@RHensley looked it up and it also says about hyalin this...
Produced since 1878, Féret parfumeur’s Bloc Hyalin is renowned for its purifying properties: a natural, invisible deodorant that inhibits the growth of odor-causing bacteria, it also acts as an astringent, ideal for use before or after shaving. Inside the distinctive petite boite jaune (little yellow box) is a matchbox-sized slab of potassium alum, a naturally occurring form of aluminum salt harvested from mineral deposits in Panama, melted down to remove impurities, and reconstituted in the form of a block that will provide a year of soothing and freshening power.