Have you ever wondered about the chemistry of colored glass? Early glass got its color either from natural impurities in the sand used to make the glass or the smoke from the coal used to melt the sand. For example, the dark green to nearly black “black bottle glass” from 17th century England got its color from iron in the sand and sulfur in the coal. But, most glass gets its color from intentional additions of elements and compounds. Here is a look at colored glass chemistry.
Elements and Compounds That Color Glass
This table lists elements and compounds that color soda-lime glass. Keep in mind, the ingredients may also be mixed to create intermediate colors. Also, the transition metals display several oxidation states, so a single element may yield multiple colors, depending on conditions.
copper + tin
selenium + cadmium
|ruby glass, cranberry glass
gold + tin(II) chloride
Purple of Cassius
|cadmium sulfide (toxic)
lead with antimony
|Amber or Orange
cadmium + sulfur + selenium
|manganese + cobalt + iron
The Basics of Coloring Glass
Coloring glass isn’t always as easy as adding a certain amount of a particular element or compound to glass. Impurities in the glass may require a decolorizer to precipitate out iron and sulfur compounds so the glass starts out clear. Two common decolorizers are manganese dioxide and cerium oxide. Even then the chemical composition of the glass plays a large role in the colors produced by additives. Most glass is soda-lime glass, but other kinds of glass exist, such as borosilicate glass and leaded “crystal.” Ions from additives affect the glass differently. For example, sulfur compounds turn soda-lime glass shades of amber, but turn borosilicate glass blue.
In addition to adding colorant to glass, a surface coating may be applied. Varying the thickness of surface coatings can yield a rainbow of colors by light scattering. For example, iridescent glass results from applying thin layers of colloidal silver or gold. A clear glass coating over the layers protects the effect.
Also, color can change over time due to environmental factors. For example, old New England window glass that started out clear may be pale violet now due to chemical changes caused by sunlight. Surface-treated glass can change colors from oxidation in air or reaction with food or drink. Sometimes the effect is done intentionally. For example, spraying glass with tin chloride or lead chloride and heating the glass in a reducing atmosphere forms iris glass.
- De Jong, Bernard; et al. (2011) “Glass, 1. Fundamentals” in Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA. doi:10.1002/14356007.a12_365.pub3
- Nassau, Kurt (2001). The Physics and Chemistry of Color: The Fifteen Causes of Color. Wiley. ISBN 978-0-471-39106-7.
- Vogel, Werner (1994). Glass Chemistry (2nd revised ed.). Springer-Verlag . ISBN 3-540-57572-3.