天然染料媒染技术
Natural Dye Mordanting Technology
The earliest systematic use of metal-salt mordants to permanently fix natural dyes onto textile fibers — a coordination chemistry technique that not only prevents dye wash-out but also shifts the dye color, multiplying the palette from a single dyestuff.
Scientific Principle
Coordination chemistry of mordanting: Metal ions (Al³⁺ from alum/明矾, Fe²⁺/Fe³⁺ from iron-rich mud, Cu²⁺ from copper salts) form octahedral coordination complexes that act as bridges between dye molecules and fiber polymers. The dye's -OH and -C=O groups coordinate to the metal center, while the metal simultaneously coordinates to -OH groups on cellulose or -NH₂ groups on silk/wool protein fibers. This ternary complex (fiber-metal-dye) is insoluble and chemically stable, preventing wash-out. Different metals with the same dye produce different colors because the metal's d-orbital energy levels shift the dye's visible absorption spectrum via ligand field effects. Alum (KAl(SO₄)₂·12H₂O) was the most common ancient Chinese mordant due to its availability and the bright, clear tones it produces.