酸洗是一种金属表面处理方法，用于除去污渍、锈等。

酸洗主要使用盐酸或硫酸。盐酸虽然比硫酸贵，但它速度快，同时金属损耗小。碳素钢通常用盐酸或硫酸酸洗。合金钢常用磷酸，硝酸或氢氟酸。耐酸性强的铬镍钢需要用盐酸和硝酸酸洗。大多数铜合金用稀硫酸，但黄铜用浓硫酸、硝酸与氯化钠和煤烟的混合液酸洗。钢板酸洗后，若暴露于高湿度的环境下，会氧化生锈。因此，要涂一层油膜或防水涂料。此油膜必须在电镀或涂漆前去除。

A mordant is a substance used to set dyes on fabrics or tissue sections by forming a coordination complex with the dye which then attaches to the fabric or tissue. It may be used for dyeing fabrics, or for intensifying stains in cell or tissue preparations. The term mordant comes from the present participle of French mordre, "to bite". In the past, it was thought that a mordant helped the dye bite onto the fiber so that it would hold fast during washing. A mordant is often a polyvalent metal ion. The resulting coordination complex of dye and ion is colloidal and can be either acidic or alkaline.