aqueous iron rust
Technical term for rust formed in water or moisture, often seen in contexts like plumbing, metal corrosion, or traditional ironwork.
Aqueous iron rust came out of the old water pipe, turning the water red.
Compound of 鉄 (iron) and 渋 (astringent, rough). The exact historical derivation is uncertain; the term likely arose from the appearance or texture of wet iron rust.