Glass coloring and color marking may be obtained by 1) addition of
coloring ions, by 2) precipitation of nanometer sized colloides
(so-called striking glasses such as "gold ruby" or red "selenium
ruby"), 3) by colored inclusions (as in milk glass and smoked
glass), 4) by light scattering (as in phase separated glass), 5) by
dichroic coatings (see dichroic glass), or 6) by colored coatings.
1 Coloring ions
2 Striking glasses
3 Colored inclusions
Color caused by scattering
6 See also
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:
Uranium glass glowing under UV light
Cobalt glass for decoration
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.
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 is one of the oldest glass additives, and purple manganese
glass was used since early Egyptian history.
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.
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 with added nickel acquires purplish
Nickel together with a small amount of cobalt was used for
decolorizing of lead glass.
Chromium is a very powerful colorizing agent, yielding dark green
or in higher concentrations even black color. Together with tin oxide
and arsenic it yields emerald green glass.
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
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
Adding titanium produces yellowish-brown glass. Titanium, rarely used
on its own, is more often employed to intensify and brighten other
Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or
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 gives green color (used in UV filters) or lilac red.
Cranberry glass bowl
Photochromic eyeglass lens. The coloring is caused by silver
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, it yields a brilliant red color known as
Pure metallic copper produces a very dark red, opaque glass, which is
sometimes used as a substitute for gold in the production of
Metallic gold, in very small concentrations (around 0.001%, or 10
ppm), produces a rich ruby-colored glass ("
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 gold glass is usually made of lead
glass with added tin.
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.
Tin oxide with antimony and arsenic oxides produce an opaque white
glass (milk glass), first used in
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 caused by scattering
Tyndall effect in opalescent glass: it appears blue from the side,
but orange light shines through.
Porous glass pore-size gradient (large pores on the right); coloring
based on the Tyndall effect.
Glass containing two or more phases with different refractive indices
shows coloring based on the
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.
A pendant made from dichroic glass
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.
Crystal field theory
Crystal field theory - physical explanation coloring
Color of medieval stained glass
Hydroxyl ion absorption
^ 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,
^ a b c Werner Vogel: "
Glass Chemistry"; Springer-Verlag Berlin and
Heidelberg GmbH & Co. K; 2nd revised edition (November 1994),
^ Formation of
Gold Nanoparticles in
Ruby Glass: The influence of
^ 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
^ Chemical Fact Sheet -
Chromium www.speclab.com. Retrieved 3 August
^ a b R. Barbour. "Glassblowing for Laboratory Technicians" (PDF).
wiredfreak.com. Archived from the original (PDF) on 26 March 2012.
Retrieved 9 April 2014.
Glass www.glassassociation.org.uk (Barrie Skelcher).
Retrieved 3 August 2006
^ "Selenium". Illustrated
Glass Dictionary. www.glassonline.com.
Archived from the original on 1 October 2011. Retrieved 9 April
^ "Why is the sky blue, and sunsets red?:
Blue and Red". Causes of
Color. Institute for Dynamic Educational Advancement. Retrieved 23