Alum stone is a common name for a type of natural deodorant and aftershave that is popular in France under the name Pierre d’alun and found throughout Europe. In the U.S. alum stone is typically known as crystal deodorant. The cosmetic and personal care use of alum stone dates back to antiquity due to is simple, yet powerful cosmetic formula. Alum stone is made of potassium alum and comes from the Greek word Alos. It was originally used as an aftershave, but since the 1980s alum stone has been marketed as a deodorant. Now many deodorant and aftershave brands utilize the term alum stone and crystal deodorant to describe and classify their product. But it is important to note that alum stone is the type or name of the product, not the ingredient.
The active ingredient of alum stone, potassium alum, is a naturally occurring mineral salt. The cosmetic effectiveness of natural potassium alum has led to the commercialization of the mineral salt. In order for manufacturers to commercially apply potassium alum large quantities must be extracted from deposits in the Earth’s crust. This process is expensive and long. Due to modern technological advancements manufacturers can now create synthetic potassium alum by mixing aluminum hydroxide with potassium or ammonium sulfate in sulfuric acid. Therefore, there exist two types of potassium alum stone deodorants and aftershaves, natural and synthetic.
Natural alum stone is a translucent crystalline colorless stone commercially called ”Kalunite” and occurs in an octahedral crystal form. It is a common mistake to confuse kalunite with “alunite”, due to the similiarities of name. Kalunite and alunite are two different minerals. Alunite is a pinkish to grey colored opaque stone, whereas “kalunite” with a ‘K’ is a translucent colorless crystal, which mineral name is AlumK or Potassium alum. The images to the right clearly show the difference between the two types of minerals.