Glass coloring and color marking


Glass coloring and color marking may be obtained by in several ways.
  1. by the addition of coloring ions,
  2. by precipitation of nanometer sized colloides,
, 1st century, Begram Hoard
  1. by colored inclusions
  2. by light scattering
  3. by dichroic coatings, or
  4. by colored coatings

    Coloring ions

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:
glowing under UV light
for decoration
The principal methods of this are enamelled glass, essentially a technique for painting patterns or images, used for both glass vessels and on stained glass, and glass paint, typically in black, and silver stain, giving yellows to oranges on stained glass. All of these are fired in a kiln or furnace to fix them, and can be extremely durable when properly applied. This is not true of "cold-painted" glass, using oil paint or other mixtures, which rarely last more than a few centuries.

Colored inclusions

with antimony and arsenic oxides produce an opaque white glass, first used in Venice to produce an imitation porcelain, very often then painted with enamels. Similarly, some smoked glasses may be based on dark-colored inclusions, but with ionic coloring it is also possible to produce dark colors.

Color caused by scattering

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.

Dichroic glass

Dichroic glass has one or several coatings in the nanometer-range which give the glass dichroic optical properties. Also the blue appearance of some automobile windshields is caused by dichroism.