opaque white glass (milk glass), first used in Venice
Venice
to produce an imitation porcelain. Similarly, some smoked glasses may be based on dark-colored inclusions, but with ionic coloring it is also possible to produce dark colors (see above). Color
Color
caused by scattering[edit]

The Tyndall effect
Tyndall effect
in opalescent glass: it appears blue from the side, but orange light shines through.[10]

Porous glass
Porous glass
pore-size gradient (large pores on the right); coloring based on the Tyndall effect.

Glass
Glass
containing two or more phases with different refractive indices shows coloring based on the Tyndall effect
Tyndall effect
and explained by the Mie theory, if the dimensions of the phases are similar or larger than the wavelength of visible light. The scattered light is blue and violet as seen in the image, while the transmitted light is yellow and red. Dichroic
Dichroic
glass[edit] Main article: Dichroic
Dichroic
glass

A pendant made from dichroic glass

Dichroic
Dichroic
glass has one or several coatings in the nanometer-range (for example metals, metal oxides, or nitrides) which give the glass dichroic optical properties. Also the blue appearance of some automobile windshields is caused by dichroism. See also[edit]

Crystal field theory
Crystal field theory
- physical explanation coloring Color
Color
of medieval stained glass Hydrogen darkening Hydroxyl ion absorption Transparent materials

References[edit]

^ a b Bernard H. W. S. De Jong, Ruud G. C. Beerkens, Peter A. van Nijnatten: "Glass", in: "Ullmann's Encyclopedia of Industrial Chemistry"; Wiley-VCH Verlag GmbH & Co. KGaA, 2002, doi:10.1002/14356007.a12_365 ^ a b c Werner Vogel: " Glass
Glass
Chemistry"; Springer-Verlag Berlin and Heidelberg GmbH & Co. K; 2nd revised edition (November 1994), ISBN 3-540-57572-3 ^ Formation of Gold
Gold
Nanoparticles in Gold
Gold
Ruby
Ruby
Glass: The influence of Tin ^ Substances Used in the Making of Coloured Glass 1st-glass.1st-things.com (David M Issitt). Retrieved 9 April 2014 ^ Nassau, Kurt (2001). The physics and chemistry of color: the fifteen causes of color. Wiley. ISBN 978-0-471-39106-7. Retrieved 4 April 2013.  ^ Chemical Fact Sheet - Chromium
Chromium
www.speclab.com. Retrieved 3 August 2006 ^ a b R. Barbour. "Glassblowing for Laboratory Technicians" (PDF). wiredfreak.com. Archived from the original (PDF) on 26 March 2012. Retrieved 9 April 2014.  ^ Uranium
Uranium
Glass
Glass
www.glassassociation.org.uk (Barrie Skelcher). Retrieved 3 August 2006 ^ "Selenium". Illustrated Glass
Glass
Dictionary. www.glassonline.com. Archived from the original on 1 October 2011. Retrieved 9 April 2014.  ^ "Why is the sky blue, and sunsets red?: Blue
Blue
and Red". Causes of Color. Institute for Dynamic Educational Advancement. Retrieved 23 April

.