How does the color of glass form?

How does the color of glass form?

In the family of various glass, besides the transparent glass that we often see in daily life, it still has a few kinds of colorful glass. So how do these gorgeous colorful glasses come into being?

Generally glass is made by smelting quartz sand, soda ash and limestone together.  It is a silicate mixture with variable composition. At initial, the glass people made was small pieces of glass with poor transparency and some color. Its color is not consciously added, because the raw material used is not pure, mixed with the impurities. At that time, the colored glass was only used for decoration, and the requirements were not high. But today's colored glass has a high technology, which can only be made after the secret of the color of the glass is revealed.

After study, people discover if we add 0.4% ~ 0.7% colouring agent into the ingredient of common glass, we can make glass has color. Colouring agent is mostly the oxide of metal. Each metallic element has its own unique "spectral characteristics", so different metal oxides can take on different colors. If these oxides are added to the glass mix, the glass is colored. For example, adding chromium oxide the glass turns green. Adding manganese dioxide, the glass appears purple. Adding cobalt oxide, the blue color of the glass is used to make protective glasses for steelworkers and welders.