Glass coloring and color marking

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.

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:

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).

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.

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