Depot - After shave alum stone. The alum or potassium alum is a mixture of aluminum and potassium salt of sulfuric acid which at room temperature is presented as a colorless solid, odorless and totally natural. It is a perfect for use after shaving thanks to the astringent and hemostatic capabilities. This natural mineral is also used as a natural hypoallergenic. Usage Wet the skin with cold water and gently rub the alum stone onto the shaved area. Leave on for a few seconds and splash face with warm water. For best maintenance of the stone, pat dry after use.