Alkaline solutions are aqueous solutions of metal hydroxides. The best-known lyes are caustic soda, lye of potassium, lye of chlorine and lye of calcium. | The latter are mainly used in industry. Lyes dissolve fats and are therefore used as cleaning agents. In addition, they have a caustic effect, but do not attack metals (apart from zinc and aluminium). They are used in soap production, paper production, as a cleaning agent or as a paint remover.