The 5% caustic potash solution (potassium hydroxide, KOH) is an alkaline solution used in various areas of the laboratory and industry. In microbiology, it is used to distinguish yeasts and filamentous fungi by soaking samples in the solution and then examining them microscopically.

In the chemical industry, potassium hydroxide is used in the manufacture of soaps and detergents, while it is also used in the textile and food industries. In the laboratory, it can be used as an etchant to remove proteins and grease from glassware or to neutralize acids.
In industry, KOH is mainly used for anisotropic etching of silicon and as an electrolyte. In addition, potassium hydroxide is used as an etching additive in metallography to make certain structures in metals visible.