It is found that if 0.4 ~ 0.7% colorant is added to the composition of ordinary glass, the glass can be colored. Colorants are mainly metal oxides. We already know 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 batch, the glass will be colored. For example, when chromium oxide (Cr2O3) is added, the glass turns green; Manganese dioxide (MnO2 _ 2) was added to make the glass purple. When cobalt oxide (Co2O3) is added, the glass is blue, which is the protective eyepiece used by steel workers and welders.
In fact, the color of glass depends not only on the added colorant, but also on the melting temperature and the properties of furnace flame to adjust the valence of elements, so that the glass presents different colors. For example, copper in glass, if high-priced copper oxide exists, the glass appears blue-green; In the presence of cuprous oxide (Cu2O), glass is red. Sometimes, the first melting can't make the glass show well, and it needs secondary heating to make the glass show color. This is the case with precious golden red glass, which is made by adding a small amount of gold to ordinary glass components and firing. After the first melting, gold is distributed in the glass in the form of atoms, and the glass does not develop color at this time; When heated to a temperature close to softening again, the gold atoms in it polymerize into colloidal particles, and then the glass appears beautiful red.
Nowadays, people use oxides of rare earth elements as colorants to make various high-grade colored glasses. Colored glass doped with rare earth elements has clear tone and bright color, and even changes color under different light. For example, neodymium oxide glass has this characteristic. It's purple in the sun and blue-purple in the fluorescent light, which is very beautiful. There is a kind of glass that changes color with the intensity of light. People use it as lenses for glasses and window glass for houses. Using this kind of glass as window glass can keep a certain brightness indoors, and it is no longer necessary to use curtains to shade the sun, so some people call it "automatic curtains". It can also block the passage of ultraviolet rays in the sun. After installing this glass in libraries and museums, books and cultural relics can be protected from ultraviolet rays.
In addition to rare earth elements, tungsten and platinum can be directly added to the glass, and it can also be made into color-changing glass.
Ordinary pigments fade due to the irradiation of ultraviolet rays from the sun or the action of oxygen and sulfur dioxide in the air; However, stained glass can withstand the sun and rain and keep a beautiful youthful appearance forever, because oxides such as metals that play a coloring role have been integrated with glass. With the development of science and technology, the varieties of stained glass will become more and more colorful, and our life will become colorful because of its embellishment and decoration.