Leather is a natural product which means that there are chances it will burn during engraving or cutting with the laser; it also produces a particular smell. Furthermore, the cutting edges can turn dark and stain. Many different types of leather can be cleans but it is important to test the cleaning method at a discreet place. First off, try to remove the smoke residue with a dry cloth. If that does not work, try cleaning the leather with a damp cloth or an alcohol-based cleaner.