iron mordant

例句：

1. 1. The old iron door is coveredin a layer of rust.
   那扇旧铁门上覆盖着一层锈。
2. 2. The painton the iron fence has turned to rust.
   铁栅栏上的油漆已经变成了锈。
3. 3. The ironmordant was used to protect themetal from corrosion.
   铁锈被用来保护金属免受腐蚀。