Commonly known as potash alum, potassium alum is the potassium double sulfate of aluminum. Potassium alum forms large octahedral crystals that are an opaque white in color. In the chemical industry, potassium alum is used in tanning leather, clarifying turbid liquids to precipitate contaminants, as a mordant for dyes, and as a means of making textile products fire resistant. In medicine, potassium alum is used to treat skin after shaving, as an astringent/styptic and antiseptic, reducing bleeding in minor cuts and nosebleeds, and to remove pimples and acne. Certain food ingredients such as baking powder include potassium alum as a means of providing a second leavening phase at higher temperatures. In use since the age of antiquity all over the world, potassium alum has long been a key ingredient in natural medical practices in both India and China, where it is still used today to treat bleeding and inhibit the growth of bacteria in wounds.