Glass comes in a variety of colors, from clear glass windows to amber beer bottles. Colored glass is important because it protects its contents from the damaging effects of light. The harmful types of light are primarily light with wavelengths from 290 to 450nm. Blocking these specific wavelengths prevents the contents of a container from degrading. This is particularly important with volatile pharmaceutical compounds. Containers that hold drugs for oral use must not exceed 10% transmission.
Glass is colored by adding specific materials, such as mineral salts, to the ingredients. Three common colors of glass are amber (brown), green and blue. Amber glass is produced by adding sulfur to the ingredients. Green glass may contain iron oxide and/or chromium, and/or didymium. Blue glass is made by adding materials such as cobalt oxide.
The benefits of colored glass vary by what color is used. Amber glass, for example blocks UV light most efficiently, and is therefore used for beer bottles. Green glass offers moderate protection from light, and therefore is used while bottling wine and juice, which can handle some light exposure. Chemistry flame tests sometimes use blue glass to more clearly see some elements.