Alum-tawed (aka alum-tan) leather is not safe for laser cutting based on the following information:
Aluminum Sulfate itself does not burn. POISONOUS GASES ARE PRODUCED IN FIRE, including Aluminum Oxides and Sulfur Oxides.
https://www.nj.gov › health › eoh › rtkweb › documents
Alum tawing is an ancient process of treating prepared animal hides with aluminum salts and other materials. The skins are then left to dry for several weeks to allow the development of stabilization effects. Alum Tawed skins are typically sort and flexible to the touch, and have a high degree of stretch.
Aluminum Sulfate Anhydrous is an aluminum salt