Re: How is colored glass made?

Ian,

Colored glass is made by adding colored minerals to the melted glass or by 
actually painting the glass with special paints.  The best way to see this 
is to visit a local artist who works with stained glass.

I am adding a more complete discussion with some web sites that discuss 
colored glass.
Some sites on colored glass
 http://www.ndga.net/
 http://www.ccgallery.com/Vision
s.htm
 http://www.p
hotonics.com/Directory/lphtml/bgf/26850.htm
 http://www.stainedglass.org/main_pages/association_pages/historySG.html



Searches on colored glass, stained glass, photochromic glass on MSN search 
and Altavista give thousands of sites, but it is hard to find specific 
information on the composition and fabrication of these glasses.  Do a few 
searches; find some sites that interest you and make some phone calls to 
companies and artists who manufacture glass and work with glass.  I am 
getting the impression that this topic can become a lifelong avocation or 
vocation.

Colorless glasses are mixtures of oxides of the alkali and alkaline earth 
metals with silica, alumina, boric oxide, and other "colorless " metal 
oxides and salts.  Certain heavy metal oxides are added to increase the 
refractive index and make the glass sparkle.  Unless the glasses are 
specially formulated they usually absorb light in the near uv and the near 
ir .  Addition of the oxides of the transition metals and of the 
lanthanides and actinides, these oxides are usually colored, and sometimes 
even the actual metals impart colors thruout the glass.  These colors can 
be a subtle yellow from trace iron to the dark intense cobalt blue.  
Chromium, manganese, cobalt, copper, silver, gold impart various colors to 
glass and to natural and artificial gemstones  http://www.geology.wisc.e
du/~jill/306.html   http://www.geology.wisc
.edu/~jill/Lect7.html   This site gives an 
excellent discussion on color in gems with splendid pictures.

Addition of clays and other insoluble materials will cause glass to become 
cloudy or opalescent and can cause optical effects such as scattering and 
diffraction.  The best example of this is the star sapphire.  The star is 
a diffractive effect caused by dispersion of rutile [TiO2] crystals in the 
corundum[Al2O3] matrix. 

Stained glass is made by a variety of techniques that involve painting, 
diffusing materials into clear glass and by introducing colorants into the 
melt.  One technique that I observed by a master glass craftsman who was a 
refugee from Holland during WWII and worked for Lamb Studios was that he 
cut pieces of clear glass to match his pattern.  Then he painted the glass 
with special pigments blending the colors on the glass.  When this phase 
was done the glass pieces were dark and dull with really no visual color.  
He the annealed the glass and the paint either fused or diffused into the 
glass and the resultant glass was brilliantly colored with fine tones and 
detail.  He never told me what the paints were.

Another way of coloring glass is to vacuum deposit thin layers of various 
materials or metals. These can act as filters or interference filters and 
color by selectively reflecting some wavelengths and either absorbing or 
transmitting others.  In any case it is worth while considering that any 
color effect is usually a mixture of reflection, transmission and 
absorption combined with the effects of scattering, diffraction and 
refraction.  Certain colored materials are one color by reflected and 
[usually] the complementary color by transmitted light.  Many colored 
materials also emit color by fluorescence or phosphorescence and sometimes 
even by laser emission.

Photochromism its simplest form, such as Photogray sunglasses, is usually 
caused by the action of uv or blue light causing a photochemical 
reaction.  In this case added silver chloride is excited to a charge 
transfer complex [or possibly matrix immobilized silver and chlorine 
atoms] that absorb visible light.  When the uv and blue light is 
diminished the silver and chlorine atoms revert to silver chloride which 
doesn’t appreciably absorb visible light and the lenses get lighter. 

I hope I have at least given you some ideas about the subject.  Check out 
some of the web sites and contact some people from your locality working 
in the field you are interested in.