Potassium alum mineral salt, the potassium double sulfate of aluminum, is a unique mineral because it has antiseptic and astringent properties that are particularly useful for wet shavers.  When rubbed on wet skin, alum provides a mild stinging sensation similar to that of an alcohol-based aftershave splash and it helps to close pores and tighten the skin while also sealing any small nicks from shaving.  Prior to the invention of antibiotics, alum blocks were used regularly to prevent infections that might have occurred from nicks or cuts. While alum blocks are typically cut into square or rectangular blocks, a more innovative alum product has been designed for the traditional wet shaver, the RazoRock.