Adding substances that can form colouring ions, compound colloids and metal colloidal particles to glass raw materials to make them present different colours can be divided into four types according to the colouring mechanism: (1) Ion colouring: Compounds containing transition elements such as cobalt (Co), manganese (Mn), nickel (Ni), iron (Fe), copper (Cu) and so on are added to the glass. They exist in the ionic state in the glass. Because their valence electrons transit between different levels (ground and excited states), selective absorption of visible light is induced and coloured, such as cobalt blue, manganese violet and nickel. Green and other color glass. (2) Colloidal particle colouring of compounds: Compounds containing sulphur or selenium (such as CdS, CdSe, etc.) are added to the glass containing zinc (ZnO), CdO, ZnS, ZnSe are formed in the glass, and then heat-treated twice below annealing temperature to form CdS, CdSe and grow into larger colloidal particles, which are coloured by light scattering, such as selenium red. Color glass such as cadmium yellow. (3) Colloidal particle colouring: adding oxides (such as gold, silver and copper) which are easy to decompose into metal state to glass raw materials, dissolving in ionic state first, transforming into atom state after heat treatment, aggregating and growing into colloidal particles, and colouring due to absorption of visible light caused by light scattering, such as gold red and copper. Red, silver and yellow color glass, etc. (4) Semiconductor colouring: adding CdS, CdSe, CdTe and other colouring agents to glass, there is no absorption peak in the visible region but a continuous absorption zone. The transmission zone and absorption zone are a very steep boundary. Different from the above-mentioned colouring mechanisms, their colours change with the ratio of CdS/CdSe. For example, CdS often approaches orange. CdSe tends to be red, while CdTe tends to be black, i.e. they move towards long wave in the order of O 2-, S 2-, Se 2-, Te 2-. According to the band theory of semiconductors, the electrophilic potential of these anions decreases in turn, and the valence electrons of these anions can be excited to the conduction band (excited state) with lower energy (near visible light) in turn, so that their truncated wave limit enters the visible region, leading to glass coloration. Allen@antiquemirror.cn