How is the colored glass made?

Ordinary glass is melted with quartz sand, soda ash and limestone. It is a mixture of silicates with an indefinite composition. The first glass made by people is some small pieces of glass with poor transparency and some colors. Its color is not consciously added by people, but the result of impure raw materials mixed with impurities. At that time, the colored glass was only used as decorations, and the requirements were not high. People only produced colored glass by chance. However, the color glass we require today has high scientific requirements, which can be manufactured only after the secret of glass color is revealed.

After research, it is found that if 0.4 ~ 0.7% colorant is added to the ingredients of ordinary glass, the glass can be colored. Colorants are mostly metal oxides. We have already known that each metal element has its unique "spectral characteristics", so different metal oxides can show different colors. If these oxides are added to the glass ingredients, the glass will be colored. Cr2O3 (green oxide glass), for example; When manganese dioxide (MnO2) is added, the glass is purple; Cobalt oxide (Co2O3) is added, and the glass is blue. The protective eyepiece for steelworkers and welders is made of this kind of glass.
In fact, in addition to the added colorants, people also adjust the valence of elements through the melting temperature and the nature of furnace flame, so that the glass presents different colors. For example, if copper in glass exists in high priced copper oxide, the glass appears blue-green; In the presence of low-cost cuprous oxide (Cu2O), the glass is red. Sometimes, the glass can't show well after one time of melting, and it needs a second heating to show the color of the glass. This is the case with precious golden red glass. It is made by adding a small amount of gold to ordinary glass ingredients. After the first melting, gold is distributed in the glass in the form of atoms, and the glass does not show color at this time; When heated to a temperature close to softening again, the gold atoms polymerize into colloidal particles, and the glass shows a beautiful red.
Now, people use the oxides of rare earth elements as colorants to make all kinds of high-grade color glasses. The color glass mixed with rare earth elements has bright and clean colors and even changes colors in different light. For example, neodymium oxide glass has this characteristic. It shows purplish red under sunlight and blue purple under fluorescence. It is very beautiful.
In addition to rare earth elements, color changing glass can also be made by directly adding tungsten and platinum to the glass.

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